From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with ESMTP id 62B85900194 for ; Thu, 23 Jun 2011 09:51:31 -0400 (EDT) Received: by bwz17 with SMTP id 17so2314262bwz.14 for ; Thu, 23 Jun 2011 06:51:28 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20110623132312.GI31593@tiehlicka.suse.cz> References: <20110622120635.GB14343@tiehlicka.suse.cz> <20110622121516.GA28359@infradead.org> <20110622123204.GC14343@tiehlicka.suse.cz> <20110623150842.d13492cd.kamezawa.hiroyu@jp.fujitsu.com> <20110623074133.GA31593@tiehlicka.suse.cz> <20110623170811.16f4435f.kamezawa.hiroyu@jp.fujitsu.com> <20110623090204.GE31593@tiehlicka.suse.cz> <20110623190157.1bc8cbb9.kamezawa.hiroyu@jp.fujitsu.com> <20110623115855.GF31593@tiehlicka.suse.cz> <20110623132312.GI31593@tiehlicka.suse.cz> Date: Thu, 23 Jun 2011 22:51:28 +0900 Message-ID: Subject: Re: [PATCH] mm: preallocate page before lock_page at filemap COW. (WasRe: [PATCH V2] mm: Do not keep page locked during page fault while charging it for memcg From: Hiroyuki Kamezawa Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: KAMEZAWA Hiroyuki , Christoph Hellwig , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Hugh Dickins , Rik van Riel , Michel Lespinasse , Mel Gorman , Lutz Vieweg 2011/6/23 Michal Hocko : > On Thu 23-06-11 22:01:40, Hiroyuki Kamezawa wrote: >> 2011/6/23 Michal Hocko : >> > On Thu 23-06-11 19:01:57, KAMEZAWA Hiroyuki wrote: >> >> On Thu, 23 Jun 2011 11:02:04 +0200 >> >> Michal Hocko wrote: >> >> >> >> > On Thu 23-06-11 17:08:11, KAMEZAWA Hiroyuki wrote: >> >> > > On Thu, 23 Jun 2011 09:41:33 +0200 >> >> > > Michal Hocko wrote: >> >> > [...] >> >> > > > Other than that: >> >> > > > Reviewed-by: Michal Hocko >> >> > > > >> >> > > >> >> > > I found the page is added to LRU before charging. (In this case, >> >> > > memcg's LRU is ignored.) I'll post a new version with a fix. >> >> > >> >> > Yes, you are right. I have missed that. >> >> > This means that we might race with reclaim which could evict the COWed >> >> > page wich in turn would uncharge that page even though we haven't >> >> > charged it yet. >> >> > >> >> > Can we postpone page_add_new_anon_rmap to the charging path or it would >> >> > just race somewhere else? >> >> > >> >> >> >> I got a different idea. How about this ? >> >> I think this will have benefit for non-memcg users under OOM, too. >> > >> > Could you be more specific? I do not see how preallocation which might >> > turn out to be pointless could help under OOM. >> > >> >> We'll have no page allocation under lock_page() held in this path. >> I think it is good. > > But it can also cause that the page, we are about to fault in, is evicted > due to allocation so we would have to do a major fault... This is > probably not that serious, though. For other purpose, I have(had) other patch to prevent it (and planned to post it.) The basic logic is... 1. add a new member variable to vm_area_struct as vma->vm_faulting_to 2. at __do_fault(), set vm_faulting_to as vma->vm_faulting_to = pgoff. 3. chec vma->vm_faulting_to at page_referenced_file() as if (pgoff (Was page->index) == vma->vm_faulting_to) referenced++ Then, the page which someone is waiting for page-fault will be marked as referenced and go KEEP_LOCKED. (vm_faulting_to can be cleared after we got lock_page()). In corner case, several threads which shares vma may fault into a vma. But this will help typical case and have no overheads, I think. Thanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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: email@kvack.org