Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754472Ab1FWGQQ (ORCPT ); Thu, 23 Jun 2011 02:16:16 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:40335 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753066Ab1FWGQP (ORCPT ); Thu, 23 Jun 2011 02:16:15 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Date: Thu, 23 Jun 2011 15:08:42 +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: [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: <20110623150842.d13492cd.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20110622123204.GC14343@tiehlicka.suse.cz> References: <20110622120635.GB14343@tiehlicka.suse.cz> <20110622121516.GA28359@infradead.org> <20110622123204.GC14343@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: 5302 Lines: 159 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 ? 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 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; + } put_page(dirty_page); if (page_mkwrite && mapping) { /* @@ -3282,6 +3287,11 @@ out: file_update_time(vma->vm_file); } else { unlock_page(vmf.page); + if (need_charge) { + if (mem_cgroup_newpage_charge(need_charge, + mm, GFP_KERNEL)) + ret = VM_FAULT_OOM; + } if (anon) page_cache_release(vmf.page); } -- 1.7.4.1 -- 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/