From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bob Peterson Date: Fri, 21 Jul 2017 09:26:04 -0400 (EDT) Subject: [Cluster-devel] [PATCH v2] gfs2: add flag REQ_PRIO for metadata I/O In-Reply-To: <20170720154809.14445-1-colyli@suse.de> Message-ID: <977423320.33459815.1500643564867.JavaMail.zimbra@redhat.com> List-Id: To: cluster-devel.redhat.com MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit From: Coly Li When gfs2 does metadata I/O, only REQ_META is used as a metadata hint of the bio. But flag REQ_META is just a hint for block trace, not for block layer code to handle a bio as metadata request. For some of metadata I/Os of gfs2, A REQ_PRIO flag on the metadata bio would be very informative to block layer code. For example, if bcache is used as a I/O cache for gfs2, it will be possible for bcache code to get the hint and cache the pre-fetched metadata blocks on cache device. This behavior may be helpful to improve metadata I/O performance if the following requests hit the cache. Here are the locations in gfs2 code where a REQ_PRIO flag should be added, - All places where REQ_READAHEAD is used, gfs2 code uses this flag for metadata read ahead. - In gfs2_meta_rq() where the first metadata block is read in. - In gfs2_write_buf_to_page(), read in quota metadata blocks to have them up to date. These metadata blocks are probably to be accessed again in future, adding a REQ_PRIO flag may have bcache to keep such metadata in fast cache device. For system without a cache layer, REQ_PRIO can still provide hint to block layer to handle metadata requests more properly. Signed-off-by: Coly Li Cc: Eric Wheeler Cc: Bob Peterson Cc: Steven Whitehouse --- Hi, Thanks. This is now applied to the for-next branch of the linux-gfs2 tree: https://git.kernel.org/pub/scm/linux/kernel/git/gfs2/linux-gfs2.git/commit/fs/gfs2?h=for-next&id=e477b24b507998bc6568316a2e034025960d2404 Regards, Bob Peterson Red Hat File Systems