From: Jan Kara <jack@suse.cz>
To: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>, Mel Gorman <mgorman@suse.de>,
linux-mm@kvack.org
Subject: Re: Does swap_set_page_dirty() calling ->set_page_dirty() make sense?
Date: Tue, 18 Sep 2012 04:16:27 +0200 [thread overview]
Message-ID: <20120918021627.GF9150@quack.suse.cz> (raw)
In-Reply-To: <alpine.LSU.2.00.1209171204100.6720@eggly.anvils>
On Mon 17-09-12 12:15:46, Hugh Dickins wrote:
> On Mon, 17 Sep 2012, Jan Kara wrote:
> >
> > I tripped over a crash in reiserfs which happened due to PageSwapCache
> > page being passed to reiserfs_set_page_dirty(). Now it's not that hard to
> > make reiserfs_set_page_dirty() check that case but I really wonder: Does it
> > make sense to call mapping->a_ops->set_page_dirty() for a PageSwapCache
> > page? The page is going to be written via direct IO so from the POV of the
> > filesystem there's no need for any dirtiness tracking. Also there are
> > several ->set_page_dirty() implementations which will spectacularly crash
> > because they do things like page->mapping->host, or call
> > __set_page_dirty_buffers() which expects buffer heads in page->private.
> > Or what is the reason for calling filesystem's set_page_dirty() function?
>
> This is a question for Mel, really: it used not to call the filesystem.
>
> But my reading of the 3.6 code says that it still will not call the
> filesystem, unless the filesystem (only nfs) provides a swap_activate
> method, which should be the only case in which SWP_FILE gets set.
> And I rather think Mel does want to use the filesystem set_page_dirty
> in that case. Am I misreading?
>
> Did you see this on a vanilla kernel? Or is it possible that you have
> a private patch merged in, with something else sharing the SWP_FILE bit
> (defined in include/linux/swap.h) by mistake?
Argh, sorry. It is indeed a SLES specific bug. I missed that SWP_FILE bit
gets set only when swap_activate() is provided (SLES code works a bit
differently in this area but I wasn't really looking into that since I was
focused elsewhere).
So just one minor nit for Mel. SWP_FILE looks like a bit confusing name for
a flag that gets set only for some swap files ;) At least I didn't pay
attention to it because I thought it's set for all of them. Maybe call it
SWP_FILE_CALL_AOPS or something like that?
Thanks Hugh for having a look.
Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR
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next prev parent reply other threads:[~2012-09-18 2:16 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-17 16:35 Does swap_set_page_dirty() calling ->set_page_dirty() make sense? Jan Kara
2012-09-17 19:15 ` Hugh Dickins
2012-09-18 2:16 ` Jan Kara [this message]
2012-09-18 8:51 ` Petr Tesarik
2012-09-18 10:02 ` Mel Gorman
2012-09-18 9:58 ` Mel Gorman
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