Messages in this thread | | | Date | Thu, 9 Jul 2009 19:58:59 +0900 | Subject | Re: [RFC PATCH 2/2] Don't continue reclaim if the system have plenty free memory | From | Minchan Kim <> |
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On Thu, Jul 9, 2009 at 2:08 PM, KOSAKI Motohiro<kosaki.motohiro@jp.fujitsu.com> wrote: >> Hi, Kosaki. >> >> On Tue, Jul 7, 2009 at 6:48 PM, KOSAKI >> Motohiro<kosaki.motohiro@jp.fujitsu.com> wrote: >> > Subject: [PATCH] Don't continue reclaim if the system have plenty free memory >> > >> > On concurrent reclaim situation, if one reclaimer makes OOM, maybe other >> > reclaimer can stop reclaim because OOM killer makes enough free memory. >> > >> > But current kernel doesn't have its logic. Then, we can face following accidental >> > 2nd OOM scenario. >> > >> > 1. System memory is used by only one big process. >> > 2. memory shortage occur and concurrent reclaim start. >> > 3. One reclaimer makes OOM and OOM killer kill above big process. >> > 4. Almost reclaimable page will be freed. >> > 5. Another reclaimer can't find any reclaimable page because those pages are >> > ? already freed. >> > 6. Then, system makes accidental and unnecessary 2nd OOM killer. >> > >> >> Did you see the this situation ? >> Why I ask is that we have already a routine for preventing parallel >> OOM killing in __alloc_pages_may_oom. >> >> Couldn't it protect your scenario ? > > Can you please see actual code of this patch?
I mean follow as,
static inline struct page * __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order, struct zonelist *zonelist, enum zone_type high_zoneidx, ... <snip>
/* * Go through the zonelist yet one more time, keep very high watermark * here, this is only to catch a parallel oom killing, we must fail if * we're still under heavy pressure. */ page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, nodemask, order, zonelist, high_zoneidx, ALLOC_WMARK_HIGH|ALLOC_CPUSET, preferred_zone, migratetype);
> Those two patches fix different problem. > > 1/2 fixes the issue of that concurrent direct reclaimer makes > too many isolated pages. > 2/2 fixes the issue of that reclaim and exit race makes accidental oom. > > >> If it can't, Could you explain the scenario in more detail ? > > __alloc_pages_may_oom() check don't effect the threads of already > entered reclaim. it's obvious.
Threads which are entered into direct reclaim mode will call __alloc_pages_may_oom before out_of_memory. At that time, if one big process is killed a while ago, get_page_from_freelist in __alloc_pages_may_oom will be succeeded at last. So I think it doesn't occur OOM.
But in that case, we suffered from unnecessary page scanning per each priority(12~0). So in this case, your patch is good to me. then you would be better to change log. :)
-- Kind regards, Minchan Kim
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