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Tue, 29 Mar 2022 17:47:50 -0700 (PDT) Date: Wed, 30 Mar 2022 00:47:50 +0000 From: Wei Yang To: Johannes Weiner Cc: Wei Yang , mhocko@kernel.org, vdavydov.dev@gmail.com, akpm@linux-foundation.org, cgroups@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 2/3] mm/memcg: set pos to prev unconditionally Message-ID: <20220330004750.fx4jr4bnehz4ynpf@master> Reply-To: Wei Yang References: <20220225003437.12620-1-richard.weiyang@gmail.com> <20220225003437.12620-3-richard.weiyang@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: m6qd5p8xmr6rcaza6xyo1nm9qk734efz Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=kX4HPdde; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf21.hostedemail.com: domain of richard.weiyang@gmail.com designates 209.85.218.44 as permitted sender) smtp.mailfrom=richard.weiyang@gmail.com X-Rspamd-Queue-Id: C2F171C000A X-HE-Tag: 1648601272-371381 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Mar 29, 2022 at 02:48:05PM -0400, Johannes Weiner wrote: >On Fri, Feb 25, 2022 at 12:34:36AM +0000, Wei Yang wrote: >> Current code set pos to prev based on condition (prev && !reclaim), >> while we can do this unconditionally. >> >> Since: >> >> * If !reclaim, pos is the same as prev no matter it is NULL or not. >> * If reclaim, pos would be set properly from iter->position. >> >> Signed-off-by: Wei Yang >> --- >> mm/memcontrol.c | 5 +---- >> 1 file changed, 1 insertion(+), 4 deletions(-) >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index 9464fe2aa329..03399146168f 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -980,7 +980,7 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root, >> struct mem_cgroup_reclaim_iter *iter; >> struct cgroup_subsys_state *css = NULL; >> struct mem_cgroup *memcg = NULL; >> - struct mem_cgroup *pos = NULL; >> + struct mem_cgroup *pos = prev; > >I don't like this so much. It suggests pos always starts with prev, no >matter what. But this isn't true for reclaim mode, which overrides the >initialized value again. > >> if (mem_cgroup_disabled()) >> return NULL; >> @@ -988,9 +988,6 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root, >> if (!root) >> root = root_mem_cgroup; >> >> - if (prev && !reclaim) >> - pos = prev; > >How about making the reclaim vs non-reclaim mode explicit and do: > > if (reclaim) { > ... > pos = iter->position; > ... > } else { > pos = prev; > } Something like this? diff --git a/mm/memcontrol.c b/mm/memcontrol.c index eed9916cdce5..5d433b79ba47 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1005,9 +1005,6 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root, if (!root) root = root_mem_cgroup; - if (prev && !reclaim) - pos = prev; - rcu_read_lock(); if (reclaim) { @@ -1033,6 +1030,8 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root, */ (void)cmpxchg(&iter->position, pos, NULL); } + } else if (prev) { + pos = prev; } if (pos) -- Wei Yang Help you, Help me