From: Suparna Bhattacharya <suparna@in.ibm.com>
To: Andrew Morton <akpm@osdl.org>
Cc: daniel@osdl.org, janetmor@us.ibm.com, pbadari@us.ibm.com,
linux-aio@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH linux-2.6.0-test10-mm1] filemap_fdatawait.patch
Date: Wed, 31 Dec 2003 15:25:03 +0530 [thread overview]
Message-ID: <20031231095503.GA4069@in.ibm.com> (raw)
In-Reply-To: <20031231013521.79920efd.akpm@osdl.org>
On Wed, Dec 31, 2003 at 01:35:21AM -0800, Andrew Morton wrote:
> Suparna Bhattacharya <suparna@in.ibm.com> wrote:
> >
> > It seems like the case Daniel is thinking about is when
> > a process has issued writes to the page cache, and then filemap_fdatawrite
> > is called, while these pages are being written back to disk parallely by
> > another thread (not holding i_sem). The filemap_fdatawrite wouldn't see
> > pages that are in the process of being written out by the background
> > thread so it doesn't mark them for writeback.
>
> If those pages are under writeout then they are clean and
> filemap_fdatawrite() has nothing to do.
Sure, it doesn't, because the other thread is about to issue
a writeout on them. But it does mean that there is no guarantee
that those pages are already marked as writeback when
filemap_fdatawrite returns and filemap_fdatawait is called.
>
> If, however, those pages were redirtied while under I/O then they are
> dirty, on dirty_pages and are under writeout. In that case
> filemap_fdatawrite() must wait for the current write to complete and must
> start a new write.
>
> > The following filemap_fdatawait
> > would find these pages on the locked_pages list all right, but if its
> > unlucky enough to be in the window that Daniel mentions where PG_dirty
> > is cleared but PG_writeback hasn't yet been set, then the page would
> > have move to the clean list without waiting for the actual writeout
> > to complete !
>
> If you are referring to this code in mpage_writepage():
>
> lock_page(page);
>
> if (wbc->sync_mode != WB_SYNC_NONE)
> wait_on_page_writeback(page);
>
> if (page->mapping == mapping && !PageWriteback(page) &&
> test_clear_page_dirty(page)) {
>
>
> then I don't see the race - the page lock synchronises the two threads?
>
But filemap_fdatawait does not look at the page lock. So there's a
tiny window when the page is on locked_pages with PG_dirty cleared
and PG_writeback not set. Does that make sense, or is there something
I overlook ?
Daniel's patch precisely tried to fill that gap - he added a check for page
lock in filemap_datawait.
Regards
Suparna
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-aio' in
> the body to majordomo@kvack.org. For more info on Linux AIO,
> see: http://www.kvack.org/aio/
> Don't email: <a href=mailto:"aart@kvack.org">aart@kvack.org</a>
--
Suparna Bhattacharya (suparna@in.ibm.com)
Linux Technology Center
IBM Software Lab, India
next prev parent reply other threads:[~2003-12-31 9:49 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <3FCD4B66.8090905@us.ibm.com>
2003-12-06 1:29 ` [PATCH linux-2.6.0-test10-mm1] dio-read-race-fix Daniel McNeil
2003-12-08 18:23 ` Daniel McNeil
2003-12-12 0:51 ` Daniel McNeil
2003-12-17 1:25 ` [PATCH linux-2.6.0-test10-mm1] filemap_fdatawait.patch Daniel McNeil
2003-12-17 2:03 ` Andrew Morton
2003-12-17 19:25 ` Daniel McNeil
2003-12-17 20:17 ` Janet Morgan
2003-12-31 9:18 ` Suparna Bhattacharya
2003-12-31 9:35 ` Andrew Morton
2003-12-31 9:55 ` Suparna Bhattacharya [this message]
2003-12-31 9:59 ` Andrew Morton
2003-12-31 10:09 ` Suparna Bhattacharya
2003-12-31 10:10 ` Andrew Morton
2003-12-31 10:48 ` Suparna Bhattacharya
2003-12-31 10:53 ` Andrew Morton
2003-12-31 10:54 ` Andrew Morton
2003-12-31 11:17 ` Andrew Morton
2003-12-31 22:34 ` [PATCH linux-2.6.1-rc1-mm1] filemap_fdatawait.patch Daniel McNeil
2003-12-31 22:41 ` [PATCH linux-2.6.1-rc1-mm1] aiodio_fallback_bio_count.patch Daniel McNeil
2003-12-31 23:46 ` Andrew Morton
2004-01-02 5:14 ` Suparna Bhattacharya
2004-01-02 7:46 ` Andrew Morton
2004-01-05 3:55 ` Suparna Bhattacharya
2004-01-05 5:06 ` Andrew Morton
2004-01-05 5:28 ` Suparna Bhattacharya
2004-01-05 5:28 ` Andrew Morton
2004-01-05 6:06 ` Suparna Bhattacharya
2004-01-05 6:14 ` Lincoln Dale
2003-12-31 22:47 ` [PATCH linux-2.6.1-rc1-mm1] dio_isize.patch Daniel McNeil
2003-12-31 23:42 ` [PATCH linux-2.6.1-rc1-mm1] filemap_fdatawait.patch Andrew Morton
2004-01-02 4:20 ` Suparna Bhattacharya
2004-01-02 4:36 ` Andrew Morton
2004-01-02 5:50 ` [PATCH linux-2.6.0-test10-mm1] filemap_fdatawait.patch Suparna Bhattacharya
2004-01-02 7:31 ` Andrew Morton
2004-01-05 13:49 ` Marcelo Tosatti
2004-01-05 20:27 ` Andrew Morton
2004-03-29 15:44 ` Marcelo Tosatti
2004-01-11 23:14 ` Janet Morgan
2004-01-11 23:44 ` Andrew Morton
2004-01-12 18:00 ` filemap_fdatawait.patch Daniel McNeil
2004-01-12 19:39 ` [PATCH linux-2.6.0-test10-mm1] filemap_fdatawait.patch Janet Morgan
2004-01-12 19:46 ` Daniel McNeil
2004-01-13 4:12 ` Janet Morgan
2003-12-30 4:53 ` [PATCH linux-2.6.0-test10-mm1] dio-read-race-fix Suparna Bhattacharya
2003-12-31 0:29 ` Daniel McNeil
2003-12-31 6:09 ` Suparna Bhattacharya
2004-01-08 23:55 ` Daniel McNeil
2004-01-09 3:55 ` Suparna Bhattacharya
2004-02-05 1:39 ` [PATCH 2.6.2-rc3-mm1] DIO read race fix Daniel McNeil
2004-02-05 1:54 ` Badari Pulavarty
2004-02-05 2:07 ` Andrew Morton
2004-02-05 2:54 ` Janet Morgan
2004-02-05 3:19 ` Andrew Morton
2004-02-05 3:43 ` Suparna Bhattacharya
2004-02-05 5:33 ` Andrew Morton
2004-02-05 17:52 ` Daniel McNeil
2004-02-05 18:53 ` Badari Pulavarty
2004-03-29 15:41 ` [PATCH linux-2.6.0-test10-mm1] dio-read-race-fix Suparna Bhattacharya
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