From: Trond Myklebust <trond.myklebust@fys.uio.no>
To: Ethan Solomita <solo@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org
Subject: Re: NR_UNSTABLE_FS vs. NR_FILE_DIRTY: double counting pages?
Date: Sun, 29 Apr 2007 21:51:29 -0400 [thread overview]
Message-ID: <1177897889.6400.49.camel@heimdal.trondhjem.org> (raw)
In-Reply-To: <463537C2.5050804@google.com>
On Sun, 2007-04-29 at 17:26 -0700, Ethan Solomita wrote:
> Trond Myklebust wrote:
> > On Fri, 2007-04-27 at 18:21 -0700, Ethan Solomita wrote:
> >> There are several places where we add together NR_UNSTABLE_FS and
> >> NF_FILE_DIRTY:
> >>
> >> sync_inodes_sb()
> >> balance_dirty_pages()
> >> wakeup_pdflush()
> >> wb_kupdate()
> >> prefetch_suitable()
> >>
> >> I can trace a standard codepath where it seems both of these are set
> >> on the same page:
> >>
> >> nfs_file_aops.commit_write ->
> >> nfs_commit_write
> >> nfs_updatepages
> >> nfs_writepage_setup
> >> nfs_wb_page
> >> nfs_wb_page_priority
> >> nfs_writepage_locked
> >> nfs_flush_mapping
> >> nfs_flush_list
> >> nfs_flush_multi
> >> nfs_write_partial_ops.rpc_call_done
> >> nfs_writeback_done_partial
> >> nfs_writepage_release
> >> nfs_reschedule_unstable_write
> >> nfs_mark_request_commit
> >> incr NR_UNSTABLE_NFS
> >>
> >> nfs_file_aops.commit_write ->
> >> nfs_commit_write
> >> nfs_updatepage
> >> __set_page_dirty_nobuffers
> >> incr NF_FILE_DIRTY
> >>
> >>
> >> This is the standard code path that derives from sys_write(). Can
> >> someone either show how this code sequence can't happen, or confirm for
> >> me that there's a bug?
> >> -- Ethan
> >
> > It should not happen. If the page is on the unstable list, then it will
> > be committed before nfs_updatepage is allowed to redirty it. See the
> > recent fixes in 2.6.21-rc7.
>
> Above I present a codepath called straight from sys_write() which seems
> to do what I say. I could be wrong, but can you address the code paths I
> show above which seem to set both?
> -- Ethan
Look carefully at nfs_update_request(): if !nfs_dirty_request(), then it
returns -EBUSY, and so nfs_writepage_setup() will loop on nfs_wb_page().
IOW: if PG_NEED_COMMIT is set (which it should be if on the commit list)
then nfs_writepage_setup() will loop...
Trond
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prev parent reply other threads:[~2007-04-30 1:51 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-04-28 1:21 Ethan Solomita
2007-04-29 20:22 ` Trond Myklebust
2007-04-30 0:26 ` Ethan Solomita
2007-04-30 1:15 ` Ethan Solomita
2007-04-30 1:51 ` Trond Myklebust [this message]
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