linux-kernel - Re: [PATCH 2/9] mm: remap_file

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Date:	Wed, 02 Jan 2013 19:31:01 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Michel Lespinasse <walken@...gle.com>
CC:	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...nel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Hugh Dickins <hughd@...gle.com>, Jorn_Engel <joern@...fs.org>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/9] mm: remap_file_pages() fixes

On 12/20/2012 07:49 PM, Michel Lespinasse wrote:
> Assorted small fixes. The first two are quite small:
>
> - Move check for vma->vm_private_data && !(vma->vm_flags & VM_NONLINEAR)
>    within existing if (!(vma->vm_flags & VM_NONLINEAR)) block.
>    Purely cosmetic.
>
> - In the VM_LOCKED case, when dropping PG_Mlocked for the over-mapped
>    range, make sure we own the mmap_sem write lock around the
>    munlock_vma_pages_range call as this manipulates the vma's vm_flags.
>
> Last fix requires a longer explanation. remap_file_pages() can do its work
> either through VM_NONLINEAR manipulation or by creating extra vmas.
> These two cases were inconsistent with each other (and ultimately, both wrong)
> as to exactly when did they fault in the newly mapped file pages:
>
> - In the VM_NONLINEAR case, new file pages would be populated if
>    the MAP_NONBLOCK flag wasn't passed. If MAP_NONBLOCK was passed,
>    new file pages wouldn't be populated even if the vma is already
>    marked as VM_LOCKED.
>
> - In the linear (emulated) case, the work is passed to the mmap_region()
>    function which would populate the pages if the vma is marked as
>    VM_LOCKED, and would not otherwise - regardless of the value of the
>    MAP_NONBLOCK flag, because MAP_POPULATE wasn't being passed to
>    mmap_region().
>
> The desired behavior is that we want the pages to be populated and locked
> if the vma is marked as VM_LOCKED, or to be populated if the MAP_NONBLOCK
> flag is not passed to remap_file_pages().
>
> Signed-off-by: Michel Lespinasse <walken@...gle.com>

Acked-by: Rik van Riel <riel@...hat.com>

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