Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758238Ab1FWIPi (ORCPT ); Thu, 23 Jun 2011 04:15:38 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:34403 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753667Ab1FWIPf (ORCPT ); Thu, 23 Jun 2011 04:15:35 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Date: Thu, 23 Jun 2011 17:08:11 +0900 From: KAMEZAWA Hiroyuki To: Michal Hocko Cc: Christoph Hellwig , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Hugh Dickins , Rik van Riel , Michel Lespinasse , Mel Gorman , Lutz Vieweg Subject: Re: [PATCH] memcg: unlock page before charging it. (WasRe: [PATCH V2] mm: Do not keep page locked during page fault while charging it for memcg Message-Id: <20110623170811.16f4435f.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20110623074133.GA31593@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> Organization: FUJITSU Co. LTD. X-Mailer: Sylpheed 3.1.1 (GTK+ 2.10.14; i686-pc-mingw32) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6132 Lines: 171 On Thu, 23 Jun 2011 09:41:33 +0200 Michal Hocko wrote: > On Thu 23-06-11 15:08:42, KAMEZAWA Hiroyuki wrote: > > On Wed, 22 Jun 2011 14:32:04 +0200 > > Michal Hocko wrote: > > > > > On Wed 22-06-11 08:15:16, Christoph Hellwig wrote: > > > > > + > > > > > + /* We have to drop the page lock here because memcg > > > > > + * charging might block for unbound time if memcg oom > > > > > + * killer is disabled. > > > > > + */ > > > > > + unlock_page(vmf.page); > > > > > + ret = mem_cgroup_newpage_charge(page, mm, GFP_KERNEL); > > > > > + lock_page(vmf.page); > > > > > > > > This introduces a completely poinless unlock/lock cycle for non-memcg > > > > pagefaults. Please make sure it only happens when actually needed. > > > > > > Fair point. Thanks! > > > What about the following? > > > I realize that pushing more memcg logic into mm/memory.c is not nice but > > > I found it better than pushing the old page into mem_cgroup_newpage_charge. > > > We could also check whether the old page is in the root cgroup because > > > memcg oom killer is not active there but that would add more code into > > > this hot path so I guess it is not worth it. > > > > > > Changes since v1 > > > - do not unlock page when memory controller is disabled. > > > > > > > Great work. Then I confirmed Lutz' problem is fixed. > > > > But I like following style rather than additional lock/unlock. > > How do you think ? > > Yes, I like it much more than the hairy way I did it. See comments bellow. > > > I tested this on the latest git tree and confirmed > > the Lutz's livelock problem is fixed. And I think this should go stable tree. > > > > > > == > > From 7e9250da9ff529958d4c1ff511458dbdac8e4b81 Mon Sep 17 00:00:00 2001 > > From: KAMEZAWA Hiroyuki > > Date: Thu, 23 Jun 2011 15:05:57 +0900 > > Subject: [PATCH] memcg: unlock page before charging it. > > > > Currently we are keeping faulted page locked throughout whole __do_fault > > call (except for page_mkwrite code path). If we do early COW we allocate a > > new page which has to be charged for a memcg (mem_cgroup_newpage_charge). > > > > This function, however, might block for unbounded amount of time if memcg > > oom killer is disabled or fork-bomb is running because the only way out of > > the OOM situation is either an external event or OOM-situation fix. > > > > processes from faulting it in which is not good at all because we are > > Missing the beginning of the sentence? > Ah, yes... > > basically punishing potentially an unrelated process for OOM condition > > in a different group (I have seen stuck system because of ld-2.11.1.so being > > locked). > > > > We can do test easily. > > % cgcreate -g memory:A > > % cgset -r memory.limit_in_bytes=64M A > > % cgset -r memory.memsw.limit_in_bytes=64M A > > % cd kernel_dir; cgexec -g memory:A make -j > > > > Then, the whole system will live-locked until you kill 'make -j' > > by hands (or push reboot...) This is because some important > > page in a shared library are locked and never released bcause of fork-bomb. > > > > This patch delays "charge" until unlock_page() called. There is > > no problem as far as we keep reference on a page. > > (memcg doesn't require page_lock()). > > > > Then, above livelock disappears. > > > > Reported-by: Lutz Vieweg > > Original-idea-by: Michal Hocko > > Signed-off-by: KAMEZAWA Hiroyuki > > --- > > mm/memory.c | 28 +++++++++++++++++++--------- > > 1 files changed, 19 insertions(+), 9 deletions(-) > > > > diff --git a/mm/memory.c b/mm/memory.c > > index 87d9353..66442da 100644 > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -3129,7 +3129,7 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma, > > struct page *page; > > pte_t entry; > > int anon = 0; > > - int charged = 0; > > + struct page *need_charge = NULL; > > struct page *dirty_page = NULL; > > struct vm_fault vmf; > > int ret; > > @@ -3177,12 +3177,7 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma, > > ret = VM_FAULT_OOM; > > goto out; > > } > > - if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL)) { > > - ret = VM_FAULT_OOM; > > - page_cache_release(page); > > - goto out; > > - } > > - charged = 1; > > + need_charge = page; > > copy_user_highpage(page, vmf.page, address, vma); > > __SetPageUptodate(page); > > } else { > > @@ -3251,12 +3246,11 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma, > > /* no need to invalidate: a not-present page won't be cached */ > > update_mmu_cache(vma, address, page_table); > > } else { > > - if (charged) > > - mem_cgroup_uncharge_page(page); > > if (anon) > > page_cache_release(page); > > else > > anon = 1; /* no anon but release faulted_page */ > > + need_charge = NULL; > > } > > > > pte_unmap_unlock(page_table, ptl); > > @@ -3268,6 +3262,17 @@ out: > > if (set_page_dirty(dirty_page)) > > page_mkwrite = 1; > > unlock_page(dirty_page); > > + if (need_charge) { > > + /* > > + * charge this page before we drop refcnt. > > + * memory cgroup returns OOM condition when > > + * this task is killed. So, it's not necesasry > > + * to undo. > > + */ > > + if (mem_cgroup_newpage_charge(need_charge, > > + mm, GFP_KERNEL)) > > + ret = VM_FAULT_OOM; > > + } > > We do not need this hunk, don't we? dirty_page is set only if !anon so > we never get to this path from COW. > You're right. (And Nishimura pointed out this, too) > 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. Thanks, -Kame -- 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/