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Date: Thu, 10 Sep 2009 08:58:20 +0900 (JST) From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> To: Minchan Kim <minchan.kim@...il.com> Cc: kosaki.motohiro@...fujitsu.com, Christoph Lameter <cl@...ux-foundation.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Mike Galbraith <efault@....de>, Ingo Molnar <mingo@...e.hu>, linux-mm <linux-mm@...ck.org>, Oleg Nesterov <onestero@...hat.com>, lkml <linux-kernel@...r.kernel.org> Subject: Re: [rfc] lru_add_drain_all() vs isolation > On Wed, Sep 9, 2009 at 1:27 PM, KOSAKI Motohiro > <kosaki.motohiro@...fujitsu.com> wrote: > >> The usefulness of a scheme like this requires: > >> > >> 1. There are cpus that continually execute user space code > >> without system interaction. > >> > >> 2. There are repeated VM activities that require page isolation / > >> migration. > >> > >> The first page isolation activity will then clear the lru caches of the > >> processes doing number crunching in user space (and therefore the first > >> isolation will still interrupt). The second and following isolation will > >> then no longer interrupt the processes. > >> > >> 2. is rare. So the question is if the additional code in the LRU handling > >> can be justified. If lru handling is not time sensitive then yes. > > > > Christoph, I'd like to discuss a bit related (and almost unrelated) thing. > > I think page migration don't need lru_add_drain_all() as synchronous, because > > page migration have 10 times retry. > > > > Then asynchronous lru_add_drain_all() cause > > > > - if system isn't under heavy pressure, retry succussfull. > > - if system is under heavy pressure or RT-thread work busy busy loop, retry failure. > > > > I don't think this is problematic bahavior. Also, mlock can use asynchrounous lru drain. > > I think, more exactly, we don't have to drain lru pages for mlocking. > Mlocked pages will go into unevictable lru due to > try_to_unmap when shrink of lru happens. Right. > How about removing draining in case of mlock? Umm, I don't like this. because perfectly no drain often make strange test result. I mean /proc/meminfo::Mlock might be displayed unexpected value. it is not leak. it's only lazy cull. but many tester and administrator wiill think it's bug... ;) Practically, lru_add_drain_all() is nearly zero cost. because mlock's page fault is very costly operation. it hide drain cost. now, we only want to treat corner case issue. I don't hope dramatic change. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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