* [RFC] Trylock the mmap_lock in vmf_anon_prepare()
@ 2024-04-15 15:24 Matthew Wilcox
2024-04-15 16:14 ` Suren Baghdasaryan
2024-04-15 16:45 ` Jann Horn
0 siblings, 2 replies; 5+ messages in thread
From: Matthew Wilcox @ 2024-04-15 15:24 UTC (permalink / raw)
To: linux-mm; +Cc: Suren Baghdasaryan
It seems a shame to fallback if the mmap_lock is readily available.
It doesn't blow up immediately in my testing ... thoughts?
From 70833af858ce41a80b5f0669648ee9f59b149a03 Mon Sep 17 00:00:00 2001
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Date: Mon, 15 Apr 2024 11:13:41 -0400
Subject: [PATCH] mm: Optimise vmf_anon_prepare() for VMAs without an anon_vma
If the mmap_lock can be taken for read, there's no reason not to take
it so that we can call __anon_vma_prepare().
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
mm/memory.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index b9c23393fa9b..7075fb7f74da 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3219,11 +3219,15 @@ vm_fault_t vmf_anon_prepare(struct vm_fault *vmf)
if (likely(vma->anon_vma))
return 0;
if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
- vma_end_read(vma);
- return VM_FAULT_RETRY;
+ if (!mmap_read_trylock(vma->vm_mm)) {
+ vma_end_read(vma);
+ return VM_FAULT_RETRY;
+ }
}
if (__anon_vma_prepare(vma))
return VM_FAULT_OOM;
+ if (vmf->flags & FAULT_FLAG_VMA_LOCK)
+ mmap_read_unlock(vma->vm_mm);
return 0;
}
--
2.43.0
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [RFC] Trylock the mmap_lock in vmf_anon_prepare()
2024-04-15 15:24 [RFC] Trylock the mmap_lock in vmf_anon_prepare() Matthew Wilcox
@ 2024-04-15 16:14 ` Suren Baghdasaryan
2024-04-15 18:18 ` Matthew Wilcox
2024-04-15 16:45 ` Jann Horn
1 sibling, 1 reply; 5+ messages in thread
From: Suren Baghdasaryan @ 2024-04-15 16:14 UTC (permalink / raw)
To: Matthew Wilcox; +Cc: linux-mm
On Mon, Apr 15, 2024 at 8:24 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> It seems a shame to fallback if the mmap_lock is readily available.
> It doesn't blow up immediately in my testing ... thoughts?
I can't think of anything that would break...
>
> From 70833af858ce41a80b5f0669648ee9f59b149a03 Mon Sep 17 00:00:00 2001
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> Date: Mon, 15 Apr 2024 11:13:41 -0400
> Subject: [PATCH] mm: Optimise vmf_anon_prepare() for VMAs without an anon_vma
>
> If the mmap_lock can be taken for read, there's no reason not to take
> it so that we can call __anon_vma_prepare().
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
> mm/memory.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index b9c23393fa9b..7075fb7f74da 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3219,11 +3219,15 @@ vm_fault_t vmf_anon_prepare(struct vm_fault *vmf)
> if (likely(vma->anon_vma))
> return 0;
> if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
> - vma_end_read(vma);
> - return VM_FAULT_RETRY;
> + if (!mmap_read_trylock(vma->vm_mm)) {
> + vma_end_read(vma);
> + return VM_FAULT_RETRY;
> + }
> }
> if (__anon_vma_prepare(vma))
> return VM_FAULT_OOM;
You should drop mmap_lock when returning VM_FAULT_OOM as well.
> + if (vmf->flags & FAULT_FLAG_VMA_LOCK)
> + mmap_read_unlock(vma->vm_mm);
> return 0;
> }
>
> --
> 2.43.0
>
>
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [RFC] Trylock the mmap_lock in vmf_anon_prepare()
2024-04-15 16:14 ` Suren Baghdasaryan
@ 2024-04-15 18:18 ` Matthew Wilcox
2024-04-15 20:59 ` Suren Baghdasaryan
0 siblings, 1 reply; 5+ messages in thread
From: Matthew Wilcox @ 2024-04-15 18:18 UTC (permalink / raw)
To: Suren Baghdasaryan; +Cc: linux-mm
On Mon, Apr 15, 2024 at 09:14:10AM -0700, Suren Baghdasaryan wrote:
> > if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
> > - vma_end_read(vma);
> > - return VM_FAULT_RETRY;
> > + if (!mmap_read_trylock(vma->vm_mm)) {
> > + vma_end_read(vma);
> > + return VM_FAULT_RETRY;
> > + }
> > }
> > if (__anon_vma_prepare(vma))
> > return VM_FAULT_OOM;
>
> You should drop mmap_lock when returning VM_FAULT_OOM as well.
>
> > + if (vmf->flags & FAULT_FLAG_VMA_LOCK)
> > + mmap_read_unlock(vma->vm_mm);
> > return 0;
> > }
Thanks. Fixed and pushed to
git://git.infradead.org/users/willy/pagecache.git vma-lock
+++ b/mm/memory.c
@@ -3224,16 +3224,21 @@ static inline vm_fault_t vmf_can_call_fault(const struct vm_fault *vmf)
vm_fault_t vmf_anon_prepare(struct vm_fault *vmf)
{
struct vm_area_struct *vma = vmf->vma;
+ vm_fault_t ret = 0;
if (likely(vma->anon_vma))
return 0;
if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
- vma_end_read(vma);
- return VM_FAULT_RETRY;
+ if (!mmap_read_trylock(vma->vm_mm)) {
+ vma_end_read(vma);
+ return VM_FAULT_RETRY;
+ }
}
if (__anon_vma_prepare(vma))
- return VM_FAULT_OOM;
- return 0;
+ ret = VM_FAULT_OOM;
+ if (vmf->flags & FAULT_FLAG_VMA_LOCK)
+ mmap_read_unlock(vma->vm_mm);
+ return ret;
}
/*
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [RFC] Trylock the mmap_lock in vmf_anon_prepare()
2024-04-15 18:18 ` Matthew Wilcox
@ 2024-04-15 20:59 ` Suren Baghdasaryan
0 siblings, 0 replies; 5+ messages in thread
From: Suren Baghdasaryan @ 2024-04-15 20:59 UTC (permalink / raw)
To: Matthew Wilcox; +Cc: linux-mm
On Mon, Apr 15, 2024 at 11:18 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Mon, Apr 15, 2024 at 09:14:10AM -0700, Suren Baghdasaryan wrote:
> > > if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
> > > - vma_end_read(vma);
> > > - return VM_FAULT_RETRY;
> > > + if (!mmap_read_trylock(vma->vm_mm)) {
> > > + vma_end_read(vma);
> > > + return VM_FAULT_RETRY;
> > > + }
> > > }
> > > if (__anon_vma_prepare(vma))
> > > return VM_FAULT_OOM;
> >
> > You should drop mmap_lock when returning VM_FAULT_OOM as well.
> >
> > > + if (vmf->flags & FAULT_FLAG_VMA_LOCK)
> > > + mmap_read_unlock(vma->vm_mm);
> > > return 0;
> > > }
>
> Thanks. Fixed and pushed to
> git://git.infradead.org/users/willy/pagecache.git vma-lock
That looks correct now.
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
>
> +++ b/mm/memory.c
> @@ -3224,16 +3224,21 @@ static inline vm_fault_t vmf_can_call_fault(const struct vm_fault *vmf)
> vm_fault_t vmf_anon_prepare(struct vm_fault *vmf)
> {
> struct vm_area_struct *vma = vmf->vma;
> + vm_fault_t ret = 0;
>
> if (likely(vma->anon_vma))
> return 0;
> if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
> - vma_end_read(vma);
> - return VM_FAULT_RETRY;
> + if (!mmap_read_trylock(vma->vm_mm)) {
> + vma_end_read(vma);
> + return VM_FAULT_RETRY;
> + }
> }
> if (__anon_vma_prepare(vma))
> - return VM_FAULT_OOM;
> - return 0;
> + ret = VM_FAULT_OOM;
> + if (vmf->flags & FAULT_FLAG_VMA_LOCK)
> + mmap_read_unlock(vma->vm_mm);
> + return ret;
> }
>
> /*
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [RFC] Trylock the mmap_lock in vmf_anon_prepare()
2024-04-15 15:24 [RFC] Trylock the mmap_lock in vmf_anon_prepare() Matthew Wilcox
2024-04-15 16:14 ` Suren Baghdasaryan
@ 2024-04-15 16:45 ` Jann Horn
1 sibling, 0 replies; 5+ messages in thread
From: Jann Horn @ 2024-04-15 16:45 UTC (permalink / raw)
To: Matthew Wilcox; +Cc: linux-mm, Suren Baghdasaryan
On Mon, Apr 15, 2024 at 5:24 PM Matthew Wilcox <willy@infradead.org> wrote:
> It seems a shame to fallback if the mmap_lock is readily available.
> It doesn't blow up immediately in my testing ... thoughts?
Seems fine to me, since nothing below the trylocked mmap_lock does
vma_start_*().
> >From 70833af858ce41a80b5f0669648ee9f59b149a03 Mon Sep 17 00:00:00 2001
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> Date: Mon, 15 Apr 2024 11:13:41 -0400
> Subject: [PATCH] mm: Optimise vmf_anon_prepare() for VMAs without an anon_vma
>
> If the mmap_lock can be taken for read, there's no reason not to take
> it so that we can call __anon_vma_prepare().
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Jann Horn <jannh@google.com>
> ---
> mm/memory.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index b9c23393fa9b..7075fb7f74da 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3219,11 +3219,15 @@ vm_fault_t vmf_anon_prepare(struct vm_fault *vmf)
> if (likely(vma->anon_vma))
> return 0;
> if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
> - vma_end_read(vma);
> - return VM_FAULT_RETRY;
> + if (!mmap_read_trylock(vma->vm_mm)) {
> + vma_end_read(vma);
> + return VM_FAULT_RETRY;
> + }
> }
> if (__anon_vma_prepare(vma))
> return VM_FAULT_OOM;
> + if (vmf->flags & FAULT_FLAG_VMA_LOCK)
> + mmap_read_unlock(vma->vm_mm);
> return 0;
> }
>
> --
> 2.43.0
^ permalink raw reply [flat|nested] 5+ messages in thread
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2024-04-15 15:24 [RFC] Trylock the mmap_lock in vmf_anon_prepare() Matthew Wilcox
2024-04-15 16:14 ` Suren Baghdasaryan
2024-04-15 18:18 ` Matthew Wilcox
2024-04-15 20:59 ` Suren Baghdasaryan
2024-04-15 16:45 ` Jann Horn
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