From: Andi Kleen <andi@firstfloor.org>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Quentin Barnes <qbarnes+nfs@yahoo-inc.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
linux-fsdevel@vger.kernel.org, Nick Piggin <npiggin@suse.de>,
Steven Whitehouse <swhiteho@redhat.com>
Subject: Re: [RFC][PATCH 2/2] readahead: avoid page-by-page reads on POSIX_FADV_RANDOM
Date: Wed, 30 Dec 2009 19:02:38 +0100 [thread overview]
Message-ID: <873a2s8hmp.fsf@basil.nowhere.org> (raw)
In-Reply-To: <20091230052402.GB26364@localhost> (Wu Fengguang's message of "Wed, 30 Dec 2009 13:24:02 +0800")
Wu Fengguang <fengguang.wu@intel.com> writes:
> * the ra fields can be accessed concurrently in a racy way.
> --- linux.orig/mm/fadvise.c 2009-12-30 13:02:03.000000000 +0800
> +++ linux/mm/fadvise.c 2009-12-30 13:23:05.000000000 +0800
> @@ -77,12 +77,14 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, lof
> switch (advice) {
> case POSIX_FADV_NORMAL:
> file->f_ra.ra_pages = bdi->ra_pages;
> + file->f_ra.flags &= ~RA_FLAG_RANDOM;
> break;
> case POSIX_FADV_RANDOM:
> - file->f_ra.ra_pages = 0;
> + file->f_ra.flags |= RA_FLAG_RANDOM;
What prevents this from racing with a parallel readahead
state modification, losing the bits?
-Andi
--
ak@linux.intel.com -- Speaking for myself only.
next prev parent reply other threads:[~2009-12-30 18:02 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20091225000717.GA26949@yahoo-inc.com>
[not found] ` <87aax18xms.fsf@basil.nowhere.org>
2009-12-30 5:15 ` [RFC][PATCH] Disabling read-ahead makes I/O of large reads small Wu Fengguang
2009-12-30 5:17 ` [RFC][PATCH 1/2] readahead: replace ra->mmap_miss with ra->flags Wu Fengguang
2009-12-30 5:24 ` [RFC][PATCH 2/2] readahead: avoid page-by-page reads on POSIX_FADV_RANDOM Wu Fengguang
2009-12-30 18:02 ` Andi Kleen [this message]
2009-12-31 1:39 ` Wu Fengguang
2009-12-31 2:53 ` Wu Fengguang
2009-12-31 3:03 ` Wu Fengguang
2009-12-31 4:31 ` [RFC][PATCH v2] readahead: introduce O_RANDOM_READ for POSIX_FADV_RANDOM Wu Fengguang
2010-01-08 13:08 ` Christoph Hellwig
2010-01-09 13:59 ` Wu Fengguang
2010-01-09 14:01 ` Wu Fengguang
2010-01-04 4:50 ` [RFC][PATCH v3] readahead: introduce O_RANDOM " Wu Fengguang
2010-01-04 5:17 ` Stephen Rothwell
2010-01-04 7:33 ` Christoph Hellwig
2010-01-04 12:56 ` [RFC][PATCH v4] " Wu Fengguang
2010-01-05 2:03 ` Stephen Rothwell
2010-01-05 2:26 ` Wu Fengguang
2010-01-05 2:28 ` Stephen Rothwell
2010-01-05 2:45 ` Wu Fengguang
2010-01-05 5:21 ` Eric Paris
2010-01-05 3:18 ` [RFC][PATCH v5] " Wu Fengguang
2010-01-05 3:27 ` Wu Fengguang
2010-01-04 16:50 ` [RFC][PATCH v3] " Quentin Barnes
2010-01-04 18:57 ` Andreas Dilger
2010-01-04 5:20 ` Minchan Kim
2010-01-04 12:16 ` Wu Fengguang
2010-01-05 1:46 ` Minchan Kim
2010-01-05 2:16 ` Wu Fengguang
2010-01-05 3:40 ` Minchan Kim
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