On 05/21/2012 05:09 PM, ehrhardt@xxxxxxxxxxxxxxxxxx wrote: > From: Christian Ehrhardt <ehrhardt@xxxxxxxxxxxxxxxxxx> > > Swap readahead works fine, but the I/O to disk is almost always done in page > size requests, despite the fact that readahead submits 1<<page-cluster pages > at a time. > On older kernels the old per device plugging behavior might have captured > this and merged the requests, but currently all comes down to much more I/Os > than required. > > On a single device this might not be an issue, but as soon as a server runs > on shared san resources savin I/Os not only improves swapin throughput but > also provides a lower resource utilization. > > With a load running KVM in a lot of memory overcommitment (the hot memory > is 1.5 times the host memory) swapping throughput improves significantly > and the lead feels more responsive as well as achieves more throughput. > > In a test setup with 16 swap disks running blocktrace on one of those disks > shows the improved merging: > Prior: > Reads Queued: 560,888, 2,243MiB Writes Queued: 226,242, 904,968KiB > Read Dispatches: 544,701, 2,243MiB Write Dispatches: 159,318, 904,968KiB > Reads Requeued: 0 Writes Requeued: 0 > Reads Completed: 544,716, 2,243MiB Writes Completed: 159,321, 904,980KiB > Read Merges: 16,187, 64,748KiB Write Merges: 61,744, 246,976KiB > IO unplugs: 149,614 Timer unplugs: 2,940 > > With the patch: > Reads Queued: 734,315, 2,937MiB Writes Queued: 300,188, 1,200MiB > Read Dispatches: 214,972, 2,937MiB Write Dispatches: 215,176, 1,200MiB > Reads Requeued: 0 Writes Requeued: 0 > Reads Completed: 214,971, 2,937MiB Writes Completed: 215,177, 1,200MiB > Read Merges: 519,343, 2,077MiB Write Merges: 73,325, 293,300KiB > IO unplugs: 337,130 Timer unplugs: 11,184 > > Signed-off-by: Christian Ehrhardt <ehrhardt@xxxxxxxxxxxxxxxxxx> > Acked-by: Rik van Riel <riel@xxxxxxxxxx> > Acked-by: Jens Axboe <axboe@xxxxxxxxx> Reviewed-by: Minchan Kim <minchan@xxxxxxxxxx> Didn't I add my Reviewed-by on your previous version? -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>