Messages in this thread | | | Date | Tue, 3 May 2011 13:17:20 +0900 | Subject | Re: [RFC][PATCH] mm: cut down __GFP_NORETRY page allocation failures | From | Minchan Kim <> |
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On Tue, May 3, 2011 at 12:51 PM, Wu Fengguang <fengguang.wu@intel.com> wrote: > 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 >
Of course. I will try it in my better machine i5 4 core 3G ram.
> 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.
If so, I guess the workload might depend on order-0 page, not stack allocation.
> >> > 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 :)
Anyway, the problem about draining overhead with __GFP_NORETRY is valuable, I think. We should handle it
> > Thanks, > Fengguang >
Thanks for the good experiments and numbers.
-- Kind regards, Minchan Kim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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