Patch to issue pure flushes directly (Was: Re: [PATCH v6 0/4] ext4: Coordinate data-only flush requests sent) by fsync
From: Ted Ts'o <tytso@mit.edu>
Date: 2011-01-07 23:55:18
Also in:
dm-devel, linux-ext4, lkml
This patch seemed like a good idea to me; I just checked linux-next, and looks like nothing like this is planned to be merged. Just thought I would send a prod-o-gram to see what the current thinking was around adding something like this. Thanks, - Ted On Tue, Nov 30, 2010 at 05:41:24PM +0100, Christoph Hellwig wrote:
quoted hunk ↗ jump to hunk
FYI, here's an updated version of my patch to not run pure flushes that also works on SCSI/ATA and not just virtio. I suspect the patch alone might not be enough, but together with a variant of Neil's suggestion might do the trick, with my patch taking care of the highend-devices and Neil's scheme of taking care of stupid SATA disks. Index: linux-2.6/block/blk-flush.c ===================================================================--- linux-2.6.orig/block/blk-flush.c 2010-11-30 17:27:33.108254088 +0100 +++ linux-2.6/block/blk-flush.c 2010-11-30 17:27:38.790004333 +0100@@ -143,6 +143,17 @@ struct request *blk_do_flush(struct requ unsigned skip = 0; /* + * Just issue pure flushes directly. + */ + if (!blk_rq_sectors(rq)) { + if (!do_preflush) { + __blk_end_request_all(rq, 0); + return NULL; + } + return rq; + } + + /* * Special case. If there's data but flush is not necessary, * the request can be issued directly. *Index: linux-2.6/drivers/scsi/scsi_lib.c ===================================================================--- linux-2.6.orig/drivers/scsi/scsi_lib.c 2010-11-30 17:27:33.120254298 +0100 +++ linux-2.6/drivers/scsi/scsi_lib.c 2010-11-30 17:27:38.791003634 +0100@@ -1060,7 +1060,7 @@ int scsi_setup_blk_pc_cmnd(struct scsi_d * that does not transfer data, in which case they may optionally * submit a request without an attached bio. */ - if (req->bio) { + if (req->bio && !(req->cmd_flags & REQ_FLUSH)) { int ret; BUG_ON(!req->nr_phys_segments);