Messages in this thread | | | Date | Thu, 10 Sep 2009 10:23:41 +0900 | From | Minchan Kim <> | Subject | Re: [rfc] lru_add_drain_all() vs isolation |
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On Thu, 10 Sep 2009 10:15:07 +0900 (JST) KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
> > On Thu, 10 Sep 2009 08:58:20 +0900 (JST) > > KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote: > > > > > > On Wed, Sep 9, 2009 at 1:27 PM, KOSAKI Motohiro > > > > <kosaki.motohiro@jp.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... ;) > > > > I agree. I have no objection to your approach. :) > > > > > 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. > > > > Another problem is as follow. > > > > Although some CPUs don't have any thing to do, we do it. > > HPC guys don't want to consume CPU cycle as Christoph pointed out. > > I liked Peter's idea with regard to this. > > My approach can solve it, too. > > But I agree it would be dramatic change. > > Is Perter's + mine approach bad?
It's good to me! :)
> It mean, > > - RT-thread binding cpu is not grabbing the page > -> mlock successful by Peter's improvement > - RT-thread binding cpu is grabbing the page > -> mlock successful by mine approach > the page is culled later. > > > >
-- 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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