* [PATCH v3 0/5] mm: further simplify VMA merge operation
@ 2025-01-31 12:31 Lorenzo Stoakes
2025-01-31 12:31 ` [PATCH v3 1/5] mm: simplify vma merge structure and expand comments Lorenzo Stoakes
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: Lorenzo Stoakes @ 2025-01-31 12:31 UTC (permalink / raw)
To: Andrew Morton
Cc: Liam R . Howlett, Vlastimil Babka, Jann Horn, linux-mm, linux-kernel
While significant efforts have been made to improve the VMA merge
operation, there remains remnants of the bad (or rather confusing) old
days, which make the code difficult to understand, more bug prone and
thus harder to modify.
This series attempts to significantly improve matters in a number of
respects - with a focus on simplifying the commit_merge() function which
actually actions the merge operation - and importantly, adjusting the two
most confusing merge cases - those in which we 'adjust' the VMA immediately
adjacent to the one being merged.
One source of confusion are the VMAs being threaded through the operation
themselves - vmg->prev, vmg->vma and vmg->next.
At the start of the operation, vmg->vma is either NULL if a new VMA is
propose to be added, or if not then a pointer to an existing VMA being
modified, and prev/next are (perhaps not present) VMAs sat immediately
before and after the range specified in vmg->start, end, respectively.
However, during the VMA merge operation, we change vmg->start, end and
pgoff to span the newly merged range and vmg->vma to either be:
a. The ultimately returned VMA (in most cases) or
b. A VMA which we will manipulate, but ultimately instead return vmg->next.
Case b. especially here is confusing for somebody reading this code, but
the fact we update this state, along with vmg->start, end, pgoff only makes
matters worse.
We simplify things by replacing vmg->vma with vmg->middle and never
changing it - this is always either NULL (for a new VMA) or the VMA being
modified between vmg->prev and vmg->next.
We further simplify by placing the merged VMA in a new vmg->target field -
whether case b. above is the case or not. The reader of the code can now
simply rely on vmg->middle being the middle VMA and vmg->target being the
ultimately merged VMA.
We additionally tackle the confusing cases where we 'adjust' VMAs other
than the one we ultimately return as the merged VMA (this includes case
b. above). These are:
(1)
merge
<----------->
|------||--------| |------------|---|
| prev || middle | -> | target | m |
|------||--------| |------------|---|
In which case middle must be adjusted so middle->vm_start is increased as
well as performing the merge.
(2) (equivalent to case b. above)
<------------->
|---------||------| |---|-------------|
| middle || next | -> | m | target |
|---------||------| |---|-------------|
In which case next must be adjusted so next->vm_start is decreased as well
as performing the merge.
This cases have previously been performed by calculating and passing around
a dubious and confusing 'adj_start' parameter along side a pointer to an
'adjust' VMA indicating which VMA requires additional adjustment (middle in
case 1 and next in case 2).
With the VMG structure in place we are able to avoid this by simply setting
a merge flag to describe each case:
(1) Sets the vmg->__adjust_middle_start flag
(2) Sets the vmg->__adjust_next_start flag
By doing so it turns out we can vastly simplify the logic and calculate
what is required to perform the operation.
Taken together the refactorings make it far easier to understand what is
being done even in these more confusing cases, make the code far more
maintainable, debuggable, and testable, providing more internal state
indicating what is happening in the merge operation.
The changes have no functional net impact on the merge operation and
everything should still behave as it did before.
v3:
* Fix seemingly compiler-version dependent printf() specifier formatter issue
in mm/debug.c per buildbot complaints.
v2:
* Fixed buildbot warnings due to missing a change to a static inline
stubbed out wrapper for vma_adjust_trans_huge().
* Converted vmg merge_flags to bitfield flags as per Vlastimil.
* Update comments which were rendered inaccurate in 5/5 as per Vlastimil.
https://lore.kernel.org/all/cover.1738172812.git.lorenzo.stoakes@oracle.com/
v1:
https://lore.kernel.org/all/cover.1737929364.git.lorenzo.stoakes@oracle.com/
Lorenzo Stoakes (5):
mm: simplify vma merge structure and expand comments
mm: further refactor commit_merge()
mm: eliminate adj_start parameter from commit_merge()
mm: make vmg->target consistent and further simplify commit_merge()
mm: completely abstract unnecessary adj_start calculation
include/linux/huge_mm.h | 4 +-
mm/debug.c | 28 +--
mm/huge_memory.c | 19 +-
mm/mmap.c | 2 +-
mm/vma.c | 327 ++++++++++++++++---------------
mm/vma.h | 86 ++++++--
tools/testing/vma/vma.c | 63 +++---
tools/testing/vma/vma_internal.h | 4 +-
8 files changed, 302 insertions(+), 231 deletions(-)
--
2.48.1
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH v3 1/5] mm: simplify vma merge structure and expand comments
2025-01-31 12:31 [PATCH v3 0/5] mm: further simplify VMA merge operation Lorenzo Stoakes
@ 2025-01-31 12:31 ` Lorenzo Stoakes
2025-01-31 12:31 ` [PATCH v3 2/5] mm: further refactor commit_merge() Lorenzo Stoakes
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: Lorenzo Stoakes @ 2025-01-31 12:31 UTC (permalink / raw)
To: Andrew Morton
Cc: Liam R . Howlett, Vlastimil Babka, Jann Horn, linux-mm, linux-kernel
The merge code, while much improved, still has a number of points of
confusion. As part of a broader series cleaning this up to make this more
maintainable, we start by addressing some confusion around vma_merge_struct
fields.
So far, the caller either provides no vmg->vma (a new VMA) or supplies the
existing VMA which is being altered, setting vmg->start,end,pgoff to the
proposed VMA dimensions.
vmg->vma is then updated, as are vmg->start,end,pgoff as the merge process
proceeds and the appropriate merge strategy is determined.
This is rather confusing, as vmg->vma starts off as the 'middle' VMA
between vmg->prev,next, but becomes the 'target' VMA, except in one
specific edge case (merge next, shrink middle).
Int his patch we introduce vmg->middle to describe the VMA that is between
vmg->prev and vmg->next, and does NOT change during the merge operation.
We replace vmg->vma with vmg->target, and use this only during the merge
operation itself.
Aside from the merge right, shrink middle case, this becomes the VMA that
forms the basis of the VMA that is returned. This edge case can be
addressed in a future commit.
We also add a number of comments to explain what is going on.
Finally, we adjust the ASCII diagrams showing each merge case in
vma_merge_existing_range() to be clearer - the arrow range previously
showed the vmg->start, end spanned area, but it is clearer to change this
to show the final merged VMA.
This patch has no change in functional behaviour.
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
---
mm/debug.c | 18 ++---
mm/mmap.c | 2 +-
mm/vma.c | 166 +++++++++++++++++++++-------------------
mm/vma.h | 42 ++++++++--
tools/testing/vma/vma.c | 52 ++++++-------
5 files changed, 159 insertions(+), 121 deletions(-)
diff --git a/mm/debug.c b/mm/debug.c
index 8d2acf432385..c9e07651677b 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -261,7 +261,7 @@ void dump_vmg(const struct vma_merge_struct *vmg, const char *reason)
pr_warn("vmg %px state: mm %px pgoff %lx\n"
"vmi %px [%lx,%lx)\n"
- "prev %px next %px vma %px\n"
+ "prev %px middle %px next %px target %px\n"
"start %lx end %lx flags %lx\n"
"file %px anon_vma %px policy %px\n"
"uffd_ctx %px\n"
@@ -270,7 +270,7 @@ void dump_vmg(const struct vma_merge_struct *vmg, const char *reason)
vmg, vmg->mm, vmg->pgoff,
vmg->vmi, vmg->vmi ? vma_iter_addr(vmg->vmi) : 0,
vmg->vmi ? vma_iter_end(vmg->vmi) : 0,
- vmg->prev, vmg->next, vmg->vma,
+ vmg->prev, vmg->middle, vmg->next, vmg->target,
vmg->start, vmg->end, vmg->flags,
vmg->file, vmg->anon_vma, vmg->policy,
#ifdef CONFIG_USERFAULTFD
@@ -288,13 +288,6 @@ void dump_vmg(const struct vma_merge_struct *vmg, const char *reason)
pr_warn("vmg %px mm: (NULL)\n", vmg);
}
- if (vmg->vma) {
- pr_warn("vmg %px vma:\n", vmg);
- dump_vma(vmg->vma);
- } else {
- pr_warn("vmg %px vma: (NULL)\n", vmg);
- }
-
if (vmg->prev) {
pr_warn("vmg %px prev:\n", vmg);
dump_vma(vmg->prev);
@@ -302,6 +295,13 @@ void dump_vmg(const struct vma_merge_struct *vmg, const char *reason)
pr_warn("vmg %px prev: (NULL)\n", vmg);
}
+ if (vmg->middle) {
+ pr_warn("vmg %px middle:\n", vmg);
+ dump_vma(vmg->middle);
+ } else {
+ pr_warn("vmg %px middle: (NULL)\n", vmg);
+ }
+
if (vmg->next) {
pr_warn("vmg %px next:\n", vmg);
dump_vma(vmg->next);
diff --git a/mm/mmap.c b/mm/mmap.c
index cda01071c7b1..6401a1d73f4a 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1707,7 +1707,7 @@ int relocate_vma_down(struct vm_area_struct *vma, unsigned long shift)
/*
* cover the whole range: [new_start, old_end)
*/
- vmg.vma = vma;
+ vmg.middle = vma;
if (vma_expand(&vmg))
return -ENOMEM;
diff --git a/mm/vma.c b/mm/vma.c
index af1d549b179c..68a301a76297 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -52,7 +52,7 @@ struct mmap_state {
.pgoff = (map_)->pgoff, \
.file = (map_)->file, \
.prev = (map_)->prev, \
- .vma = vma_, \
+ .middle = vma_, \
.next = (vma_) ? NULL : (map_)->next, \
.state = VMA_MERGE_START, \
.merge_flags = VMG_FLAG_DEFAULT, \
@@ -639,7 +639,7 @@ static int commit_merge(struct vma_merge_struct *vmg,
{
struct vma_prepare vp;
- init_multi_vma_prep(&vp, vmg->vma, adjust, remove, remove2);
+ init_multi_vma_prep(&vp, vmg->target, adjust, remove, remove2);
VM_WARN_ON(vp.anon_vma && adjust && adjust->anon_vma &&
vp.anon_vma != adjust->anon_vma);
@@ -652,15 +652,15 @@ static int commit_merge(struct vma_merge_struct *vmg,
adjust->vm_end);
}
- if (vma_iter_prealloc(vmg->vmi, vmg->vma))
+ if (vma_iter_prealloc(vmg->vmi, vmg->target))
return -ENOMEM;
vma_prepare(&vp);
- vma_adjust_trans_huge(vmg->vma, vmg->start, vmg->end, adj_start);
- vma_set_range(vmg->vma, vmg->start, vmg->end, vmg->pgoff);
+ vma_adjust_trans_huge(vmg->target, vmg->start, vmg->end, adj_start);
+ vma_set_range(vmg->target, vmg->start, vmg->end, vmg->pgoff);
if (expanded)
- vma_iter_store(vmg->vmi, vmg->vma);
+ vma_iter_store(vmg->vmi, vmg->target);
if (adj_start) {
adjust->vm_start += adj_start;
@@ -671,7 +671,7 @@ static int commit_merge(struct vma_merge_struct *vmg,
}
}
- vma_complete(&vp, vmg->vmi, vmg->vma->vm_mm);
+ vma_complete(&vp, vmg->vmi, vmg->target->vm_mm);
return 0;
}
@@ -694,8 +694,9 @@ static bool can_merge_remove_vma(struct vm_area_struct *vma)
* identical properties.
*
* This function checks for the existence of any such mergeable VMAs and updates
- * the maple tree describing the @vmg->vma->vm_mm address space to account for
- * this, as well as any VMAs shrunk/expanded/deleted as a result of this merge.
+ * the maple tree describing the @vmg->middle->vm_mm address space to account
+ * for this, as well as any VMAs shrunk/expanded/deleted as a result of this
+ * merge.
*
* As part of this operation, if a merge occurs, the @vmg object will have its
* vma, start, end, and pgoff fields modified to execute the merge. Subsequent
@@ -704,45 +705,47 @@ static bool can_merge_remove_vma(struct vm_area_struct *vma)
* Returns: The merged VMA if merge succeeds, or NULL otherwise.
*
* ASSUMPTIONS:
- * - The caller must assign the VMA to be modifed to @vmg->vma.
+ * - The caller must assign the VMA to be modifed to @vmg->middle.
* - The caller must have set @vmg->prev to the previous VMA, if there is one.
* - The caller must not set @vmg->next, as we determine this.
* - The caller must hold a WRITE lock on the mm_struct->mmap_lock.
- * - vmi must be positioned within [@vmg->vma->vm_start, @vmg->vma->vm_end).
+ * - vmi must be positioned within [@vmg->middle->vm_start, @vmg->middle->vm_end).
*/
static __must_check struct vm_area_struct *vma_merge_existing_range(
struct vma_merge_struct *vmg)
{
- struct vm_area_struct *vma = vmg->vma;
+ struct vm_area_struct *middle = vmg->middle;
struct vm_area_struct *prev = vmg->prev;
struct vm_area_struct *next, *res;
struct vm_area_struct *anon_dup = NULL;
struct vm_area_struct *adjust = NULL;
unsigned long start = vmg->start;
unsigned long end = vmg->end;
- bool left_side = vma && start == vma->vm_start;
- bool right_side = vma && end == vma->vm_end;
+ bool left_side = middle && start == middle->vm_start;
+ bool right_side = middle && end == middle->vm_end;
int err = 0;
long adj_start = 0;
- bool merge_will_delete_vma, merge_will_delete_next;
+ bool merge_will_delete_middle, merge_will_delete_next;
bool merge_left, merge_right, merge_both;
bool expanded;
mmap_assert_write_locked(vmg->mm);
- VM_WARN_ON_VMG(!vma, vmg); /* We are modifying a VMA, so caller must specify. */
+ VM_WARN_ON_VMG(!middle, vmg); /* We are modifying a VMA, so caller must specify. */
VM_WARN_ON_VMG(vmg->next, vmg); /* We set this. */
VM_WARN_ON_VMG(prev && start <= prev->vm_start, vmg);
VM_WARN_ON_VMG(start >= end, vmg);
/*
- * If vma == prev, then we are offset into a VMA. Otherwise, if we are
+ * If middle == prev, then we are offset into a VMA. Otherwise, if we are
* not, we must span a portion of the VMA.
*/
- VM_WARN_ON_VMG(vma && ((vma != prev && vmg->start != vma->vm_start) ||
- vmg->end > vma->vm_end), vmg);
- /* The vmi must be positioned within vmg->vma. */
- VM_WARN_ON_VMG(vma && !(vma_iter_addr(vmg->vmi) >= vma->vm_start &&
- vma_iter_addr(vmg->vmi) < vma->vm_end), vmg);
+ VM_WARN_ON_VMG(middle &&
+ ((middle != prev && vmg->start != middle->vm_start) ||
+ vmg->end > middle->vm_end), vmg);
+ /* The vmi must be positioned within vmg->middle. */
+ VM_WARN_ON_VMG(middle &&
+ !(vma_iter_addr(vmg->vmi) >= middle->vm_start &&
+ vma_iter_addr(vmg->vmi) < middle->vm_end), vmg);
vmg->state = VMA_MERGE_NOMERGE;
@@ -776,13 +779,13 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
merge_both = merge_left && merge_right;
/* If we span the entire VMA, a merge implies it will be deleted. */
- merge_will_delete_vma = left_side && right_side;
+ merge_will_delete_middle = left_side && right_side;
/*
- * If we need to remove vma in its entirety but are unable to do so,
+ * If we need to remove middle in its entirety but are unable to do so,
* we have no sensible recourse but to abort the merge.
*/
- if (merge_will_delete_vma && !can_merge_remove_vma(vma))
+ if (merge_will_delete_middle && !can_merge_remove_vma(middle))
return NULL;
/*
@@ -793,7 +796,7 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
/*
* If we cannot delete next, then we can reduce the operation to merging
- * prev and vma (thereby deleting vma).
+ * prev and middle (thereby deleting middle).
*/
if (merge_will_delete_next && !can_merge_remove_vma(next)) {
merge_will_delete_next = false;
@@ -801,8 +804,8 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
merge_both = false;
}
- /* No matter what happens, we will be adjusting vma. */
- vma_start_write(vma);
+ /* No matter what happens, we will be adjusting middle. */
+ vma_start_write(middle);
if (merge_left)
vma_start_write(prev);
@@ -812,13 +815,13 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
if (merge_both) {
/*
- * |<----->|
- * |-------*********-------|
- * prev vma next
- * extend delete delete
+ * |<-------------------->|
+ * |-------********-------|
+ * prev middle next
+ * extend delete delete
*/
- vmg->vma = prev;
+ vmg->target = prev;
vmg->start = prev->vm_start;
vmg->end = next->vm_end;
vmg->pgoff = prev->vm_pgoff;
@@ -826,78 +829,79 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
/*
* We already ensured anon_vma compatibility above, so now it's
* simply a case of, if prev has no anon_vma object, which of
- * next or vma contains the anon_vma we must duplicate.
+ * next or middle contains the anon_vma we must duplicate.
*/
- err = dup_anon_vma(prev, next->anon_vma ? next : vma, &anon_dup);
+ err = dup_anon_vma(prev, next->anon_vma ? next : middle,
+ &anon_dup);
} else if (merge_left) {
/*
- * |<----->| OR
- * |<--------->|
+ * |<------------>| OR
+ * |<----------------->|
* |-------*************
- * prev vma
+ * prev middle
* extend shrink/delete
*/
- vmg->vma = prev;
+ vmg->target = prev;
vmg->start = prev->vm_start;
vmg->pgoff = prev->vm_pgoff;
- if (!merge_will_delete_vma) {
- adjust = vma;
- adj_start = vmg->end - vma->vm_start;
+ if (!merge_will_delete_middle) {
+ adjust = middle;
+ adj_start = vmg->end - middle->vm_start;
}
- err = dup_anon_vma(prev, vma, &anon_dup);
+ err = dup_anon_vma(prev, middle, &anon_dup);
} else { /* merge_right */
/*
- * |<----->| OR
- * |<--------->|
+ * |<------------->| OR
+ * |<----------------->|
* *************-------|
- * vma next
+ * middle next
* shrink/delete extend
*/
pgoff_t pglen = PHYS_PFN(vmg->end - vmg->start);
VM_WARN_ON_VMG(!merge_right, vmg);
- /* If we are offset into a VMA, then prev must be vma. */
- VM_WARN_ON_VMG(vmg->start > vma->vm_start && prev && vma != prev, vmg);
+ /* If we are offset into a VMA, then prev must be middle. */
+ VM_WARN_ON_VMG(vmg->start > middle->vm_start && prev && middle != prev, vmg);
- if (merge_will_delete_vma) {
- vmg->vma = next;
+ if (merge_will_delete_middle) {
+ vmg->target = next;
vmg->end = next->vm_end;
vmg->pgoff = next->vm_pgoff - pglen;
} else {
/*
- * We shrink vma and expand next.
+ * We shrink middle and expand next.
*
* IMPORTANT: This is the ONLY case where the final
- * merged VMA is NOT vmg->vma, but rather vmg->next.
+ * merged VMA is NOT vmg->target, but rather vmg->next.
*/
-
- vmg->start = vma->vm_start;
+ vmg->target = middle;
+ vmg->start = middle->vm_start;
vmg->end = start;
- vmg->pgoff = vma->vm_pgoff;
+ vmg->pgoff = middle->vm_pgoff;
adjust = next;
- adj_start = -(vma->vm_end - start);
+ adj_start = -(middle->vm_end - start);
}
- err = dup_anon_vma(next, vma, &anon_dup);
+ err = dup_anon_vma(next, middle, &anon_dup);
}
if (err)
goto abort;
/*
- * In nearly all cases, we expand vmg->vma. There is one exception -
+ * In nearly all cases, we expand vmg->middle. There is one exception -
* merge_right where we partially span the VMA. In this case we shrink
- * the end of vmg->vma and adjust the start of vmg->next accordingly.
+ * the end of vmg->middle and adjust the start of vmg->next accordingly.
*/
- expanded = !merge_right || merge_will_delete_vma;
+ expanded = !merge_right || merge_will_delete_middle;
if (commit_merge(vmg, adjust,
- merge_will_delete_vma ? vma : NULL,
+ merge_will_delete_middle ? middle : NULL,
merge_will_delete_next ? next : NULL,
adj_start, expanded)) {
if (anon_dup)
@@ -973,7 +977,7 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg)
bool just_expand = vmg->merge_flags & VMG_FLAG_JUST_EXPAND;
mmap_assert_write_locked(vmg->mm);
- VM_WARN_ON_VMG(vmg->vma, vmg);
+ VM_WARN_ON_VMG(vmg->middle, vmg);
/* vmi must point at or before the gap. */
VM_WARN_ON_VMG(vma_iter_addr(vmg->vmi) > end, vmg);
@@ -989,13 +993,13 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg)
/* If we can merge with the next VMA, adjust vmg accordingly. */
if (can_merge_right) {
vmg->end = next->vm_end;
- vmg->vma = next;
+ vmg->middle = next;
}
/* If we can merge with the previous VMA, adjust vmg accordingly. */
if (can_merge_left) {
vmg->start = prev->vm_start;
- vmg->vma = prev;
+ vmg->middle = prev;
vmg->pgoff = prev->vm_pgoff;
/*
@@ -1017,10 +1021,10 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg)
* Now try to expand adjacent VMA(s). This takes care of removing the
* following VMA if we have VMAs on both sides.
*/
- if (vmg->vma && !vma_expand(vmg)) {
- khugepaged_enter_vma(vmg->vma, vmg->flags);
+ if (vmg->middle && !vma_expand(vmg)) {
+ khugepaged_enter_vma(vmg->middle, vmg->flags);
vmg->state = VMA_MERGE_SUCCESS;
- return vmg->vma;
+ return vmg->middle;
}
return NULL;
@@ -1032,44 +1036,46 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg)
* @vmg: Describes a VMA expansion operation.
*
* Expand @vma to vmg->start and vmg->end. Can expand off the start and end.
- * Will expand over vmg->next if it's different from vmg->vma and vmg->end ==
- * vmg->next->vm_end. Checking if the vmg->vma can expand and merge with
+ * Will expand over vmg->next if it's different from vmg->middle and vmg->end ==
+ * vmg->next->vm_end. Checking if the vmg->middle can expand and merge with
* vmg->next needs to be handled by the caller.
*
* Returns: 0 on success.
*
* ASSUMPTIONS:
- * - The caller must hold a WRITE lock on vmg->vma->mm->mmap_lock.
- * - The caller must have set @vmg->vma and @vmg->next.
+ * - The caller must hold a WRITE lock on vmg->middle->mm->mmap_lock.
+ * - The caller must have set @vmg->middle and @vmg->next.
*/
int vma_expand(struct vma_merge_struct *vmg)
{
struct vm_area_struct *anon_dup = NULL;
bool remove_next = false;
- struct vm_area_struct *vma = vmg->vma;
+ struct vm_area_struct *middle = vmg->middle;
struct vm_area_struct *next = vmg->next;
mmap_assert_write_locked(vmg->mm);
- vma_start_write(vma);
- if (next && (vma != next) && (vmg->end == next->vm_end)) {
+ vma_start_write(middle);
+ if (next && (middle != next) && (vmg->end == next->vm_end)) {
int ret;
remove_next = true;
/* This should already have been checked by this point. */
VM_WARN_ON_VMG(!can_merge_remove_vma(next), vmg);
vma_start_write(next);
- ret = dup_anon_vma(vma, next, &anon_dup);
+ ret = dup_anon_vma(middle, next, &anon_dup);
if (ret)
return ret;
}
/* Not merging but overwriting any part of next is not handled. */
VM_WARN_ON_VMG(next && !remove_next &&
- next != vma && vmg->end > next->vm_start, vmg);
+ next != middle && vmg->end > next->vm_start, vmg);
/* Only handles expanding */
- VM_WARN_ON_VMG(vma->vm_start < vmg->start || vma->vm_end > vmg->end, vmg);
+ VM_WARN_ON_VMG(middle->vm_start < vmg->start ||
+ middle->vm_end > vmg->end, vmg);
+ vmg->target = middle;
if (commit_merge(vmg, NULL, remove_next ? next : NULL, NULL, 0, true))
goto nomem;
@@ -1508,7 +1514,7 @@ int do_vmi_munmap(struct vma_iterator *vmi, struct mm_struct *mm,
*/
static struct vm_area_struct *vma_modify(struct vma_merge_struct *vmg)
{
- struct vm_area_struct *vma = vmg->vma;
+ struct vm_area_struct *vma = vmg->middle;
struct vm_area_struct *merged;
/* First, try to merge. */
@@ -1605,7 +1611,7 @@ struct vm_area_struct *vma_merge_extend(struct vma_iterator *vmi,
VMG_VMA_STATE(vmg, vmi, vma, vma, vma->vm_end, vma->vm_end + delta);
vmg.next = vma_iter_next_rewind(vmi, NULL);
- vmg.vma = NULL; /* We use the VMA to populate VMG fields only. */
+ vmg.middle = NULL; /* We use the VMA to populate VMG fields only. */
return vma_merge_new_range(&vmg);
}
@@ -1726,7 +1732,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
if (new_vma && new_vma->vm_start < addr + len)
return NULL; /* should never get here */
- vmg.vma = NULL; /* New VMA range. */
+ vmg.middle = NULL; /* New VMA range. */
vmg.pgoff = pgoff;
vmg.next = vma_iter_next_rewind(&vmi, NULL);
new_vma = vma_merge_new_range(&vmg);
diff --git a/mm/vma.h b/mm/vma.h
index a2e8710b8c47..5b5dd07e478c 100644
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -69,16 +69,48 @@ enum vma_merge_flags {
VMG_FLAG_JUST_EXPAND = 1 << 0,
};
-/* Represents a VMA merge operation. */
+/*
+ * Describes a VMA merge operation and is threaded throughout it.
+ *
+ * Any of the fields may be mutated by the merge operation, so no guarantees are
+ * made to the contents of this structure after a merge operation has completed.
+ */
struct vma_merge_struct {
struct mm_struct *mm;
struct vma_iterator *vmi;
- pgoff_t pgoff;
+ /*
+ * Adjacent VMAs, any of which may be NULL if not present:
+ *
+ * |------|--------|------|
+ * | prev | middle | next |
+ * |------|--------|------|
+ *
+ * middle may not yet exist in the case of a proposed new VMA being
+ * merged, or it may be an existing VMA.
+ *
+ * next may be assigned by the caller.
+ */
struct vm_area_struct *prev;
- struct vm_area_struct *next; /* Modified by vma_merge(). */
- struct vm_area_struct *vma; /* Either a new VMA or the one being modified. */
+ struct vm_area_struct *middle;
+ struct vm_area_struct *next;
+ /*
+ * This is the VMA we ultimately target to become the merged VMA, except
+ * for the one exception of merge right, shrink next (for details of
+ * this scenario see vma_merge_existing_range()).
+ */
+ struct vm_area_struct *target;
+ /*
+ * Initially, the start, end, pgoff fields are provided by the caller
+ * and describe the proposed new VMA range, whether modifying an
+ * existing VMA (which will be 'middle'), or adding a new one.
+ *
+ * During the merge process these fields are updated to describe the new
+ * range _including those VMAs which will be merged_.
+ */
unsigned long start;
unsigned long end;
+ pgoff_t pgoff;
+
unsigned long flags;
struct file *file;
struct anon_vma *anon_vma;
@@ -118,8 +150,8 @@ static inline pgoff_t vma_pgoff_offset(struct vm_area_struct *vma,
.mm = vma_->vm_mm, \
.vmi = vmi_, \
.prev = prev_, \
+ .middle = vma_, \
.next = NULL, \
- .vma = vma_, \
.start = start_, \
.end = end_, \
.flags = vma_->vm_flags, \
diff --git a/tools/testing/vma/vma.c b/tools/testing/vma/vma.c
index 04ab45e27fb8..3c0572120e94 100644
--- a/tools/testing/vma/vma.c
+++ b/tools/testing/vma/vma.c
@@ -147,8 +147,8 @@ static void vmg_set_range(struct vma_merge_struct *vmg, unsigned long start,
vma_iter_set(vmg->vmi, start);
vmg->prev = NULL;
+ vmg->middle = NULL;
vmg->next = NULL;
- vmg->vma = NULL;
vmg->start = start;
vmg->end = end;
@@ -338,7 +338,7 @@ static bool test_simple_expand(void)
VMA_ITERATOR(vmi, &mm, 0);
struct vma_merge_struct vmg = {
.vmi = &vmi,
- .vma = vma,
+ .middle = vma,
.start = 0,
.end = 0x3000,
.pgoff = 0,
@@ -631,7 +631,7 @@ static bool test_vma_merge_special_flags(void)
*/
vma = alloc_and_link_vma(&mm, 0x3000, 0x4000, 3, flags);
ASSERT_NE(vma, NULL);
- vmg.vma = vma;
+ vmg.middle = vma;
for (i = 0; i < ARRAY_SIZE(special_flags); i++) {
vm_flags_t special_flag = special_flags[i];
@@ -760,7 +760,7 @@ static bool test_vma_merge_with_close(void)
vmg_set_range(&vmg, 0x3000, 0x5000, 3, flags);
vmg.prev = vma_prev;
- vmg.vma = vma;
+ vmg.middle = vma;
/*
* The VMA being modified in a way that would otherwise merge should
@@ -787,7 +787,7 @@ static bool test_vma_merge_with_close(void)
vma->vm_ops = &vm_ops;
vmg_set_range(&vmg, 0x3000, 0x5000, 3, flags);
- vmg.vma = vma;
+ vmg.middle = vma;
ASSERT_EQ(merge_existing(&vmg), NULL);
/*
* Initially this is misapprehended as an out of memory report, as the
@@ -817,7 +817,7 @@ static bool test_vma_merge_with_close(void)
vmg_set_range(&vmg, 0x3000, 0x5000, 3, flags);
vmg.prev = vma_prev;
- vmg.vma = vma;
+ vmg.middle = vma;
ASSERT_EQ(merge_existing(&vmg), NULL);
ASSERT_EQ(vmg.state, VMA_MERGE_NOMERGE);
@@ -843,7 +843,7 @@ static bool test_vma_merge_with_close(void)
vmg_set_range(&vmg, 0x3000, 0x5000, 3, flags);
vmg.prev = vma_prev;
- vmg.vma = vma;
+ vmg.middle = vma;
ASSERT_EQ(merge_existing(&vmg), vma_prev);
ASSERT_EQ(vmg.state, VMA_MERGE_SUCCESS);
@@ -940,7 +940,7 @@ static bool test_merge_existing(void)
vma_next = alloc_and_link_vma(&mm, 0x6000, 0x9000, 6, flags);
vma_next->vm_ops = &vm_ops; /* This should have no impact. */
vmg_set_range(&vmg, 0x3000, 0x6000, 3, flags);
- vmg.vma = vma;
+ vmg.middle = vma;
vmg.prev = vma;
vma->anon_vma = &dummy_anon_vma;
ASSERT_EQ(merge_existing(&vmg), vma_next);
@@ -973,7 +973,7 @@ static bool test_merge_existing(void)
vma_next = alloc_and_link_vma(&mm, 0x6000, 0x9000, 6, flags);
vma_next->vm_ops = &vm_ops; /* This should have no impact. */
vmg_set_range(&vmg, 0x2000, 0x6000, 2, flags);
- vmg.vma = vma;
+ vmg.middle = vma;
vma->anon_vma = &dummy_anon_vma;
ASSERT_EQ(merge_existing(&vmg), vma_next);
ASSERT_EQ(vmg.state, VMA_MERGE_SUCCESS);
@@ -1003,7 +1003,7 @@ static bool test_merge_existing(void)
vma->vm_ops = &vm_ops; /* This should have no impact. */
vmg_set_range(&vmg, 0x3000, 0x6000, 3, flags);
vmg.prev = vma_prev;
- vmg.vma = vma;
+ vmg.middle = vma;
vma->anon_vma = &dummy_anon_vma;
ASSERT_EQ(merge_existing(&vmg), vma_prev);
@@ -1037,7 +1037,7 @@ static bool test_merge_existing(void)
vma = alloc_and_link_vma(&mm, 0x3000, 0x7000, 3, flags);
vmg_set_range(&vmg, 0x3000, 0x7000, 3, flags);
vmg.prev = vma_prev;
- vmg.vma = vma;
+ vmg.middle = vma;
vma->anon_vma = &dummy_anon_vma;
ASSERT_EQ(merge_existing(&vmg), vma_prev);
ASSERT_EQ(vmg.state, VMA_MERGE_SUCCESS);
@@ -1067,7 +1067,7 @@ static bool test_merge_existing(void)
vma_next = alloc_and_link_vma(&mm, 0x7000, 0x9000, 7, flags);
vmg_set_range(&vmg, 0x3000, 0x7000, 3, flags);
vmg.prev = vma_prev;
- vmg.vma = vma;
+ vmg.middle = vma;
vma->anon_vma = &dummy_anon_vma;
ASSERT_EQ(merge_existing(&vmg), vma_prev);
ASSERT_EQ(vmg.state, VMA_MERGE_SUCCESS);
@@ -1102,37 +1102,37 @@ static bool test_merge_existing(void)
vmg_set_range(&vmg, 0x4000, 0x5000, 4, flags);
vmg.prev = vma;
- vmg.vma = vma;
+ vmg.middle = vma;
ASSERT_EQ(merge_existing(&vmg), NULL);
ASSERT_EQ(vmg.state, VMA_MERGE_NOMERGE);
vmg_set_range(&vmg, 0x5000, 0x6000, 5, flags);
vmg.prev = vma;
- vmg.vma = vma;
+ vmg.middle = vma;
ASSERT_EQ(merge_existing(&vmg), NULL);
ASSERT_EQ(vmg.state, VMA_MERGE_NOMERGE);
vmg_set_range(&vmg, 0x6000, 0x7000, 6, flags);
vmg.prev = vma;
- vmg.vma = vma;
+ vmg.middle = vma;
ASSERT_EQ(merge_existing(&vmg), NULL);
ASSERT_EQ(vmg.state, VMA_MERGE_NOMERGE);
vmg_set_range(&vmg, 0x4000, 0x7000, 4, flags);
vmg.prev = vma;
- vmg.vma = vma;
+ vmg.middle = vma;
ASSERT_EQ(merge_existing(&vmg), NULL);
ASSERT_EQ(vmg.state, VMA_MERGE_NOMERGE);
vmg_set_range(&vmg, 0x4000, 0x6000, 4, flags);
vmg.prev = vma;
- vmg.vma = vma;
+ vmg.middle = vma;
ASSERT_EQ(merge_existing(&vmg), NULL);
ASSERT_EQ(vmg.state, VMA_MERGE_NOMERGE);
vmg_set_range(&vmg, 0x5000, 0x6000, 5, flags);
vmg.prev = vma;
- vmg.vma = vma;
+ vmg.middle = vma;
ASSERT_EQ(merge_existing(&vmg), NULL);
ASSERT_EQ(vmg.state, VMA_MERGE_NOMERGE);
@@ -1197,7 +1197,7 @@ static bool test_anon_vma_non_mergeable(void)
vmg_set_range(&vmg, 0x3000, 0x7000, 3, flags);
vmg.prev = vma_prev;
- vmg.vma = vma;
+ vmg.middle = vma;
ASSERT_EQ(merge_existing(&vmg), vma_prev);
ASSERT_EQ(vmg.state, VMA_MERGE_SUCCESS);
@@ -1277,7 +1277,7 @@ static bool test_dup_anon_vma(void)
vma_next->anon_vma = &dummy_anon_vma;
vmg_set_range(&vmg, 0, 0x5000, 0, flags);
- vmg.vma = vma_prev;
+ vmg.middle = vma_prev;
vmg.next = vma_next;
ASSERT_EQ(expand_existing(&vmg), 0);
@@ -1309,7 +1309,7 @@ static bool test_dup_anon_vma(void)
vma_next->anon_vma = &dummy_anon_vma;
vmg_set_range(&vmg, 0x3000, 0x5000, 3, flags);
vmg.prev = vma_prev;
- vmg.vma = vma;
+ vmg.middle = vma;
ASSERT_EQ(merge_existing(&vmg), vma_prev);
ASSERT_EQ(vmg.state, VMA_MERGE_SUCCESS);
@@ -1338,7 +1338,7 @@ static bool test_dup_anon_vma(void)
vma->anon_vma = &dummy_anon_vma;
vmg_set_range(&vmg, 0x3000, 0x5000, 3, flags);
vmg.prev = vma_prev;
- vmg.vma = vma;
+ vmg.middle = vma;
ASSERT_EQ(merge_existing(&vmg), vma_prev);
ASSERT_EQ(vmg.state, VMA_MERGE_SUCCESS);
@@ -1366,7 +1366,7 @@ static bool test_dup_anon_vma(void)
vma->anon_vma = &dummy_anon_vma;
vmg_set_range(&vmg, 0x3000, 0x5000, 3, flags);
vmg.prev = vma_prev;
- vmg.vma = vma;
+ vmg.middle = vma;
ASSERT_EQ(merge_existing(&vmg), vma_prev);
ASSERT_EQ(vmg.state, VMA_MERGE_SUCCESS);
@@ -1394,7 +1394,7 @@ static bool test_dup_anon_vma(void)
vma->anon_vma = &dummy_anon_vma;
vmg_set_range(&vmg, 0x3000, 0x5000, 3, flags);
vmg.prev = vma;
- vmg.vma = vma;
+ vmg.middle = vma;
ASSERT_EQ(merge_existing(&vmg), vma_next);
ASSERT_EQ(vmg.state, VMA_MERGE_SUCCESS);
@@ -1432,7 +1432,7 @@ static bool test_vmi_prealloc_fail(void)
vmg_set_range(&vmg, 0x3000, 0x5000, 3, flags);
vmg.prev = vma_prev;
- vmg.vma = vma;
+ vmg.middle = vma;
fail_prealloc = true;
@@ -1458,7 +1458,7 @@ static bool test_vmi_prealloc_fail(void)
vma->anon_vma = &dummy_anon_vma;
vmg_set_range(&vmg, 0, 0x5000, 3, flags);
- vmg.vma = vma_prev;
+ vmg.middle = vma_prev;
vmg.next = vma;
fail_prealloc = true;
--
2.48.1
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH v3 2/5] mm: further refactor commit_merge()
2025-01-31 12:31 [PATCH v3 0/5] mm: further simplify VMA merge operation Lorenzo Stoakes
2025-01-31 12:31 ` [PATCH v3 1/5] mm: simplify vma merge structure and expand comments Lorenzo Stoakes
@ 2025-01-31 12:31 ` Lorenzo Stoakes
2025-01-31 12:31 ` [PATCH v3 3/5] mm: eliminate adj_start parameter from commit_merge() Lorenzo Stoakes
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: Lorenzo Stoakes @ 2025-01-31 12:31 UTC (permalink / raw)
To: Andrew Morton
Cc: Liam R . Howlett, Vlastimil Babka, Jann Horn, linux-mm, linux-kernel
The current VMA merge mechanism contains a number of confusing mechanisms
around removal of VMAs on merge and the shrinking of the VMA adjacent to
vma->target in the case of merges which result in a partial merge with that
adjacent VMA.
Since we now have a STABLE set of VMAs - prev, middle, next - we are now
able to have the caller of commit_merge() explicitly tell us which VMAs
need deleting, using newly introduced internal VMA merge flags.
Doing so allows us to embed this state within the VMG and remove the
confusing remove, remove2 parameters from commit_merge().
We additionally are able to eliminate the highly confusing and misleading
'expanded' parameter - a parameter that in reality refers to whether or not
the return VMA is the target one or the one immediately adjacent.
We can infer which is the case from whether or not the adj_start parameter
is negative. This also allows us to simplify further logic around iterator
configuration and VMA iterator stores.
Doing so means we can also eliminate the adjust parameter, as we are able
to infer which VMA ought to be adjusted from adj_start - a positive value
implies we adjust the start of 'middle', a negative one implies we adjust
the start of 'next'.
We are then able to have commit_merge() explicitly return the target VMA,
or NULL on inability to pre-allocate memory. Errors were previously
filtered so behaviour does not change.
We additionally move from the slightly odd use of a bitwise-flag enum
vmg->merge_flags field to vmg bitfields.
This patch has no change in functional behaviour.
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
---
mm/debug.c | 6 ++-
mm/vma.c | 101 +++++++++++++++++++++-------------------
mm/vma.h | 38 +++++++++------
tools/testing/vma/vma.c | 9 +++-
4 files changed, 87 insertions(+), 67 deletions(-)
diff --git a/mm/debug.c b/mm/debug.c
index c9e07651677b..60c6f1134383 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -266,7 +266,8 @@ void dump_vmg(const struct vma_merge_struct *vmg, const char *reason)
"file %px anon_vma %px policy %px\n"
"uffd_ctx %px\n"
"anon_name %px\n"
- "merge_flags %x state %x\n",
+ "state %x\n"
+ "just_expand %d __remove_middle %d __remove_next %d\n",
vmg, vmg->mm, vmg->pgoff,
vmg->vmi, vmg->vmi ? vma_iter_addr(vmg->vmi) : 0,
vmg->vmi ? vma_iter_end(vmg->vmi) : 0,
@@ -279,7 +280,8 @@ void dump_vmg(const struct vma_merge_struct *vmg, const char *reason)
(void *)0,
#endif
vmg->anon_name,
- (int)vmg->merge_flags, (int)vmg->state);
+ (int)vmg->state,
+ vmg->just_expand, vmg->__remove_middle, vmg->__remove_next);
if (vmg->mm) {
pr_warn("vmg %px mm:\n", vmg);
diff --git a/mm/vma.c b/mm/vma.c
index 68a301a76297..206e3523cf38 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -55,7 +55,6 @@ struct mmap_state {
.middle = vma_, \
.next = (vma_) ? NULL : (map_)->next, \
.state = VMA_MERGE_START, \
- .merge_flags = VMG_FLAG_DEFAULT, \
}
static inline bool is_mergeable_vma(struct vma_merge_struct *vmg, bool merge_next)
@@ -120,8 +119,8 @@ static void init_multi_vma_prep(struct vma_prepare *vp,
memset(vp, 0, sizeof(struct vma_prepare));
vp->vma = vma;
vp->anon_vma = vma->anon_vma;
- vp->remove = remove;
- vp->remove2 = remove2;
+ vp->remove = remove ? remove : remove2;
+ vp->remove2 = remove ? remove2 : NULL;
vp->adj_next = next;
if (!vp->anon_vma && next)
vp->anon_vma = next->anon_vma;
@@ -129,7 +128,6 @@ static void init_multi_vma_prep(struct vma_prepare *vp,
vp->file = vma->vm_file;
if (vp->file)
vp->mapping = vma->vm_file->f_mapping;
-
}
/*
@@ -629,22 +627,40 @@ void validate_mm(struct mm_struct *mm)
}
#endif /* CONFIG_DEBUG_VM_MAPLE_TREE */
-/* Actually perform the VMA merge operation. */
-static int commit_merge(struct vma_merge_struct *vmg,
- struct vm_area_struct *adjust,
- struct vm_area_struct *remove,
- struct vm_area_struct *remove2,
- long adj_start,
- bool expanded)
+/*
+ * Actually perform the VMA merge operation.
+ *
+ * On success, returns the merged VMA. Otherwise returns NULL.
+ */
+static struct vm_area_struct *commit_merge(struct vma_merge_struct *vmg,
+ long adj_start)
{
struct vma_prepare vp;
+ struct vm_area_struct *remove = NULL;
+ struct vm_area_struct *remove2 = NULL;
+ struct vm_area_struct *adjust = NULL;
+ /*
+ * In all cases but that of merge right, shrink next, we write
+ * vmg->target to the maple tree and return this as the merged VMA.
+ */
+ bool merge_target = adj_start >= 0;
+
+ if (vmg->__remove_middle)
+ remove = vmg->middle;
+ if (vmg->__remove_next)
+ remove2 = vmg->next;
+
+ if (adj_start > 0)
+ adjust = vmg->middle;
+ else if (adj_start < 0)
+ adjust = vmg->next;
init_multi_vma_prep(&vp, vmg->target, adjust, remove, remove2);
VM_WARN_ON(vp.anon_vma && adjust && adjust->anon_vma &&
vp.anon_vma != adjust->anon_vma);
- if (expanded) {
+ if (merge_target) {
/* Note: vma iterator must be pointing to 'start'. */
vma_iter_config(vmg->vmi, vmg->start, vmg->end);
} else {
@@ -653,27 +669,26 @@ static int commit_merge(struct vma_merge_struct *vmg,
}
if (vma_iter_prealloc(vmg->vmi, vmg->target))
- return -ENOMEM;
+ return NULL;
vma_prepare(&vp);
vma_adjust_trans_huge(vmg->target, vmg->start, vmg->end, adj_start);
vma_set_range(vmg->target, vmg->start, vmg->end, vmg->pgoff);
- if (expanded)
+ if (merge_target)
vma_iter_store(vmg->vmi, vmg->target);
if (adj_start) {
adjust->vm_start += adj_start;
adjust->vm_pgoff += PHYS_PFN(adj_start);
- if (adj_start < 0) {
- WARN_ON(expanded);
+
+ if (!merge_target)
vma_iter_store(vmg->vmi, adjust);
- }
}
vma_complete(&vp, vmg->vmi, vmg->target->vm_mm);
- return 0;
+ return merge_target ? vmg->target : vmg->next;
}
/* We can only remove VMAs when merging if they do not have a close hook. */
@@ -718,16 +733,13 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
struct vm_area_struct *prev = vmg->prev;
struct vm_area_struct *next, *res;
struct vm_area_struct *anon_dup = NULL;
- struct vm_area_struct *adjust = NULL;
unsigned long start = vmg->start;
unsigned long end = vmg->end;
bool left_side = middle && start == middle->vm_start;
bool right_side = middle && end == middle->vm_end;
int err = 0;
long adj_start = 0;
- bool merge_will_delete_middle, merge_will_delete_next;
bool merge_left, merge_right, merge_both;
- bool expanded;
mmap_assert_write_locked(vmg->mm);
VM_WARN_ON_VMG(!middle, vmg); /* We are modifying a VMA, so caller must specify. */
@@ -779,27 +791,27 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
merge_both = merge_left && merge_right;
/* If we span the entire VMA, a merge implies it will be deleted. */
- merge_will_delete_middle = left_side && right_side;
+ vmg->__remove_middle = left_side && right_side;
/*
* If we need to remove middle in its entirety but are unable to do so,
* we have no sensible recourse but to abort the merge.
*/
- if (merge_will_delete_middle && !can_merge_remove_vma(middle))
+ if (vmg->__remove_middle && !can_merge_remove_vma(middle))
return NULL;
/*
* If we merge both VMAs, then next is also deleted. This implies
* merge_will_delete_vma also.
*/
- merge_will_delete_next = merge_both;
+ vmg->__remove_next = merge_both;
/*
* If we cannot delete next, then we can reduce the operation to merging
* prev and middle (thereby deleting middle).
*/
- if (merge_will_delete_next && !can_merge_remove_vma(next)) {
- merge_will_delete_next = false;
+ if (vmg->__remove_next && !can_merge_remove_vma(next)) {
+ vmg->__remove_next = false;
merge_right = false;
merge_both = false;
}
@@ -846,10 +858,11 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
vmg->start = prev->vm_start;
vmg->pgoff = prev->vm_pgoff;
- if (!merge_will_delete_middle) {
- adjust = middle;
+ /*
+ * We both expand prev and shrink middle.
+ */
+ if (!vmg->__remove_middle)
adj_start = vmg->end - middle->vm_start;
- }
err = dup_anon_vma(prev, middle, &anon_dup);
} else { /* merge_right */
@@ -867,7 +880,7 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
/* If we are offset into a VMA, then prev must be middle. */
VM_WARN_ON_VMG(vmg->start > middle->vm_start && prev && middle != prev, vmg);
- if (merge_will_delete_middle) {
+ if (vmg->__remove_middle) {
vmg->target = next;
vmg->end = next->vm_end;
vmg->pgoff = next->vm_pgoff - pglen;
@@ -883,7 +896,6 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
vmg->end = start;
vmg->pgoff = middle->vm_pgoff;
- adjust = next;
adj_start = -(middle->vm_end - start);
}
@@ -893,17 +905,8 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
if (err)
goto abort;
- /*
- * In nearly all cases, we expand vmg->middle. There is one exception -
- * merge_right where we partially span the VMA. In this case we shrink
- * the end of vmg->middle and adjust the start of vmg->next accordingly.
- */
- expanded = !merge_right || merge_will_delete_middle;
-
- if (commit_merge(vmg, adjust,
- merge_will_delete_middle ? middle : NULL,
- merge_will_delete_next ? next : NULL,
- adj_start, expanded)) {
+ res = commit_merge(vmg, adj_start);
+ if (!res) {
if (anon_dup)
unlink_anon_vmas(anon_dup);
@@ -911,9 +914,7 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
return NULL;
}
- res = merge_left ? prev : next;
khugepaged_enter_vma(res, vmg->flags);
-
vmg->state = VMA_MERGE_SUCCESS;
return res;
@@ -974,7 +975,6 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg)
struct vm_area_struct *next = vmg->next;
unsigned long end = vmg->end;
bool can_merge_left, can_merge_right;
- bool just_expand = vmg->merge_flags & VMG_FLAG_JUST_EXPAND;
mmap_assert_write_locked(vmg->mm);
VM_WARN_ON_VMG(vmg->middle, vmg);
@@ -988,7 +988,7 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg)
return NULL;
can_merge_left = can_vma_merge_left(vmg);
- can_merge_right = !just_expand && can_vma_merge_right(vmg, can_merge_left);
+ can_merge_right = !vmg->just_expand && can_vma_merge_right(vmg, can_merge_left);
/* If we can merge with the next VMA, adjust vmg accordingly. */
if (can_merge_right) {
@@ -1011,7 +1011,7 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg)
vmg->end = end;
/* In expand-only case we are already positioned at prev. */
- if (!just_expand) {
+ if (!vmg->just_expand) {
/* Equivalent to going to the previous range. */
vma_prev(vmg->vmi);
}
@@ -1076,7 +1076,10 @@ int vma_expand(struct vma_merge_struct *vmg)
middle->vm_end > vmg->end, vmg);
vmg->target = middle;
- if (commit_merge(vmg, NULL, remove_next ? next : NULL, NULL, 0, true))
+ if (remove_next)
+ vmg->__remove_next = true;
+
+ if (!commit_merge(vmg, 0))
goto nomem;
return 0;
@@ -2588,7 +2591,7 @@ int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,
vmg.prev = vma;
/* vmi is positioned at prev, which this mode expects. */
- vmg.merge_flags = VMG_FLAG_JUST_EXPAND;
+ vmg.just_expand = true;
if (vma_merge_new_range(&vmg))
goto out;
diff --git a/mm/vma.h b/mm/vma.h
index 5b5dd07e478c..7935681a2db8 100644
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -58,17 +58,6 @@ enum vma_merge_state {
VMA_MERGE_SUCCESS,
};
-enum vma_merge_flags {
- VMG_FLAG_DEFAULT = 0,
- /*
- * If we can expand, simply do so. We know there is nothing to merge to
- * the right. Does not reset state upon failure to merge. The VMA
- * iterator is assumed to be positioned at the previous VMA, rather than
- * at the gap.
- */
- VMG_FLAG_JUST_EXPAND = 1 << 0,
-};
-
/*
* Describes a VMA merge operation and is threaded throughout it.
*
@@ -117,8 +106,31 @@ struct vma_merge_struct {
struct mempolicy *policy;
struct vm_userfaultfd_ctx uffd_ctx;
struct anon_vma_name *anon_name;
- enum vma_merge_flags merge_flags;
enum vma_merge_state state;
+
+ /* Flags which callers can use to modify merge behaviour: */
+
+ /*
+ * If we can expand, simply do so. We know there is nothing to merge to
+ * the right. Does not reset state upon failure to merge. The VMA
+ * iterator is assumed to be positioned at the previous VMA, rather than
+ * at the gap.
+ */
+ bool just_expand :1;
+
+ /* Internal flags set during merge process: */
+
+ /*
+ * Internal flag used during the merge operation to indicate we will
+ * remove vmg->middle.
+ */
+ bool __remove_middle :1;
+ /*
+ * Internal flag used during the merge operationr to indicate we will
+ * remove vmg->next.
+ */
+ bool __remove_next :1;
+
};
static inline bool vmg_nomem(struct vma_merge_struct *vmg)
@@ -142,7 +154,6 @@ static inline pgoff_t vma_pgoff_offset(struct vm_area_struct *vma,
.flags = flags_, \
.pgoff = pgoff_, \
.state = VMA_MERGE_START, \
- .merge_flags = VMG_FLAG_DEFAULT, \
}
#define VMG_VMA_STATE(name, vmi_, prev_, vma_, start_, end_) \
@@ -162,7 +173,6 @@ static inline pgoff_t vma_pgoff_offset(struct vm_area_struct *vma,
.uffd_ctx = vma_->vm_userfaultfd_ctx, \
.anon_name = anon_vma_name(vma_), \
.state = VMA_MERGE_START, \
- .merge_flags = VMG_FLAG_DEFAULT, \
}
#ifdef CONFIG_DEBUG_VM_MAPLE_TREE
diff --git a/tools/testing/vma/vma.c b/tools/testing/vma/vma.c
index 3c0572120e94..7728498b2f7e 100644
--- a/tools/testing/vma/vma.c
+++ b/tools/testing/vma/vma.c
@@ -149,11 +149,16 @@ static void vmg_set_range(struct vma_merge_struct *vmg, unsigned long start,
vmg->prev = NULL;
vmg->middle = NULL;
vmg->next = NULL;
+ vmg->target = NULL;
vmg->start = start;
vmg->end = end;
vmg->pgoff = pgoff;
vmg->flags = flags;
+
+ vmg->just_expand = false;
+ vmg->__remove_middle = false;
+ vmg->__remove_next = false;
}
/*
@@ -1546,7 +1551,7 @@ static bool test_expand_only_mode(void)
/*
* Place a VMA prior to the one we're expanding so we assert that we do
* not erroneously try to traverse to the previous VMA even though we
- * have, through the use of VMG_FLAG_JUST_EXPAND, indicated we do not
+ * have, through the use of the just_expand flag, indicated we do not
* need to do so.
*/
alloc_and_link_vma(&mm, 0, 0x2000, 0, flags);
@@ -1558,7 +1563,7 @@ static bool test_expand_only_mode(void)
vma_iter_set(&vmi, 0x3000);
vma_prev = alloc_and_link_vma(&mm, 0x3000, 0x5000, 3, flags);
vmg.prev = vma_prev;
- vmg.merge_flags = VMG_FLAG_JUST_EXPAND;
+ vmg.just_expand = true;
vma = vma_merge_new_range(&vmg);
ASSERT_NE(vma, NULL);
--
2.48.1
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH v3 3/5] mm: eliminate adj_start parameter from commit_merge()
2025-01-31 12:31 [PATCH v3 0/5] mm: further simplify VMA merge operation Lorenzo Stoakes
2025-01-31 12:31 ` [PATCH v3 1/5] mm: simplify vma merge structure and expand comments Lorenzo Stoakes
2025-01-31 12:31 ` [PATCH v3 2/5] mm: further refactor commit_merge() Lorenzo Stoakes
@ 2025-01-31 12:31 ` Lorenzo Stoakes
2025-01-31 12:31 ` [PATCH v3 4/5] mm: make vmg->target consistent and further simplify commit_merge() Lorenzo Stoakes
2025-01-31 12:31 ` [PATCH v3 5/5] mm: completely abstract unnecessary adj_start calculation Lorenzo Stoakes
4 siblings, 0 replies; 6+ messages in thread
From: Lorenzo Stoakes @ 2025-01-31 12:31 UTC (permalink / raw)
To: Andrew Morton
Cc: Liam R . Howlett, Vlastimil Babka, Jann Horn, linux-mm, linux-kernel
Introduce internal vmg->__adjust_middle_start and vmg->__adjust_next_start
merge flags, enabling us to indicate to commit_merge() that we are
performing a merge which either spans only part of vmg->middle, or part of
vmg->next respectively.
In the former instance, we change the start of vmg->middle to match the
attributes of vmg->prev, without spanning all of vmg->middle.
This implies that vmg->prev->vm_end and vmg->middle->vm_start are both
increased to form the new merged VMA (vmg->prev) and the new subsequent VMA
(vmg->middle).
In the latter case, we change the end of vmg->middle to match the
attributes of vmg->next, without spanning all of vmg->next.
This implies that vmg->middle->vm_end and vmg->next->vm_start are both
decreased to form the new merged VMA (vmg->next) and the new prior VMA
(vmg->middle).
Since we now have a stable set of prev, middle, next VMAs threaded through
vmg and with these flags set know what is happening, we can perform
the calculation in commit_merge() instead.
This allows us to drop the confusing adj_start parameter and instead pass
semantic information to commit_merge().
In the latter case the -(middle->vm_end - start) calculation becomes
-(middle->vm-end - vmg->end), however this is correct as vmg->end is set to
the start parameter.
This is because in this case (rather confusingly), we manipulate
vmg->middle, but ultimately return vmg->next, whose range will be correctly
specified. At this point vmg->start, end is the new range for the prior VMA
rather than the merged one.
This patch has no change in functional behaviour.
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
---
mm/debug.c | 8 +++++--
mm/vma.c | 50 ++++++++++++++++++++++++-----------------
mm/vma.h | 10 +++++++++
tools/testing/vma/vma.c | 2 ++
4 files changed, 48 insertions(+), 22 deletions(-)
diff --git a/mm/debug.c b/mm/debug.c
index 60c6f1134383..e1282b85a877 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -267,7 +267,9 @@ void dump_vmg(const struct vma_merge_struct *vmg, const char *reason)
"uffd_ctx %px\n"
"anon_name %px\n"
"state %x\n"
- "just_expand %d __remove_middle %d __remove_next %d\n",
+ "just_expand %d\n"
+ "__adjust_middle_start %d __adjust_next_start %d\n"
+ "__remove_middle %d __remove_next %d\n",
vmg, vmg->mm, vmg->pgoff,
vmg->vmi, vmg->vmi ? vma_iter_addr(vmg->vmi) : 0,
vmg->vmi ? vma_iter_end(vmg->vmi) : 0,
@@ -281,7 +283,9 @@ void dump_vmg(const struct vma_merge_struct *vmg, const char *reason)
#endif
vmg->anon_name,
(int)vmg->state,
- vmg->just_expand, vmg->__remove_middle, vmg->__remove_next);
+ vmg->just_expand,
+ vmg->__adjust_middle_start, vmg->__adjust_next_start,
+ vmg->__remove_middle, vmg->__remove_next);
if (vmg->mm) {
pr_warn("vmg %px mm:\n", vmg);
diff --git a/mm/vma.c b/mm/vma.c
index 206e3523cf38..3fe264200b79 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -632,29 +632,44 @@ void validate_mm(struct mm_struct *mm)
*
* On success, returns the merged VMA. Otherwise returns NULL.
*/
-static struct vm_area_struct *commit_merge(struct vma_merge_struct *vmg,
- long adj_start)
+static struct vm_area_struct *commit_merge(struct vma_merge_struct *vmg)
{
- struct vma_prepare vp;
struct vm_area_struct *remove = NULL;
struct vm_area_struct *remove2 = NULL;
+ struct vma_prepare vp;
struct vm_area_struct *adjust = NULL;
+ long adj_start;
+ bool merge_target;
+
/*
- * In all cases but that of merge right, shrink next, we write
- * vmg->target to the maple tree and return this as the merged VMA.
+ * If modifying an existing VMA and we don't remove vmg->middle, then we
+ * shrink the adjacent VMA.
*/
- bool merge_target = adj_start >= 0;
+ if (vmg->__adjust_middle_start) {
+ adjust = vmg->middle;
+ /* The POSITIVE value by which we offset vmg->middle->vm_start. */
+ adj_start = vmg->end - vmg->middle->vm_start;
+ merge_target = true;
+ } else if (vmg->__adjust_next_start) {
+ adjust = vmg->next;
+ /* The NEGATIVE value by which we offset vmg->next->vm_start. */
+ adj_start = -(vmg->middle->vm_end - vmg->end);
+ /*
+ * In all cases but this - merge right, shrink next - we write
+ * vmg->target to the maple tree and return this as the merged VMA.
+ */
+ merge_target = false;
+ } else {
+ adjust = NULL;
+ adj_start = 0;
+ merge_target = true;
+ }
if (vmg->__remove_middle)
remove = vmg->middle;
if (vmg->__remove_next)
remove2 = vmg->next;
- if (adj_start > 0)
- adjust = vmg->middle;
- else if (adj_start < 0)
- adjust = vmg->next;
-
init_multi_vma_prep(&vp, vmg->target, adjust, remove, remove2);
VM_WARN_ON(vp.anon_vma && adjust && adjust->anon_vma &&
@@ -738,7 +753,6 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
bool left_side = middle && start == middle->vm_start;
bool right_side = middle && end == middle->vm_end;
int err = 0;
- long adj_start = 0;
bool merge_left, merge_right, merge_both;
mmap_assert_write_locked(vmg->mm);
@@ -858,11 +872,8 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
vmg->start = prev->vm_start;
vmg->pgoff = prev->vm_pgoff;
- /*
- * We both expand prev and shrink middle.
- */
if (!vmg->__remove_middle)
- adj_start = vmg->end - middle->vm_start;
+ vmg->__adjust_middle_start = true;
err = dup_anon_vma(prev, middle, &anon_dup);
} else { /* merge_right */
@@ -891,12 +902,11 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
* IMPORTANT: This is the ONLY case where the final
* merged VMA is NOT vmg->target, but rather vmg->next.
*/
+ vmg->__adjust_next_start = true;
vmg->target = middle;
vmg->start = middle->vm_start;
vmg->end = start;
vmg->pgoff = middle->vm_pgoff;
-
- adj_start = -(middle->vm_end - start);
}
err = dup_anon_vma(next, middle, &anon_dup);
@@ -905,7 +915,7 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
if (err)
goto abort;
- res = commit_merge(vmg, adj_start);
+ res = commit_merge(vmg);
if (!res) {
if (anon_dup)
unlink_anon_vmas(anon_dup);
@@ -1079,7 +1089,7 @@ int vma_expand(struct vma_merge_struct *vmg)
if (remove_next)
vmg->__remove_next = true;
- if (!commit_merge(vmg, 0))
+ if (!commit_merge(vmg))
goto nomem;
return 0;
diff --git a/mm/vma.h b/mm/vma.h
index 7935681a2db8..e18487797fa4 100644
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -120,6 +120,16 @@ struct vma_merge_struct {
/* Internal flags set during merge process: */
+ /*
+ * Internal flag indicating the merge increases vmg->middle->vm_start
+ * (and thereby, vmg->prev->vm_end).
+ */
+ bool __adjust_middle_start :1;
+ /*
+ * Internal flag indicating the merge decreases vmg->next->vm_start
+ * (and thereby, vmg->middle->vm_end).
+ */
+ bool __adjust_next_start :1;
/*
* Internal flag used during the merge operation to indicate we will
* remove vmg->middle.
diff --git a/tools/testing/vma/vma.c b/tools/testing/vma/vma.c
index 7728498b2f7e..c7ffa71841ca 100644
--- a/tools/testing/vma/vma.c
+++ b/tools/testing/vma/vma.c
@@ -159,6 +159,8 @@ static void vmg_set_range(struct vma_merge_struct *vmg, unsigned long start,
vmg->just_expand = false;
vmg->__remove_middle = false;
vmg->__remove_next = false;
+ vmg->__adjust_middle_start = false;
+ vmg->__adjust_next_start = false;
}
/*
--
2.48.1
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH v3 4/5] mm: make vmg->target consistent and further simplify commit_merge()
2025-01-31 12:31 [PATCH v3 0/5] mm: further simplify VMA merge operation Lorenzo Stoakes
` (2 preceding siblings ...)
2025-01-31 12:31 ` [PATCH v3 3/5] mm: eliminate adj_start parameter from commit_merge() Lorenzo Stoakes
@ 2025-01-31 12:31 ` Lorenzo Stoakes
2025-01-31 12:31 ` [PATCH v3 5/5] mm: completely abstract unnecessary adj_start calculation Lorenzo Stoakes
4 siblings, 0 replies; 6+ messages in thread
From: Lorenzo Stoakes @ 2025-01-31 12:31 UTC (permalink / raw)
To: Andrew Morton
Cc: Liam R . Howlett, Vlastimil Babka, Jann Horn, linux-mm, linux-kernel
It is confusing for vmg->target to sometimes be the target merged VMA and
in one case not.
Fix this by having commit_merge() use its awareness of the
vmg->_adjust_next_start case to know that it is manipulating a separate
vma, abstracted in the 'vma' local variable.
Place removal and adjust VMA determination logic into
init_multi_vma_prep(), as the flags give us enough information to do so,
and since this is the function that sets up the vma_prepare struct it makes
sense to do so here.
Doing this significantly simplifies commit_merge(), allowing us to
eliminate the 'merge_target' handling, initialise the VMA iterator in a
more sensible place and simply return vmg->target consistently.
This also allows us to simplify setting vmg->target in
vma_merge_existing_range() since we are then left only with two cases -
merge left (or both) where the target is vmg->prev or merge right in which
the target is vmg->next.
This makes it easy for somebody reading the code to know what VMA will
actually be the one returned and merged into and removes a great deal of
the confusing 'adjust' nonsense.
This patch has no change in functional behaviour.
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
---
mm/vma.c | 119 ++++++++++++++++++++++++++++---------------------------
mm/vma.h | 6 +--
2 files changed, 62 insertions(+), 63 deletions(-)
diff --git a/mm/vma.c b/mm/vma.c
index 3fe264200b79..75bbe82b2e65 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -106,24 +106,40 @@ static inline bool are_anon_vmas_compatible(struct vm_area_struct *vma1,
* init_multi_vma_prep() - Initializer for struct vma_prepare
* @vp: The vma_prepare struct
* @vma: The vma that will be altered once locked
- * @next: The next vma if it is to be adjusted
- * @remove: The first vma to be removed
- * @remove2: The second vma to be removed
+ * @vmg: The merge state that will be used to determine adjustment and VMA
+ * removal.
*/
static void init_multi_vma_prep(struct vma_prepare *vp,
struct vm_area_struct *vma,
- struct vm_area_struct *next,
- struct vm_area_struct *remove,
- struct vm_area_struct *remove2)
+ struct vma_merge_struct *vmg)
{
+ struct vm_area_struct *adjust;
+ struct vm_area_struct **remove = &vp->remove;
+
memset(vp, 0, sizeof(struct vma_prepare));
vp->vma = vma;
vp->anon_vma = vma->anon_vma;
- vp->remove = remove ? remove : remove2;
- vp->remove2 = remove ? remove2 : NULL;
- vp->adj_next = next;
- if (!vp->anon_vma && next)
- vp->anon_vma = next->anon_vma;
+
+ if (vmg && vmg->__remove_middle) {
+ *remove = vmg->middle;
+ remove = &vp->remove2;
+ }
+ if (vmg && vmg->__remove_next)
+ *remove = vmg->next;
+
+ if (vmg && vmg->__adjust_middle_start)
+ adjust = vmg->middle;
+ else if (vmg && vmg->__adjust_next_start)
+ adjust = vmg->next;
+ else
+ adjust = NULL;
+
+ vp->adj_next = adjust;
+ if (!vp->anon_vma && adjust)
+ vp->anon_vma = adjust->anon_vma;
+
+ VM_WARN_ON(vp->anon_vma && adjust && adjust->anon_vma &&
+ vp->anon_vma != adjust->anon_vma);
vp->file = vma->vm_file;
if (vp->file)
@@ -360,7 +376,7 @@ static void vma_complete(struct vma_prepare *vp, struct vma_iterator *vmi,
*/
static void init_vma_prep(struct vma_prepare *vp, struct vm_area_struct *vma)
{
- init_multi_vma_prep(vp, vma, NULL, NULL, NULL);
+ init_multi_vma_prep(vp, vma, NULL);
}
/*
@@ -634,76 +650,63 @@ void validate_mm(struct mm_struct *mm)
*/
static struct vm_area_struct *commit_merge(struct vma_merge_struct *vmg)
{
- struct vm_area_struct *remove = NULL;
- struct vm_area_struct *remove2 = NULL;
+ struct vm_area_struct *vma;
struct vma_prepare vp;
- struct vm_area_struct *adjust = NULL;
+ struct vm_area_struct *adjust;
long adj_start;
- bool merge_target;
/*
* If modifying an existing VMA and we don't remove vmg->middle, then we
* shrink the adjacent VMA.
*/
if (vmg->__adjust_middle_start) {
+ vma = vmg->target;
adjust = vmg->middle;
/* The POSITIVE value by which we offset vmg->middle->vm_start. */
adj_start = vmg->end - vmg->middle->vm_start;
- merge_target = true;
+
+ /* Note: vma iterator must be pointing to 'start'. */
+ vma_iter_config(vmg->vmi, vmg->start, vmg->end);
} else if (vmg->__adjust_next_start) {
+ /*
+ * In this case alone, the VMA we manipulate is vmg->middle, but
+ * we ultimately return vmg->next.
+ */
+ vma = vmg->middle;
adjust = vmg->next;
/* The NEGATIVE value by which we offset vmg->next->vm_start. */
adj_start = -(vmg->middle->vm_end - vmg->end);
- /*
- * In all cases but this - merge right, shrink next - we write
- * vmg->target to the maple tree and return this as the merged VMA.
- */
- merge_target = false;
+
+ vma_iter_config(vmg->vmi, vmg->next->vm_start + adj_start,
+ vmg->next->vm_end);
} else {
+ vma = vmg->target;
adjust = NULL;
adj_start = 0;
- merge_target = true;
- }
-
- if (vmg->__remove_middle)
- remove = vmg->middle;
- if (vmg->__remove_next)
- remove2 = vmg->next;
-
- init_multi_vma_prep(&vp, vmg->target, adjust, remove, remove2);
- VM_WARN_ON(vp.anon_vma && adjust && adjust->anon_vma &&
- vp.anon_vma != adjust->anon_vma);
-
- if (merge_target) {
- /* Note: vma iterator must be pointing to 'start'. */
+ /* Note: vma iterator must be pointing to 'start'. */
vma_iter_config(vmg->vmi, vmg->start, vmg->end);
- } else {
- vma_iter_config(vmg->vmi, adjust->vm_start + adj_start,
- adjust->vm_end);
}
- if (vma_iter_prealloc(vmg->vmi, vmg->target))
+ init_multi_vma_prep(&vp, vma, vmg);
+
+ if (vma_iter_prealloc(vmg->vmi, vma))
return NULL;
vma_prepare(&vp);
- vma_adjust_trans_huge(vmg->target, vmg->start, vmg->end, adj_start);
- vma_set_range(vmg->target, vmg->start, vmg->end, vmg->pgoff);
-
- if (merge_target)
- vma_iter_store(vmg->vmi, vmg->target);
+ vma_adjust_trans_huge(vma, vmg->start, vmg->end, adj_start);
+ vma_set_range(vma, vmg->start, vmg->end, vmg->pgoff);
if (adj_start) {
adjust->vm_start += adj_start;
adjust->vm_pgoff += PHYS_PFN(adj_start);
-
- if (!merge_target)
- vma_iter_store(vmg->vmi, adjust);
}
- vma_complete(&vp, vmg->vmi, vmg->target->vm_mm);
+ vma_iter_store(vmg->vmi, vmg->target);
+
+ vma_complete(&vp, vmg->vmi, vma->vm_mm);
- return merge_target ? vmg->target : vmg->next;
+ return vmg->target;
}
/* We can only remove VMAs when merging if they do not have a close hook. */
@@ -833,11 +836,15 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
/* No matter what happens, we will be adjusting middle. */
vma_start_write(middle);
- if (merge_left)
- vma_start_write(prev);
-
- if (merge_right)
+ if (merge_right) {
vma_start_write(next);
+ vmg->target = next;
+ }
+
+ if (merge_left) {
+ vma_start_write(prev);
+ vmg->target = prev;
+ }
if (merge_both) {
/*
@@ -847,7 +854,6 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
* extend delete delete
*/
- vmg->target = prev;
vmg->start = prev->vm_start;
vmg->end = next->vm_end;
vmg->pgoff = prev->vm_pgoff;
@@ -868,7 +874,6 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
* extend shrink/delete
*/
- vmg->target = prev;
vmg->start = prev->vm_start;
vmg->pgoff = prev->vm_pgoff;
@@ -892,7 +897,6 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
VM_WARN_ON_VMG(vmg->start > middle->vm_start && prev && middle != prev, vmg);
if (vmg->__remove_middle) {
- vmg->target = next;
vmg->end = next->vm_end;
vmg->pgoff = next->vm_pgoff - pglen;
} else {
@@ -903,7 +907,6 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
* merged VMA is NOT vmg->target, but rather vmg->next.
*/
vmg->__adjust_next_start = true;
- vmg->target = middle;
vmg->start = middle->vm_start;
vmg->end = start;
vmg->pgoff = middle->vm_pgoff;
diff --git a/mm/vma.h b/mm/vma.h
index e18487797fa4..e55e68abfbe3 100644
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -82,11 +82,7 @@ struct vma_merge_struct {
struct vm_area_struct *prev;
struct vm_area_struct *middle;
struct vm_area_struct *next;
- /*
- * This is the VMA we ultimately target to become the merged VMA, except
- * for the one exception of merge right, shrink next (for details of
- * this scenario see vma_merge_existing_range()).
- */
+ /* This is the VMA we ultimately target to become the merged VMA. */
struct vm_area_struct *target;
/*
* Initially, the start, end, pgoff fields are provided by the caller
--
2.48.1
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH v3 5/5] mm: completely abstract unnecessary adj_start calculation
2025-01-31 12:31 [PATCH v3 0/5] mm: further simplify VMA merge operation Lorenzo Stoakes
` (3 preceding siblings ...)
2025-01-31 12:31 ` [PATCH v3 4/5] mm: make vmg->target consistent and further simplify commit_merge() Lorenzo Stoakes
@ 2025-01-31 12:31 ` Lorenzo Stoakes
4 siblings, 0 replies; 6+ messages in thread
From: Lorenzo Stoakes @ 2025-01-31 12:31 UTC (permalink / raw)
To: Andrew Morton
Cc: Liam R . Howlett, Vlastimil Babka, Jann Horn, linux-mm, linux-kernel
The adj_start calculation has been a constant source of confusion in the
VMA merge code.
There are two cases to consider, one where we adjust the start of the
vmg->middle VMA (i.e. the vmg->__adjust_middle_start merge flag is set), in
which case adj_start is calculated as:
(1) adj_start = vmg->end - vmg->middle->vm_start
And the case where we adjust the start of the vmg->next VMA (i.e. the
vmg->__adjust_next_start merge flag is set), in which case adj_start is
calculated as:
(2) adj_start = -(vmg->middle->vm_end - vmg->end)
We apply (1) thusly:
vmg->middle->vm_start =
vmg->middle->vm_start + vmg->end - vmg->middle->vm_start
Which simplifies to:
vmg->middle->vm_start = vmg->end
Similarly, we apply (2) as:
vmg->next->vm_start =
vmg->next->vm_start + -(vmg->middle->vm_end - vmg->end)
Noting that for these VMAs to be mergeable vmg->middle->vm_end ==
vmg->next->vm_start and so this simplifies to:
vmg->next->vm_start =
vmg->next->vm_start + -(vmg->next->vm_start - vmg->end)
Which simplifies to:
vmg->next->vm_start = vmg->end
Therefore in each case, we simply need to adjust the start of the VMA to
vmg->end (!) and can do away with this adj_start calculation. The only
caveat is that we must ensure we update the vm_pgoff field correctly.
We therefore abstract this entire calculation to a new function
vmg_adjust_set_range() which performs this calculation and sets the
adjusted VMA's new range using the general vma_set_range() function.
We also must update vma_adjust_trans_huge() which expects the
now-abstracted adj_start parameter. It turns out this is wholly
unnecessary.
In vma_adjust_trans_huge() the relevant code is:
if (adjust_next > 0) {
struct vm_area_struct *next = find_vma(vma->vm_mm, vma->vm_end);
unsigned long nstart = next->vm_start;
nstart += adjust_next;
split_huge_pmd_if_needed(next, nstart);
}
The only case where this is relevant is when vmg->__adjust_middle_start is
specified (in which case adj_next would have been positive), i.e. the one
in which the vma specified is vmg->prev and this the sought 'next' VMA
would be vmg->middle.
We can therefore eliminate the find_vma() invocation altogether and simply
provide the vmg->middle VMA in this instance, or NULL otherwise.
Again we have an adj_next offset calculation:
next->vm_start + vmg->end - vmg->middle->vm_start
Where next == vmg->middle this simplifies to vmg->end as previously
demonstrated.
Therefore nstart is equal to vmg->end, which is already passed to
vma_adjust_trans_huge() via the 'end' parameter and so this code (rather
delightfully) simplifies to:
if (next)
split_huge_pmd_if_needed(next, end);
With these changes in place, it becomes silly for commit_merge() to return
vmg->target, as it is always the same and threaded through vmg, so we
finally change commit_merge() to return an error value once again.
This patch has no change in functional behaviour.
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
---
include/linux/huge_mm.h | 4 +-
mm/huge_memory.c | 19 ++----
mm/vma.c | 99 +++++++++++++++-----------------
tools/testing/vma/vma_internal.h | 4 +-
4 files changed, 57 insertions(+), 69 deletions(-)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 93e509b6c00e..e1bea54820ff 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -404,7 +404,7 @@ int madvise_collapse(struct vm_area_struct *vma,
struct vm_area_struct **prev,
unsigned long start, unsigned long end);
void vma_adjust_trans_huge(struct vm_area_struct *vma, unsigned long start,
- unsigned long end, long adjust_next);
+ unsigned long end, struct vm_area_struct *next);
spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma);
spinlock_t *__pud_trans_huge_lock(pud_t *pud, struct vm_area_struct *vma);
@@ -571,7 +571,7 @@ static inline int madvise_collapse(struct vm_area_struct *vma,
static inline void vma_adjust_trans_huge(struct vm_area_struct *vma,
unsigned long start,
unsigned long end,
- long adjust_next)
+ struct vm_area_struct *next)
{
}
static inline int is_swap_pmd(pmd_t pmd)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8d21218dc740..de72713b1c45 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3017,9 +3017,9 @@ static inline void split_huge_pmd_if_needed(struct vm_area_struct *vma, unsigned
}
void vma_adjust_trans_huge(struct vm_area_struct *vma,
- unsigned long start,
- unsigned long end,
- long adjust_next)
+ unsigned long start,
+ unsigned long end,
+ struct vm_area_struct *next)
{
/* Check if we need to split start first. */
split_huge_pmd_if_needed(vma, start);
@@ -3027,16 +3027,9 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma,
/* Check if we need to split end next. */
split_huge_pmd_if_needed(vma, end);
- /*
- * If we're also updating the next vma vm_start,
- * check if we need to split it.
- */
- if (adjust_next > 0) {
- struct vm_area_struct *next = find_vma(vma->vm_mm, vma->vm_end);
- unsigned long nstart = next->vm_start;
- nstart += adjust_next;
- split_huge_pmd_if_needed(next, nstart);
- }
+ /* If we're incrementing next->vm_start, we might need to split it. */
+ if (next)
+ split_huge_pmd_if_needed(next, end);
}
static void unmap_folio(struct folio *folio)
diff --git a/mm/vma.c b/mm/vma.c
index 75bbe82b2e65..39146c19f316 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -513,7 +513,7 @@ __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
init_vma_prep(&vp, vma);
vp.insert = new;
vma_prepare(&vp);
- vma_adjust_trans_huge(vma, vma->vm_start, addr, 0);
+ vma_adjust_trans_huge(vma, vma->vm_start, addr, NULL);
if (new_below) {
vma->vm_start = addr;
@@ -644,46 +644,44 @@ void validate_mm(struct mm_struct *mm)
#endif /* CONFIG_DEBUG_VM_MAPLE_TREE */
/*
- * Actually perform the VMA merge operation.
- *
- * On success, returns the merged VMA. Otherwise returns NULL.
+ * Based on the vmg flag indicating whether we need to adjust the vm_start field
+ * for the middle or next VMA, we calculate what the range of the newly adjusted
+ * VMA ought to be, and set the VMA's range accordingly.
*/
-static struct vm_area_struct *commit_merge(struct vma_merge_struct *vmg)
+static void vmg_adjust_set_range(struct vma_merge_struct *vmg)
{
- struct vm_area_struct *vma;
- struct vma_prepare vp;
struct vm_area_struct *adjust;
- long adj_start;
+ pgoff_t pgoff;
- /*
- * If modifying an existing VMA and we don't remove vmg->middle, then we
- * shrink the adjacent VMA.
- */
if (vmg->__adjust_middle_start) {
- vma = vmg->target;
adjust = vmg->middle;
- /* The POSITIVE value by which we offset vmg->middle->vm_start. */
- adj_start = vmg->end - vmg->middle->vm_start;
-
- /* Note: vma iterator must be pointing to 'start'. */
- vma_iter_config(vmg->vmi, vmg->start, vmg->end);
+ pgoff = adjust->vm_pgoff + PHYS_PFN(vmg->end - adjust->vm_start);
} else if (vmg->__adjust_next_start) {
- /*
- * In this case alone, the VMA we manipulate is vmg->middle, but
- * we ultimately return vmg->next.
- */
- vma = vmg->middle;
adjust = vmg->next;
- /* The NEGATIVE value by which we offset vmg->next->vm_start. */
- adj_start = -(vmg->middle->vm_end - vmg->end);
+ pgoff = adjust->vm_pgoff - PHYS_PFN(adjust->vm_start - vmg->end);
+ } else {
+ return;
+ }
+
+ vma_set_range(adjust, vmg->end, adjust->vm_end, pgoff);
+}
+
+/*
+ * Actually perform the VMA merge operation.
+ *
+ * Returns 0 on success, or an error value on failure.
+ */
+static int commit_merge(struct vma_merge_struct *vmg)
+{
+ struct vm_area_struct *vma;
+ struct vma_prepare vp;
- vma_iter_config(vmg->vmi, vmg->next->vm_start + adj_start,
- vmg->next->vm_end);
+ if (vmg->__adjust_next_start) {
+ /* We manipulate middle and adjust next, which is the target. */
+ vma = vmg->middle;
+ vma_iter_config(vmg->vmi, vmg->end, vmg->next->vm_end);
} else {
vma = vmg->target;
- adjust = NULL;
- adj_start = 0;
-
/* Note: vma iterator must be pointing to 'start'. */
vma_iter_config(vmg->vmi, vmg->start, vmg->end);
}
@@ -691,22 +689,22 @@ static struct vm_area_struct *commit_merge(struct vma_merge_struct *vmg)
init_multi_vma_prep(&vp, vma, vmg);
if (vma_iter_prealloc(vmg->vmi, vma))
- return NULL;
+ return -ENOMEM;
vma_prepare(&vp);
- vma_adjust_trans_huge(vma, vmg->start, vmg->end, adj_start);
+ /*
+ * THP pages may need to do additional splits if we increase
+ * middle->vm_start.
+ */
+ vma_adjust_trans_huge(vma, vmg->start, vmg->end,
+ vmg->__adjust_middle_start ? vmg->middle : NULL);
vma_set_range(vma, vmg->start, vmg->end, vmg->pgoff);
-
- if (adj_start) {
- adjust->vm_start += adj_start;
- adjust->vm_pgoff += PHYS_PFN(adj_start);
- }
-
+ vmg_adjust_set_range(vmg);
vma_iter_store(vmg->vmi, vmg->target);
vma_complete(&vp, vmg->vmi, vma->vm_mm);
- return vmg->target;
+ return 0;
}
/* We can only remove VMAs when merging if they do not have a close hook. */
@@ -749,7 +747,7 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
{
struct vm_area_struct *middle = vmg->middle;
struct vm_area_struct *prev = vmg->prev;
- struct vm_area_struct *next, *res;
+ struct vm_area_struct *next;
struct vm_area_struct *anon_dup = NULL;
unsigned long start = vmg->start;
unsigned long end = vmg->end;
@@ -900,12 +898,7 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
vmg->end = next->vm_end;
vmg->pgoff = next->vm_pgoff - pglen;
} else {
- /*
- * We shrink middle and expand next.
- *
- * IMPORTANT: This is the ONLY case where the final
- * merged VMA is NOT vmg->target, but rather vmg->next.
- */
+ /* We shrink middle and expand next. */
vmg->__adjust_next_start = true;
vmg->start = middle->vm_start;
vmg->end = start;
@@ -918,8 +911,10 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
if (err)
goto abort;
- res = commit_merge(vmg);
- if (!res) {
+ err = commit_merge(vmg);
+ if (err) {
+ VM_WARN_ON(err != -ENOMEM);
+
if (anon_dup)
unlink_anon_vmas(anon_dup);
@@ -927,9 +922,9 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
return NULL;
}
- khugepaged_enter_vma(res, vmg->flags);
+ khugepaged_enter_vma(vmg->target, vmg->flags);
vmg->state = VMA_MERGE_SUCCESS;
- return res;
+ return vmg->target;
abort:
vma_iter_set(vmg->vmi, start);
@@ -1092,7 +1087,7 @@ int vma_expand(struct vma_merge_struct *vmg)
if (remove_next)
vmg->__remove_next = true;
- if (!commit_merge(vmg))
+ if (commit_merge(vmg))
goto nomem;
return 0;
@@ -1132,7 +1127,7 @@ int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
init_vma_prep(&vp, vma);
vma_prepare(&vp);
- vma_adjust_trans_huge(vma, start, end, 0);
+ vma_adjust_trans_huge(vma, start, end, NULL);
vma_iter_clear(vmi);
vma_set_range(vma, start, end, pgoff);
diff --git a/tools/testing/vma/vma_internal.h b/tools/testing/vma/vma_internal.h
index 1eae23039854..bb273927af0f 100644
--- a/tools/testing/vma/vma_internal.h
+++ b/tools/testing/vma/vma_internal.h
@@ -796,12 +796,12 @@ static inline void vma_start_write(struct vm_area_struct *vma)
static inline void vma_adjust_trans_huge(struct vm_area_struct *vma,
unsigned long start,
unsigned long end,
- long adjust_next)
+ struct vm_area_struct *next)
{
(void)vma;
(void)start;
(void)end;
- (void)adjust_next;
+ (void)next;
}
static inline void vma_iter_free(struct vma_iterator *vmi)
--
2.48.1
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2025-01-31 12:33 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2025-01-31 12:31 [PATCH v3 0/5] mm: further simplify VMA merge operation Lorenzo Stoakes
2025-01-31 12:31 ` [PATCH v3 1/5] mm: simplify vma merge structure and expand comments Lorenzo Stoakes
2025-01-31 12:31 ` [PATCH v3 2/5] mm: further refactor commit_merge() Lorenzo Stoakes
2025-01-31 12:31 ` [PATCH v3 3/5] mm: eliminate adj_start parameter from commit_merge() Lorenzo Stoakes
2025-01-31 12:31 ` [PATCH v3 4/5] mm: make vmg->target consistent and further simplify commit_merge() Lorenzo Stoakes
2025-01-31 12:31 ` [PATCH v3 5/5] mm: completely abstract unnecessary adj_start calculation Lorenzo Stoakes
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