Hi Minchan, On Tue, May 03, 2011 at 08:49:20AM +0800, Minchan Kim wrote: > Hi Wu, Sorry for slow response. > I guess you know why I am slow. :) Yeah, never mind :) > Unfortunately, my patch doesn't consider order-0 pages, as you mentioned below. > I read your mail which states it doesn't help although it considers > order-0 pages and drain. > Actually, I tried to look into that but in my poor system(core2duo, 2G > ram), nr_alloc_fail never happens. :( I'm running a 4-core 8-thread CPU with 3G ram. Did you run with this patch? [PATCH] mm: readahead page allocations are OK to fail https://lkml.org/lkml/2011/4/26/129 It's very good at generating lots of __GFP_NORETRY order-0 page allocation requests. > I will try it in other desktop but I am not sure I can reproduce it. > > > > > root@fat /home/wfg# ./test-dd-sparse.sh > > start time: 246 > > total time: 531 > > nr_alloc_fail 14097 > > allocstall 1578332 > > LOC: 542698 538947 536986 567118 552114 539605 541201 537623 Local timer interrupts > > RES: 3368 1908 1474 1476 2809 1602 1500 1509 Rescheduling interrupts > > CAL: 223844 224198 224268 224436 223952 224056 223700 223743 Function call interrupts > > TLB: 381 27 22 19 96 404 111 67 TLB shootdowns > > > > root@fat /home/wfg# getdelays -dip `pidof dd` > > print delayacct stats ON > > printing IO accounting > > PID 5202 > > > > > > CPU count real total virtual total delay total > > 1132 3635447328 3627947550 276722091605 > > IO count delay total delay average > > 2 187809974 62ms > > SWAP count delay total delay average > > 0 0 0ms > > RECLAIM count delay total delay average > > 1334 35304580824 26ms > > dd: read=278528, write=0, cancelled_write=0 > > > > I guess your patch is mainly fixing the high order allocations while > > my workload is mainly order 0 readahead page allocations. There are > > 1000 forks, however the "start time: 246" seems to indicate that the > > order-1 reclaim latency is not improved. > > Maybe, 8K * 1000 isn't big footprint so I think reclaim doesn't happen. It's mainly a guess. In an earlier experiment of simply increasing nr_to_reclaim to high_wmark_pages() without any other constraints, it does manage to reduce start time to about 25 seconds. > > I'll try modifying your patch and see how it works out. The obvious > > change is to apply it to the order-0 case. Hope this won't create much > > more isolated pages. > > > > Attached is your patch rebased to 2.6.39-rc3, after resolving some > > merge conflicts and fixing a trivial NULL pointer bug. > > Thanks! > I would like to see detail with it in my system if I can reproduce it. OK. > >> > no cond_resched(): > >> > >> What's this? > > > > I tried a modified patch that also removes the cond_resched() call in > > __alloc_pages_direct_reclaim(), between try_to_free_pages() and > > get_page_from_freelist(). It seems not helping noticeably. > > > > It looks safe to remove that cond_resched() as we already have such > > calls in shrink_page_list(). > > I tried similar thing but Andrew have a concern about it. > https://lkml.org/lkml/2011/3/24/138 Yeah cond_resched() is at least not the root cause of our problems.. > >> > + if (total_scanned > 2 * sc->nr_to_reclaim) > >> > + goto out; > >> > >> If there are lots of dirty pages in LRU? > >> If there are lots of unevictable pages in LRU? > >> If there are lots of mapped page in LRU but may_unmap = 0 cases? > >> I means it's rather risky early conclusion. > > > > That test means to avoid scanning too much on __GFP_NORETRY direct > > reclaims. My assumption for __GFP_NORETRY is, it should fail fast when > > the LRU pages seem hard to reclaim. And the problem in the 1000 dd > > case is, it's all easy to reclaim LRU pages but __GFP_NORETRY still > > fails from time to time, with lots of IPIs that may hurt large > > machines a lot. > > I don't have enough time and a environment to test it. > So I can't make sure of it but my concern is a latency. > If you solve latency problem considering CPU scaling, I won't oppose it. :) OK, let's head for that direction :) 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=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>