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@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Wed, 28 May 2014 11:59:55 +0400 Konstantin Khlebnikov <koct9i@xxxxxxxxx> 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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