linux-kernel - Re: [PATCH+comment] fix tmpfs BUG and AOP_WRITEPAGE

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Message-ID: <84144f020710242237q3aa8e96dtc8cf3f02f2af2cc9@mail.gmail.com>
Date:	Thu, 25 Oct 2007 08:37:26 +0300
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Hugh Dickins" <hugh@...itas.com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>, ezk@...sunysb.edu,
	ryan@...nie.org, mhalcrow@...ibm.com, cjwatson@...ntu.com,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, stable@...nel.org
Subject: Re: [PATCH+comment] fix tmpfs BUG and AOP_WRITEPAGE_ACTIVATE

Hi Hugh,

On 10/25/07, Hugh Dickins <hugh@...itas.com> wrote:
> --- 2.6.24-rc1/mm/shmem.c       2007-10-24 07:16:04.000000000 +0100
> +++ linux/mm/shmem.c    2007-10-24 22:31:09.000000000 +0100
> @@ -915,6 +915,21 @@ static int shmem_writepage(struct page *
>         struct inode *inode;
>
>         BUG_ON(!PageLocked(page));
> +       /*
> +        * shmem_backing_dev_info's capabilities prevent regular writeback or
> +        * sync from ever calling shmem_writepage; but a stacking filesystem
> +        * may use the ->writepage of its underlying filesystem, in which case

I find the above bit somewhat misleading as it implies that the
!wbc->for_reclaim case can be removed after ecryptfs has similar fix
as unionfs. Can we just say that while BDI_CAP_NO_WRITEBACK does
prevent some callers from entering ->writepage(), it's just an
optimization and ->writepage() must deal with !wbc->for_reclaim case
properly?

                                          Pekka
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