From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754451AbcBGS6K (ORCPT ); Sun, 7 Feb 2016 13:58:10 -0500 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:61012 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753902AbcBGS6H convert rfc822-to-8bit (ORCPT ); Sun, 7 Feb 2016 13:58:07 -0500 From: Johannes Weiner To: Vladimir Davydov CC: Johannes Weiner , Andrew Morton , Hugh Dickins , Michal Hocko , Mateusz Guzik , Sergey Senozhatsky , "linux-mm@kvack.org" , "cgroups@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Kernel Team Subject: Re: [PATCH 2/2] mm: memcontrol: drop unnecessary lru locking from mem_cgroup_migrate() Thread-Topic: [PATCH 2/2] mm: memcontrol: drop unnecessary lru locking from mem_cgroup_migrate() Thread-Index: AQHRX4fcnHd+9wIsvE6tfFp/GrOS6Z8hdToA//9+llw= Date: Sun, 7 Feb 2016 18:57:49 +0000 Message-ID: <28CC6A8F-E642-4DF5-A8E5-DB9BB62DA429@fb.com> References: <1454616467-8994-1-git-send-email-hannes@cmpxchg.org> <1454616467-8994-2-git-send-email-hannes@cmpxchg.org>,<20160207184059.GB19151@esperanza> In-Reply-To: <20160207184059.GB19151@esperanza> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-Proofpoint-Spam-Reason: safe X-FB-Internal: Safe X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-02-07_10:,, signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Feb 7, 2016, at 1:41 PM, Vladimir Davydov wrote: > >> On Thu, Feb 04, 2016 at 03:07:47PM -0500, Johannes Weiner wrote: >> Migration accounting in the memory controller used to have to handle >> both oldpage and newpage being on the LRU already; fuse's page cache >> replacement used to pass a recycled newpage that had been uncharged >> but not freed and removed from the LRU, and the memcg migration code >> used to uncharge oldpage to "pass on" the existing charge to newpage. >> >> Nowadays, pages are no longer uncharged when truncated from the page >> cache, but rather only at free time, so if a LRU page is recycled in >> page cache replacement it'll also still be charged. And we bail out of >> the charge transfer altogether in that case. Tell commit_charge() that >> we know newpage is not on the LRU, to avoid taking the zone->lru_lock >> unnecessarily from the migration path. >> >> But also, oldpage is no longer uncharged inside migration. We only use >> oldpage for its page->mem_cgroup and page size, so we don't care about >> its LRU state anymore either. Remove any mention from the kernel doc. >> >> Signed-off-by: Johannes Weiner >> Suggested-by: Hugh Dickins > > Acked-by: Vladimir Davydov Thanks! > @@ -5483,6 +5483,7 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage) > unsigned int nr_pages; > bool compound; > > + VM_BUG_ON_PAGE(PageLRU(newpage), newpage); That's actually possible for fuse. But in that case newpage is charged and we bail.