linux-kernel - Re: [PATCH 4/7] Use vfs __set_page_dirty interface instead of doing it inside filesystem

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Date:	Thu, 5 Jul 2012 23:40:07 +0800
From:	Sha Zhengju <handai.szj@...il.com>
To:	Sage Weil <sage@...tank.com>
Cc:	linux-mm@...ck.org, cgroups@...r.kernel.org,
	kamezawa.hiroyu@...fujitsu.com, gthelen@...gle.com,
	yinghan@...gle.com, akpm@...ux-foundation.org, mhocko@...e.cz,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	viro@...iv.linux.org.uk, linux-fsdevel@...r.kernel.org,
	sage@...dream.net, ceph-devel@...r.kernel.org,
	Sha Zhengju <handai.szj@...bao.com>
Subject: Re: [PATCH 4/7] Use vfs __set_page_dirty interface instead of doing
 it inside filesystem

On Thu, Jul 5, 2012 at 11:20 PM, Sage Weil <sage@...tank.com> wrote:
> On Wed, 4 Jul 2012, Sha Zhengju wrote:
>> On 07/02/2012 10:49 PM, Sage Weil wrote:
>> > On Mon, 2 Jul 2012, Sha Zhengju wrote:
>> > > On 06/29/2012 01:21 PM, Sage Weil wrote:
>> > > > On Thu, 28 Jun 2012, Sha Zhengju wrote:
>> > > >
>> > > > > From: Sha Zhengju<handai.szj@...bao.com>
>> > > > >
>> > > > > Following we will treat SetPageDirty and dirty page accounting as an
>> > > > > integrated
>> > > > > operation. Filesystems had better use vfs interface directly to avoid
>> > > > > those details.
>> > > > >
>> > > > > Signed-off-by: Sha Zhengju<handai.szj@...bao.com>
>> > > > > ---
>> > > > >    fs/buffer.c                 |    2 +-
>> > > > >    fs/ceph/addr.c              |   20 ++------------------
>> > > > >    include/linux/buffer_head.h |    2 ++
>> > > > >    3 files changed, 5 insertions(+), 19 deletions(-)
>> > > > >
>> > > > > diff --git a/fs/buffer.c b/fs/buffer.c
>> > > > > index e8d96b8..55522dd 100644
>> > > > > --- a/fs/buffer.c
>> > > > > +++ b/fs/buffer.c
>> > > > > @@ -610,7 +610,7 @@ EXPORT_SYMBOL(mark_buffer_dirty_inode);
>> > > > >     * If warn is true, then emit a warning if the page is not uptodate
>> > > > > and
>> > > > > has
>> > > > >     * not been truncated.
>> > > > >     */
>> > > > > -static int __set_page_dirty(struct page *page,
>> > > > > +int __set_page_dirty(struct page *page,
>> > > > >               struct address_space *mapping, int warn)
>> > > > >    {
>> > > > >       if (unlikely(!mapping))
>> > > > This also needs an EXPORT_SYMBOL(__set_page_dirty) to allow ceph to
>> > > > continue to build as a module.
>> > > >
>> > > > With that fixed, the ceph bits are a welcome cleanup!
>> > > >
>> > > > Acked-by: Sage Weil<sage@...tank.com>
>> > > Further, I check the path again and may it be reworked as follows to avoid
>> > > undo?
>> > >
>> > > __set_page_dirty();
>> > > __set_page_dirty();
>> > > ceph operations;                ==>                     if (page->mapping)
>> > > if (page->mapping)                                            ceph
>> > > operations;
>> > >      ;
>> > > else
>> > >      undo = 1;
>> > > if (undo)
>> > >      xxx;
>> > Yep.  Taking another look at the original code, though, I'm worried that
>> > one reason the __set_page_dirty() actions were spread out the way they are
>> > is because we wanted to ensure that the ceph operations were always
>> > performed when PagePrivate was set.
>> >
>>
>> Sorry, I've lost something:
>>
>> __set_page_dirty();                        __set_page_dirty();
>> ceph operations;
>> if(page->mapping)         ==>      if(page->mapping) {
>>        SetPagePrivate;                            SetPagePrivate;
>> else                                                      ceph operations;
>>     undo = 1;                                  }
>>
>> if (undo)
>>     XXX;
>>
>> I think this can ensure that ceph operations are performed together with
>> SetPagePrivate.
>
> Yeah, that looks right, as long as the ceph accounting operations happen
> before SetPagePrivate.  I think it's no more or less racy than before, at
> least.
>
> The patch doesn't apply without the previous ones in the series, it looks
> like.  Do you want to prepare a new version or should I?
>

Good. I'm doing some test then I'll send out a new version patchset, please
wait a bit. : )


Thanks,
Sha
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