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Date: Thu, 1 Mar 2012 13:22:15 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Jan Kara <jack@suse.cz>
Cc: Fengguang Wu <fengguang.wu@intel.com>, Greg Thelen <gthelen@google.com>,
        Ying Han <yinghan@google.com>,
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        Minchan Kim <minchan.kim@gmail.com>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 5/9] writeback: introduce the pageout work
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On Thu, 1 Mar 2012 22:15:51 +0100
Jan Kara <jack@suse.cz> wrote:

> On Thu 01-03-12 11:42:01, Andrew Morton wrote:
> > On Thu, 1 Mar 2012 12:04:04 +0100
> > Jan Kara <jack@suse.cz> wrote:
> > 
> > > > iirc, the way I "grabbed" the page was to actually lock it, with
> > > > [try_]_lock_page().  And unlock it again way over within the writeback
> > > > thread.  I forget why I did it this way, rather than get_page() or
> > > > whatever.  Locking the page is a good way of preventing anyone else
> > > > from futzing with it.  It also pins the inode, which perhaps meant that
> > > > with careful management, I could avoid the igrab()/iput() horrors
> > > > discussed above.
> > >
> > >   I think using get_page() might be a good way to go.
> > 
> > get_page() doesn't pin the inode - truncate() will still detach it
> > from the address_space().
>   Yes, I know. And exactly because of that I'd like to use it. Flusher
> thread would lock the page from the work item, check whether it is still
> attached to the inode and if yes, it will proceed. Otherwise it will just
> discard the work item because we know the page has already been written out
> by someone else or truncated.

That would work OK.  The vmscanning process won't know that its
writeback effort failed, but it's hard to see how that could cause a
problem.