On Sat, 23 Jul 2011 20:49:10 +0200 Jens Axboe <jaxboe@xxxxxxxxxxxx> wrote: > > I can observe the average request size changes. Before the patch, the > > average request size is about 90k from iostat (but the variation is > > big). With the patch, the request size is about 100k and variation is > > small. > > That's a good win right there, imho. yup. Reduced CPU consumption on that path isn't terribly exciting IMO, but improved request size is significant. Using an additional 44 bytes of stack on that path is also significant(ly bad). But we need to fix that problem anyway. One way we could improve things in mm/vmscan.c is to move the blk_plug into scan_control then get the scan_control off the stack in some manner. That's easy for kswapd: allocate one scan_control per kswapd at startup. Doing it for direct-reclaim would be a bit trickier... And I have the usual maintainability whine. If someone comes up to vmscan.c and sees it calling blk_start_plug(), how are they supposed to work out why that call is there? They go look at the blk_start_plug() definition and it is undocumented. I think we can do better than this? -- 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>