From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f200.google.com (mail-io0-f200.google.com [209.85.223.200]) by kanga.kvack.org (Postfix) with ESMTP id B1A836B0266 for ; Sun, 15 Jul 2018 01:26:07 -0400 (EDT) Received: by mail-io0-f200.google.com with SMTP id x5-v6so323818ioa.6 for ; Sat, 14 Jul 2018 22:26:07 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id k20-v6sor4666004ioh.58.2018.07.14.22.26.06 for (Google Transport Security); Sat, 14 Jul 2018 22:26:06 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <1531557122-12540-1-git-send-email-laoar.shao@gmail.com> From: Yafang Shao Date: Sun, 15 Jul 2018 13:25:25 +0800 Message-ID: Subject: Re: [PATCH] mm: avoid bothering interrupted task when charge memcg in softirq Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Shakeel Butt Cc: Johannes Weiner , Michal Hocko , Vladimir Davydov , Cgroups , Linux MM , LKML On Sun, Jul 15, 2018 at 12:25 PM, Shakeel Butt wrote: > On Sat, Jul 14, 2018 at 7:10 PM Yafang Shao wrote: >> >> On Sat, Jul 14, 2018 at 11:38 PM, Shakeel Butt wrote: >> > On Sat, Jul 14, 2018 at 1:32 AM Yafang Shao wrote: >> >> >> >> try_charge maybe executed in packet receive path, which is in interrupt >> >> context. >> >> In this situation, the 'current' is the interrupted task, which may has >> >> no relation to the rx softirq, So it is nonsense to use 'current'. >> >> >> > >> > Have you actually seen this occurring? >> >> Hi Shakeel, >> >> I'm trying to produce this issue, but haven't find it occur yet. >> >> > I am not very familiar with the >> > network code but I can think of two ways try_charge() can be called >> > from network code. Either through kmem charging or through >> > mem_cgroup_charge_skmem() and both locations correctly handle >> > interrupt context. >> > >> >> Why do you say that mem_cgroup_charge_skmem() correctly hanle >> interrupt context ? >> >> Let me show you why mem_cgroup_charge_skmem isn't hanling interrupt >> context correctly. >> >> mem_cgroup_charge_skmem() is calling try_charge() twice. >> The first one is with GFP_NOWAIT as the gfp_mask, and the second one >> is with (GFP_NOWAIT | __GFP_NOFAIL) as the gfp_mask. >> >> If page_counter_try_charge() failes at the first time, -ENOMEM is returned. >> Then mem_cgroup_charge_skmem() will call try_charge() once more with >> __GFP_NOFAIL set, and this time if If page_counter_try_charge() failes >> again the ' >> force' label in try_charge() will be executed and 0 is returned. >> >> No matter what, the 'current' will be used and touched, that is >> meaning mem_cgroup_charge_skmem() isn't hanling the interrupt context >> correctly. >> > > Hi Yafang, > > If you check mem_cgroup_charge_skmem(), the memcg passed is not > 'current' but is from the sock object i.e. sk->sk_memcg for which the > network buffer is allocated for. > That's correct, the memcg if from the sock object. But the point is, in this situation why 'current' is used in try_charge() ? As 'current' is not related with the memcg, which is just a interrupted task. > If the network buffers is allocated through kmem interface, the > charging is bypassed altogether (through memcg_kmem_bypass()) for > interrupt context. > Yes. Thanks Yafang