From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751164AbdCQPZZ (ORCPT ); Fri, 17 Mar 2017 11:25:25 -0400 Received: from gum.cmpxchg.org ([85.214.110.215]:40880 "EHLO gum.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751082AbdCQPZX (ORCPT ); Fri, 17 Mar 2017 11:25:23 -0400 Date: Fri, 17 Mar 2017 10:50:20 -0400 From: Johannes Weiner To: Yisheng Xie Cc: akpm@linux-foundation.org, mgorman@suse.de, vbabka@suse.cz, mhocko@suse.com, riel@redhat.com, shakeelb@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, guohanjun@huawei.com, qiuxishi@huawei.com Subject: Re: [PATCH v4] mm/vmscan: more restrictive condition for retry in do_try_to_free_pages Message-ID: <20170317145020.GA8106@cmpxchg.org> References: <1489577808-19228-1-git-send-email-xieyisheng1@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1489577808-19228-1-git-send-email-xieyisheng1@huawei.com> User-Agent: Mutt/1.8.0 (2017-02-23) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 15, 2017 at 07:36:48PM +0800, Yisheng Xie wrote: > By reviewing code, I find that when enter do_try_to_free_pages, the > may_thrash is always clear, and it will retry shrink zones to tap > cgroup's reserves memory by setting may_thrash when the former > shrink_zones reclaim nothing. > > However, when memcg is disabled or on legacy hierarchy, or there do not > have any memcg protected by low limit, it should not do this useless retry > at all, for we do not have any cgroup's reserves memory to tap, and we > have already done hard work but made no progress. > > To avoid this unneeded retrying, add a new field in scan_control named > memcg_low_protection, set it if there is any memcg protected by low limit > and only do the retry when memcg_low_protection is set while may_thrash > is clear. > > Signed-off-by: Yisheng Xie > Suggested-by: Michal Hocko > Suggested-by: Shakeel Butt > Reviewed-by: Shakeel Butt I don't see the point of this patch. It adds more code just to marginally optimize a near-OOM cold path. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f72.google.com (mail-wm0-f72.google.com [74.125.82.72]) by kanga.kvack.org (Postfix) with ESMTP id 1691F6B0038 for ; Fri, 17 Mar 2017 10:50:42 -0400 (EDT) Received: by mail-wm0-f72.google.com with SMTP id g8so4133218wmg.7 for ; Fri, 17 Mar 2017 07:50:42 -0700 (PDT) Received: from gum.cmpxchg.org (gum.cmpxchg.org. [85.214.110.215]) by mx.google.com with ESMTPS id u93si11438845wrb.292.2017.03.17.07.50.40 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 17 Mar 2017 07:50:40 -0700 (PDT) Date: Fri, 17 Mar 2017 10:50:20 -0400 From: Johannes Weiner Subject: Re: [PATCH v4] mm/vmscan: more restrictive condition for retry in do_try_to_free_pages Message-ID: <20170317145020.GA8106@cmpxchg.org> References: <1489577808-19228-1-git-send-email-xieyisheng1@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1489577808-19228-1-git-send-email-xieyisheng1@huawei.com> Sender: owner-linux-mm@kvack.org List-ID: To: Yisheng Xie Cc: akpm@linux-foundation.org, mgorman@suse.de, vbabka@suse.cz, mhocko@suse.com, riel@redhat.com, shakeelb@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, guohanjun@huawei.com, qiuxishi@huawei.com On Wed, Mar 15, 2017 at 07:36:48PM +0800, Yisheng Xie wrote: > By reviewing code, I find that when enter do_try_to_free_pages, the > may_thrash is always clear, and it will retry shrink zones to tap > cgroup's reserves memory by setting may_thrash when the former > shrink_zones reclaim nothing. > > However, when memcg is disabled or on legacy hierarchy, or there do not > have any memcg protected by low limit, it should not do this useless retry > at all, for we do not have any cgroup's reserves memory to tap, and we > have already done hard work but made no progress. > > To avoid this unneeded retrying, add a new field in scan_control named > memcg_low_protection, set it if there is any memcg protected by low limit > and only do the retry when memcg_low_protection is set while may_thrash > is clear. > > Signed-off-by: Yisheng Xie > Suggested-by: Michal Hocko > Suggested-by: Shakeel Butt > Reviewed-by: Shakeel Butt I don't see the point of this patch. It adds more code just to marginally optimize a near-OOM cold path. -- 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/ . Don't email: email@kvack.org