From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [PATCH v2] mm: memcontrol: remove obsolete comment of mem_cgroup_unmark_under_oom() Date: Wed, 30 Sep 2020 10:43:43 +0200 Message-ID: <20200930084343.GO2277@dhcp22.suse.cz> References: <7d1ea112d8a740cab555eaf7be530286@huawei.com> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1601455424; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=QhiptoBURkg4uq4dMDHGe+8biN2SOcQktd4lq8iMzC4=; b=VfV4dAj7zRnkAOtH9oe2lFoD+GI1LiJPXeQl9iW87xGUeS7/HL4Tf4zh4DG4lZqyanotic qxviOA9fNLmmfV8/5czDMQKDRRwCGC00zf4qsG5MwCLidLYExCBcKV5pKVfCRjRESXR7iK CkDeAVlzxX3OD7eMMZSQ3noEWtrfLEE= Content-Disposition: inline In-Reply-To: <7d1ea112d8a740cab555eaf7be530286@huawei.com> List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linmiaohe Cc: "hannes@cmpxchg.org" , "vdavydov.dev@gmail.com" , "akpm@linux-foundation.org" , "cgroups@vger.kernel.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" On Wed 30-09-20 01:34:25, linmiaohe wrote: > Michal Hocko wrote: > > On Thu 17-09-20 06:59:00, Miaohe Lin wrote: > >> Since commit 79dfdaccd1d5 ("memcg: make oom_lock 0 and 1 based rather > >> than counter"), the mem_cgroup_unmark_under_oom() is added and the > >> comment of the mem_cgroup_oom_unlock() is moved here. But this comment > >> make no sense here because mem_cgroup_oom_lock() does not operate on under_oom field. > > > >OK, so I've looked into this more deeply and I finally remember why we have this comment here. The point is that under_oom shouldn't underflow and that we have to explicitly check for > 0 because a new child memcg could have been added between mem_cgroup_mark_under_oom and mem_cgroup_unmark_under_oom. > > > >So the comment makes sense although it is not as helpful as it could be. > >I think that changing it to the following will be more usefule > > > > /* > > * Be careful about under_oom underflows becase a child memcg > > * could have neem added after mem_cgroup_mark_under_oom > > Should it be s/neem/been/ ? yep, fat fingers... > > > */ > > Many thanks for detailed explanation. Will fix it in v2. Thanks again. -- Michal Hocko SUSE Labs