From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bob Peterson Date: Tue, 9 Jun 2015 10:45:53 -0400 (EDT) Subject: [Cluster-devel] [GFS2 PATCH] GFS2: Don't brelse rgrp buffer_heads every allocation In-Reply-To: <55758830.6080405@redhat.com> References: <40631507.11797438.1433515756742.JavaMail.zimbra@redhat.com> <55758830.6080405@redhat.com> Message-ID: <1353222669.13489616.1433861153801.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 ----- Original Message ----- > Hi, > > > On 05/06/15 15:49, Bob Peterson wrote: > > Hi, > > > > This patch allows the block allocation code to retain the buffers > > for the resource groups so they don't need to be re-read from buffer > > cache with every request. This is a performance improvement that's > > especially noticeable when resource groups are very large. For > > example, with 2GB resource groups and 4K blocks, there can be 33 > > blocks for every resource group. This patch allows those 33 buffers > > to be kept around and not read in and thrown away with every > > operation. The buffers are released when the resource group is > > either synced or invalidated. > The blocks should be cached between operations, so this should only be > resulting in a skip of the look up of the cached block, and no changes > to the actual I/O. Does that mean that grab_cache_page() is slow I > wonder? Or is this an issue of going around the retry loop due to lack > of memory at some stage? > > How does this interact with the rgrplvb support? I'd guess that with > that turned on, this is no longer an issue, because we'd only read in > the blocks for the rgrps that we are actually going to use? > > > > Steve. Hi, If you compare the two vmstat outputs in the bugzilla #1154782, you'll see no significant difference in memory usage nor cpu usage. So I assume the page lookup is the "slow" part; not because it's such a slow thing but because it's done 33 times per read-reference-invalidate (33 pages to look up per rgrp). Regards, Bob Peterson Red Hat File Systems