linux-kernel - Re: [PATCH] mm: dont call mmu_notifier_invalidate

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Date:	Wed, 28 May 2014 16:09:48 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Konstantin Khlebnikov <koct9i@...il.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: dont call mmu_notifier_invalidate_page during
 munlock

On Wed, 28 May 2014 11:59:55 +0400 Konstantin Khlebnikov <koct9i@...il.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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