[PATCH 1/2] mm: add vma_has_locality()

[PATCH 1/2] mm: add vma_has_locality()

[Yuanchu Xie]

From: Yu Zhao <yuzhao@google.com>

Currently in vm_flags in vm_area_struct, both VM_SEQ_READ and
VM_RAND_READ indicate a lack of locality in accesses to the vma. Some
places that check for locality are missing one of them. We add
vma_has_locality to replace the existing locality checks for clarity.

Signed-off-by: Yu Zhao <yuzhao@google.com>
Signed-off-by: Yuanchu Xie <yuanchu@google.com>
---
 include/linux/mm_inline.h |  8 ++++++++
 mm/memory.c               |  7 +++----
 mm/rmap.c                 | 42 +++++++++++++++++----------------------
 mm/vmscan.c               |  5 ++++-
 4 files changed, 33 insertions(+), 29 deletions(-)

diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index e8ed225d8f7c..80c0f6901ead 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -578,4 +578,12 @@ pte_install_uffd_wp_if_needed(struct vm_area_struct *vma, unsigned long addr,
 #endif
 }
 
+static inline bool vma_has_locality(struct vm_area_struct *vma)
+{
+	if (vma->vm_flags & (VM_SEQ_READ | VM_RAND_READ))
+		return false;
+
+	return true;
+}
+
 #endif
diff --git a/mm/memory.c b/mm/memory.c
index 4000e9f017e0..a3f60e53f348 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1402,8 +1402,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
 						force_flush = 1;
 					}
 				}
-				if (pte_young(ptent) &&
-				    likely(!(vma->vm_flags & VM_SEQ_READ)))
+				if (pte_young(ptent) && likely(vma_has_locality(vma)))
 					mark_page_accessed(page);
 			}
 			rss[mm_counter(page)]--;
@@ -5148,8 +5147,8 @@ static inline void mm_account_fault(struct pt_regs *regs,
 #ifdef CONFIG_LRU_GEN
 static void lru_gen_enter_fault(struct vm_area_struct *vma)
 {
-	/* the LRU algorithm doesn't apply to sequential or random reads */
-	current->in_lru_fault = !(vma->vm_flags & (VM_SEQ_READ | VM_RAND_READ));
+	/* the LRU algorithm only applies to accesses with locality */
+	current->in_lru_fault = vma_has_locality(vma);
 }
 
 static void lru_gen_exit_fault(void)
diff --git a/mm/rmap.c b/mm/rmap.c
index 32e48b1c5847..a2e83fea6fed 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -823,25 +823,14 @@ static bool folio_referenced_one(struct folio *folio,
 		}
 
 		if (pvmw.pte) {
-			if (lru_gen_enabled() && pte_young(*pvmw.pte) &&
-			    !(vma->vm_flags & (VM_SEQ_READ | VM_RAND_READ))) {
+			if (lru_gen_enabled() && pte_young(*pvmw.pte)) {
 				lru_gen_look_around(&pvmw);
 				referenced++;
 			}
 
 			if (ptep_clear_flush_young_notify(vma, address,
-						pvmw.pte)) {
-				/*
-				 * Don't treat a reference through
-				 * a sequentially read mapping as such.
-				 * If the folio has been used in another mapping,
-				 * we will catch it; if this other mapping is
-				 * already gone, the unmap path will have set
-				 * the referenced flag or activated the folio.
-				 */
-				if (likely(!(vma->vm_flags & VM_SEQ_READ)))
-					referenced++;
-			}
+						pvmw.pte))
+				referenced++;
 		} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
 			if (pmdp_clear_flush_young_notify(vma, address,
 						pvmw.pmd))
@@ -875,7 +864,20 @@ static bool invalid_folio_referenced_vma(struct vm_area_struct *vma, void *arg)
 	struct folio_referenced_arg *pra = arg;
 	struct mem_cgroup *memcg = pra->memcg;
 
-	if (!mm_match_cgroup(vma->vm_mm, memcg))
+	/*
+	 * Ignore references from this mapping if it has no locality. If the
+	 * folio has been used in another mapping, we will catch it; if this
+	 * other mapping is already gone, the unmap path will have set the
+	 * referenced flag or activated the folio in zap_pte_range().
+	 */
+	if (!vma_has_locality(vma))
+		return true;
+
+	/*
+	 * If we are reclaiming on behalf of a cgroup, skip counting on behalf
+	 * of references from different cgroups
+	 */
+	if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
 		return true;
 
 	return false;
@@ -906,6 +908,7 @@ int folio_referenced(struct folio *folio, int is_locked,
 		.arg = (void *)&pra,
 		.anon_lock = folio_lock_anon_vma_read,
 		.try_lock = true,
+		.invalid_vma = invalid_folio_referenced_vma,
 	};
 
 	*vm_flags = 0;
@@ -921,15 +924,6 @@ int folio_referenced(struct folio *folio, int is_locked,
 			return 1;
 	}
 
-	/*
-	 * If we are reclaiming on behalf of a cgroup, skip
-	 * counting on behalf of references from different
-	 * cgroups
-	 */
-	if (memcg) {
-		rwc.invalid_vma = invalid_folio_referenced_vma;
-	}
-
 	rmap_walk(folio, &rwc);
 	*vm_flags = pra.vm_flags;
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index e83d2a74e942..5cf39f314876 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3782,7 +3782,10 @@ static int should_skip_vma(unsigned long start, unsigned long end, struct mm_wal
 	if (is_vm_hugetlb_page(vma))
 		return true;
 
-	if (vma->vm_flags & (VM_LOCKED | VM_SPECIAL | VM_SEQ_READ | VM_RAND_READ))
+	if (!vma_has_locality(vma))
+		return true;
+
+	if (vma->vm_flags & (VM_LOCKED | VM_SPECIAL))
 		return true;
 
 	if (vma == get_gate_vma(vma->vm_mm))
-- 
2.39.0.314.g84b9a713c41-goog

[PATCH 2/2] mm: support POSIX_FADV_NOREUSE for generic fadvise handler

[Yuanchu Xie]

From: Yu Zhao <yuzhao@google.com>

POSIX_FADV_NOREUSE allows an application to specify that accesses to
file data does not follow LRU and is used only once. Since 2.6.18 this
is a no-op. We add FMODE_NOREUSE, checked in vma_has_locality to prevent
LRU activation.

Signed-off-by: Yu Zhao <yuzhao@google.com>
Signed-off-by: Yuanchu Xie <yuanchu@google.com>
---
 include/linux/fs.h        | 2 ++
 include/linux/mm_inline.h | 3 +++
 mm/fadvise.c              | 5 ++++-
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 066555ad1bf8..5660ed0edf1a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -166,6 +166,8 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
 /* File supports DIRECT IO */
 #define	FMODE_CAN_ODIRECT	((__force fmode_t)0x400000)
 
+#define	FMODE_NOREUSE		((__force fmode_t)0x800000)
+
 /* File was opened by fanotify and shouldn't generate fanotify events */
 #define FMODE_NONOTIFY		((__force fmode_t)0x4000000)
 
diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index 80c0f6901ead..024f834d952d 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -583,6 +583,9 @@ static inline bool vma_has_locality(struct vm_area_struct *vma)
 	if (vma->vm_flags & (VM_SEQ_READ | VM_RAND_READ))
 		return false;
 
+	if (vma->vm_file && (vma->vm_file->f_mode & FMODE_NOREUSE))
+		return false;
+
 	return true;
 }
 
diff --git a/mm/fadvise.c b/mm/fadvise.c
index bf04fec87f35..fb7c5f43fd2a 100644
--- a/mm/fadvise.c
+++ b/mm/fadvise.c
@@ -80,7 +80,7 @@ int generic_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 	case POSIX_FADV_NORMAL:
 		file->f_ra.ra_pages = bdi->ra_pages;
 		spin_lock(&file->f_lock);
-		file->f_mode &= ~FMODE_RANDOM;
+		file->f_mode &= ~(FMODE_RANDOM | FMODE_NOREUSE);
 		spin_unlock(&file->f_lock);
 		break;
 	case POSIX_FADV_RANDOM:
@@ -107,6 +107,9 @@ int generic_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 		force_page_cache_readahead(mapping, file, start_index, nrpages);
 		break;
 	case POSIX_FADV_NOREUSE:
+		spin_lock(&file->f_lock);
+		file->f_mode |= FMODE_NOREUSE;
+		spin_unlock(&file->f_lock);
 		break;
 	case POSIX_FADV_DONTNEED:
 		__filemap_fdatawrite_range(mapping, offset, endbyte,
-- 
2.39.0.314.g84b9a713c41-goog

Re: [PATCH 1/2] mm: add vma_has_locality()

[Yuanchu Xie]

I forgot to add the Ack from Johannes earlier[1]

[1] https://lore.kernel.org/all/Y36PF972kOK3ADvx@cmpxchg.org/


Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Re: [PATCH 1/2] mm: add vma_has_locality()

[Andrew Morton]

On Wed, 21 Dec 2022 22:13:40 -0800 Yuanchu Xie <yuanchu@google.com> wrote:

> From: Yu Zhao <yuzhao@google.com>
> 
> Currently in vm_flags in vm_area_struct, both VM_SEQ_READ and
> VM_RAND_READ indicate a lack of locality in accesses to the vma. Some
> places that check for locality are missing one of them. We add
> vma_has_locality to replace the existing locality checks for clarity.

I'm all confused.  Surely VM_SEQ_READ implies locality and VM_RAND_READ
indicates no-locality?

Re: [PATCH 1/2] mm: add vma_has_locality()

[Yu Zhao]

On Thu, Dec 22, 2022 at 11:49 AM Andrew Morton
<akpm@linux-foundation.org> wrote:
>
> On Wed, 21 Dec 2022 22:13:40 -0800 Yuanchu Xie <yuanchu@google.com> wrote:
>
> > From: Yu Zhao <yuzhao@google.com>

This works; suggested-by probably works even better, since I didn't do
the follow-up work.

> > Currently in vm_flags in vm_area_struct, both VM_SEQ_READ and
> > VM_RAND_READ indicate a lack of locality in accesses to the vma. Some
> > places that check for locality are missing one of them. We add
> > vma_has_locality to replace the existing locality checks for clarity.
>
> I'm all confused.  Surely VM_SEQ_READ implies locality and VM_RAND_READ
> indicates no-locality?

Spatially, yes. But we focus more on the temporal criteria here, i.e.,
the reuse of an area within a relatively small duration. Both the
active/inactive LRU and MGLRU rely on this.

VM_SEQ_READ, while being a special case of spatial locality, fails the
temporal criteria. VM_RAND_READ fails both criterias, obviously.

Once an area passes the temporal criteria, MGLRU additionally exploits
spatial locality by lru_gen_look_around(), which is also touched in
this patch. This part is good to know but not really relevant here.

Re: [PATCH 1/2] mm: add vma_has_locality()

[Yu Zhao]

On Wed, Dec 21, 2022 at 11:13 PM Yuanchu Xie <yuanchu@google.com> wrote:
>
> From: Yu Zhao <yuzhao@google.com>
>
> Currently in vm_flags in vm_area_struct, both VM_SEQ_READ and
> VM_RAND_READ indicate a lack of locality in accesses to the vma. Some
> places that check for locality are missing one of them. We add
> vma_has_locality to replace the existing locality checks for clarity.

Need benchmark results. A simple fio test will do; doesn't need to be
the curl one.

> +       /*
> +        * If we are reclaiming on behalf of a cgroup, skip counting on behalf
> +        * of references from different cgroups

Nit: add a period at the end.

> @@ -906,6 +908,7 @@ int folio_referenced(struct folio *folio, int is_locked,
>                 .arg = (void *)&pra,
>                 .anon_lock = folio_lock_anon_vma_read,
>                 .try_lock = true,
> +               .invalid_vma = invalid_folio_referenced_vma,

Nice. (What I suggested isn't as clean:
https://lore.kernel.org/all/Y31s%2FK8T85jh05wH@google.com/)

Re: [PATCH 1/2] mm: add vma_has_locality()

[Andrew Morton]

On Thu, 22 Dec 2022 12:44:35 -0700 Yu Zhao <yuzhao@google.com> wrote:

> On Thu, Dec 22, 2022 at 11:49 AM Andrew Morton
> <akpm@linux-foundation.org> wrote:
> >
> > On Wed, 21 Dec 2022 22:13:40 -0800 Yuanchu Xie <yuanchu@google.com> wrote:
> >
> > > From: Yu Zhao <yuzhao@google.com>
> 
> This works; suggested-by probably works even better, since I didn't do
> the follow-up work.
> 
> > > Currently in vm_flags in vm_area_struct, both VM_SEQ_READ and
> > > VM_RAND_READ indicate a lack of locality in accesses to the vma. Some
> > > places that check for locality are missing one of them. We add
> > > vma_has_locality to replace the existing locality checks for clarity.
> >
> > I'm all confused.  Surely VM_SEQ_READ implies locality and VM_RAND_READ
> > indicates no-locality?
> 
> Spatially, yes. But we focus more on the temporal criteria here, i.e.,
> the reuse of an area within a relatively small duration. Both the
> active/inactive LRU and MGLRU rely on this.

Oh.  Why didn't it say that ;)

How about s/locality/recency/g?

Re: [PATCH 2/2] mm: support POSIX_FADV_NOREUSE for generic fadvise handler

[Yu Zhao]

On Wed, Dec 21, 2022 at 11:13 PM Yuanchu Xie <yuanchu@google.com> wrote:

Thanks for following up on this.

> POSIX_FADV_NOREUSE allows an application to specify that accesses to
> file data does not follow LRU and is used only once. Since 2.6.18 this
> is a no-op. We add FMODE_NOREUSE, checked in vma_has_locality to prevent
> LRU activation.

This needs to include what you plan to write on the man page.

A few questions to answer:
1. Does this flag work with accesses via FDs?
2. If there is a random or sequential file VMA, should the user choose
this flag or the VMA flag or both? Consider a) how those flags affect
readahead; b) their scopes, i.e., per VMA or per file.

Please also follow up with Jens to add this flag to fio.

Micheal reported that SVT-AV1 regressed with MGLRU, which is the only
real one [1]. The following not only fixes the regression but also
improves the baseline. Please follow up on that as well.

--- a/Source/App/EncApp/EbAppMain.c
+++ b/Source/App/EncApp/EbAppMain.c
@@ -115,6 +115,7 @@ void init_memory_file_map(EbConfig* config) {
             fseeko(config->input_file, curr_loc, SEEK_SET); // seek
back to that location
 #ifndef _WIN32
             config->mmap.fd = fileno(config->input_file);
+            posix_fadvise(config->mmap.fd, 0, 0, POSIX_FADV_NOREUSE);
 #endif
         }
         config->mmap.file_frame_it = 0;

[1] https://openbenchmarking.org/result/2209259-PTS-MGLRU8GB57

Re: [PATCH 1/2] mm: add vma_has_locality()

[Yu Zhao]

On Thu, Dec 22, 2022 at 1:29 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Thu, 22 Dec 2022 12:44:35 -0700 Yu Zhao <yuzhao@google.com> wrote:
>
> > On Thu, Dec 22, 2022 at 11:49 AM Andrew Morton
> > <akpm@linux-foundation.org> wrote:
> > >
> > > On Wed, 21 Dec 2022 22:13:40 -0800 Yuanchu Xie <yuanchu@google.com> wrote:
> > >
> > > > From: Yu Zhao <yuzhao@google.com>
> >
> > This works; suggested-by probably works even better, since I didn't do
> > the follow-up work.
> >
> > > > Currently in vm_flags in vm_area_struct, both VM_SEQ_READ and
> > > > VM_RAND_READ indicate a lack of locality in accesses to the vma. Some
> > > > places that check for locality are missing one of them. We add
> > > > vma_has_locality to replace the existing locality checks for clarity.
> > >
> > > I'm all confused.  Surely VM_SEQ_READ implies locality and VM_RAND_READ
> > > indicates no-locality?
> >
> > Spatially, yes. But we focus more on the temporal criteria here, i.e.,
> > the reuse of an area within a relatively small duration. Both the
> > active/inactive LRU and MGLRU rely on this.
>
> Oh.  Why didn't it say that ;)
>
> How about s/locality/recency/g?

Thanks. I've done this, and posted the v2 which includes much better
commit messages.