[PATCH] mm: dont call mmu_notifier_invalidate_page during munlock

[PATCH] mm: dont call mmu_notifier_invalidate_page during munlock

[Konstantin Khlebnikov]

try_to_munlock() searches other mlocked vmas, it never unmaps pages.
There is no reason for invalidation because ptes are left unchanged.

Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com>
---
 mm/rmap.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 9c3e773..75d9d5c 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1225,7 +1225,7 @@ int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 
 out_unmap:
 	pte_unmap_unlock(pte, ptl);
-	if (ret != SWAP_FAIL)
+	if (ret != SWAP_FAIL && TTU_ACTION(flags) != TTU_MUNLOCK)
 		mmu_notifier_invalidate_page(mm, address);
 out:
 	return ret;

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Re: [PATCH] mm: dont call mmu_notifier_invalidate_page during munlock

[Andrew Morton]

On Wed, 28 May 2014 11:59:55 +0400 Konstantin Khlebnikov <koct9i@gmail.com> wrote:

> try_to_munlock() searches other mlocked vmas, it never unmaps pages.
> There is no reason for invalidation because ptes are left unchanged.
> 
> ...
>
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1225,7 +1225,7 @@ int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
>  
>  out_unmap:
>  	pte_unmap_unlock(pte, ptl);
> -	if (ret != SWAP_FAIL)
> +	if (ret != SWAP_FAIL && TTU_ACTION(flags) != TTU_MUNLOCK)
>  		mmu_notifier_invalidate_page(mm, address);
>  out:
>  	return ret;

The patch itself looks reasonable but there is no such thing as
try_to_munlock().  I rewrote the changelog thusly:

: In its munmap mode, try_to_unmap_one() searches other mlocked vmas, it
: never unmaps pages.  There is no reason for invalidation because ptes are
: left unchanged.

Also, the name try_to_unmap_one() is now pretty inaccurate/incomplete. 
Perhaps if someone is feeling enthusiastic they might think up a better
name for the various try_to_unmap functions and see if we can
appropriately document try_to_unmap_one().

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Re: [PATCH] mm: dont call mmu_notifier_invalidate_page during munlock

[Konstantin Khlebnikov]

On Thu, May 29, 2014 at 3:09 AM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Wed, 28 May 2014 11:59:55 +0400 Konstantin Khlebnikov <koct9i@gmail.com> wrote:
>
>> try_to_munlock() searches other mlocked vmas, it never unmaps pages.
>> There is no reason for invalidation because ptes are left unchanged.
>>
>> ...
>>
>> --- a/mm/rmap.c
>> +++ b/mm/rmap.c
>> @@ -1225,7 +1225,7 @@ int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
>>
>>  out_unmap:
>>       pte_unmap_unlock(pte, ptl);
>> -     if (ret != SWAP_FAIL)
>> +     if (ret != SWAP_FAIL && TTU_ACTION(flags) != TTU_MUNLOCK)
>>               mmu_notifier_invalidate_page(mm, address);
>>  out:
>>       return ret;
>
> The patch itself looks reasonable but there is no such thing as
> try_to_munlock().  I rewrote the changelog thusly:

Wait, what? I do have function with this name in my sources. It calls rmap_walk
with callback try_to_unmap_one and action TTU_MUNLOCK. This is the place
where TTU_MUNLOCK is used, I've mentioned it as entry point of this logic.

>
> : In its munmap mode, try_to_unmap_one() searches other mlocked vmas, it
> : never unmaps pages.  There is no reason for invalidation because ptes are
> : left unchanged.
>
> Also, the name try_to_unmap_one() is now pretty inaccurate/incomplete.
> Perhaps if someone is feeling enthusiastic they might think up a better
> name for the various try_to_unmap functions and see if we can
> appropriately document try_to_unmap_one().

I thought about moving mlock part out of try_to_unmap_one() into
separate function,
but normal unmap needs this part too...
Anyway I want to make try_to_unmap_one() static, this is internal function now.

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Re: [PATCH] mm: dont call mmu_notifier_invalidate_page during munlock

[Andrew Morton]

On Thu, 29 May 2014 11:19:27 +0400 Konstantin Khlebnikov <koct9i@gmail.com> wrote:

> On Thu, May 29, 2014 at 3:09 AM, Andrew Morton
> <akpm@linux-foundation.org> wrote:
> > On Wed, 28 May 2014 11:59:55 +0400 Konstantin Khlebnikov <koct9i@gmail.com> wrote:
> >
> >> try_to_munlock() searches other mlocked vmas, it never unmaps pages.
> >> There is no reason for invalidation because ptes are left unchanged.
> >>
> >> ...
> >>
> >> --- a/mm/rmap.c
> >> +++ b/mm/rmap.c
> >> @@ -1225,7 +1225,7 @@ int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
> >>
> >>  out_unmap:
> >>       pte_unmap_unlock(pte, ptl);
> >> -     if (ret != SWAP_FAIL)
> >> +     if (ret != SWAP_FAIL && TTU_ACTION(flags) != TTU_MUNLOCK)
> >>               mmu_notifier_invalidate_page(mm, address);
> >>  out:
> >>       return ret;
> >
> > The patch itself looks reasonable but there is no such thing as
> > try_to_munlock().  I rewrote the changelog thusly:
> 
> Wait, what? I do have function with this name in my sources. It calls rmap_walk
> with callback try_to_unmap_one and action TTU_MUNLOCK. This is the place
> where TTU_MUNLOCK is used, I've mentioned it as entry point of this logic.

Ah OK, I obviously misgrepped.

> >
> > : In its munmap mode, try_to_unmap_one() searches other mlocked vmas, it
> > : never unmaps pages.  There is no reason for invalidation because ptes are
> > : left unchanged.
> >
> > Also, the name try_to_unmap_one() is now pretty inaccurate/incomplete.
> > Perhaps if someone is feeling enthusiastic they might think up a better
> > name for the various try_to_unmap functions and see if we can
> > appropriately document try_to_unmap_one().
> 
> I thought about moving mlock part out of try_to_unmap_one() into
> separate function,
> but normal unmap needs this part too...

try_to_unmap_one() does appear to have enough in common with the
munlock operation to justify using common code.  But doing so makes the
name wrong.

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