Hi Wu, > On Mon, May 02, 2011 at 09:29:58PM +0800, Wu Fengguang wrote: > > > > + if (preferred_zone && > > > > + zone_watermark_ok_safe(preferred_zone, sc->order, > > > > + high_wmark_pages(preferred_zone), > > > > + zone_idx(preferred_zone), 0)) > > > > + goto out; > > > > + } > > > > > > As I said, I think direct reclaim path sould be fast if possbile and > > > it should not a function of min_free_kbytes. > > > > It can be made not a function of min_free_kbytes by simply changing > > high_wmark_pages() to low_wmark_pages() in the above chunk, since > > direct reclaim is triggered when ALLOC_WMARK_LOW cannot be satisfied, > > ie. it just dropped below low_wmark_pages(). > > > > But still, it costs 62ms reclaim latency (base kernel is 29ms). > > I got new findings: the CPU schedule delays are much larger than > reclaim delays. It does make the "direct reclaim until low watermark > OK" latency less a problem :) > > 1000 dd test case: > RECLAIM delay CPU delay nr_alloc_fail CAL (last CPU) > base kernel 29ms 244ms 14586 218440 > patched 62ms 215ms 5004 325 Hmm, in your system, the latency of direct reclaim may be a less problem. But, generally speaking, in a latency sensitive system in enterprise area there are two kind of processes. One is latency sensitive -(A) the other is not-latency sensitive -(B). And usually we set cpu affinity for both processes to avoid scheduling issue in (A). In this situation, CPU delay tends to be lower than the above and a less problem but reclaim delay is more critical. Regards, Satoru > > Thanks, > Fengguang > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx 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