From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ming Lei Date: Thu, 22 Nov 2018 18:26:17 +0800 Subject: [Cluster-devel] [PATCH V11 14/19] block: handle non-cluster bio out of blk_bio_segment_split In-Reply-To: <20181122100427.GA28871@lst.de> References: <20181121032327.8434-1-ming.lei@redhat.com> <20181121032327.8434-15-ming.lei@redhat.com> <20181121143355.GB2594@lst.de> <20181121153726.GC19111@ming.t460p> <20181121174621.GA6961@lst.de> <20181122093259.GA27007@ming.t460p> <20181122100427.GA28871@lst.de> Message-ID: <20181122102616.GC27273@ming.t460p> List-Id: To: cluster-devel.redhat.com MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Thu, Nov 22, 2018 at 11:04:28AM +0100, Christoph Hellwig wrote: > On Thu, Nov 22, 2018 at 05:33:00PM +0800, Ming Lei wrote: > > However, using virt boundary limit on non-cluster seems over-kill, > > because the bio will be over-split(each small bvec may be split as one bio) > > if it includes lots of small segment. > > The combination of the virt boundary of PAGE_SIZE - 1 and a > max_segment_size of PAGE_SIZE will only split if the to me merged > segment is in a different page than the previous one, which is exactly > what we need here. Multiple small bvec inside the same page (e.g. > 512 byte buffer_heads) will still be merged. Suppose one bio includes (pg0, 0, 512) and (pg1, 512, 512): The split is introduced by the following code in blk_bio_segment_split(): if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset)) goto split; Without this patch, for non-cluster, the two bvecs are just in different segment, but still handled by one same bio. Now you convert into two bios. Thanks, Ming