Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755884Ab3EHVsx (ORCPT ); Wed, 8 May 2013 17:48:53 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:32327 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755642Ab3EHVsu (ORCPT ); Wed, 8 May 2013 17:48:50 -0400 Date: Wed, 8 May 2013 14:48:45 -0700 From: "Darrick J. Wong" To: Mike Snitzer , Joe Thornber Cc: device-mapper development , linux-kernel@vger.kernel.org Subject: dm-cache not writing out cache metadata at reboot? Message-ID: <20130508214845.GA7729@blackbox.djwong.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) X-Source-IP: ucsinet21.oracle.com [156.151.31.93] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2179 Lines: 51 Hi, So I've been watching the hit/miss counters in dmcache and I've noticed a couple of things that look like errors to me: First, I noticed that if I reboot the system, neither cache_postsuspend nor cache_dtr get called. This might simply be expected behavior, but it means that the in-memory superblock structure doesn't get written out to disk upon reboot. Just to be sure, I put a printk into __commit_transaction. It prints out for 'dmsetup info' and 'dmsetup remove' but nothing at reboot. Second, cache_status calls dm_cache_commit, which writes out a superblock to the metadata device. However, there's no call to save_stats to copy the current values of the counters out to the disk's copy prior to calling dm_cache_commit. Therefore, we seem to be writing out stale copies of superblock fields. The second one seems fixable with the attached patch, but the first one I don't know about. Any ideas? --- Subject: [PATCH] dmcache: flush superblock when retrieving status info When userspace queries dmcache for stats info, we should ensure that all the metadata gets flushed out of memory to disk. The current code neglects to update at least the hit/miss counters, so take care of everything. Signed-off-by: Darrick J. Wong --- drivers/md/dm-cache-target.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c index 1074409..f476ada 100644 --- a/drivers/md/dm-cache-target.c +++ b/drivers/md/dm-cache-target.c @@ -2451,8 +2451,7 @@ static void cache_status(struct dm_target *ti, status_type_t type, case STATUSTYPE_INFO: /* Commit to ensure statistics aren't out-of-date */ if (!(status_flags & DM_STATUS_NOFLUSH_FLAG) && !dm_suspended(ti)) { - r = dm_cache_commit(cache->cmd, false); - if (r) + if (!sync_metadata(cache)) DMERR("could not commit metadata for accurate status"); } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/