From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chris Down <chris@chrisdown.name>
Subject: Re: [RFC PATCH 0/8] memcg: Enable fine-grained per process memory
 control
Date: Mon, 7 Sep 2020 12:47:45 +0100
Message-ID: <20200907114745.GA1076657@chrisdown.name>
References: <20200817140831.30260-1-longman@redhat.com>
 <20200818091453.GL2674@hirez.programming.kicks-ass.net>
 <20200818092617.GN28270@dhcp22.suse.cz>
 <20200818095910.GM2674@hirez.programming.kicks-ass.net>
 <20200818100516.GO28270@dhcp22.suse.cz>
 <20200818101844.GO2674@hirez.programming.kicks-ass.net>
 <20200818134900.GA829964@cmpxchg.org>
 <20200821193716.GU3982@worktop.programming.kicks-ass.net>
 <20200824165850.GA932571@cmpxchg.org>
Mime-Version: 1.0
Return-path: <linux-fsdevel-owner@vger.kernel.org>
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
        d=chrisdown.name; s=google;
        h=date:from:to:cc:subject:message-id:references:mime-version
         :content-disposition:in-reply-to:user-agent;
        bh=395Y0lUxtoxk+N6Xwo36+dBOIhVjSE/2+oZvPClU7KM=;
        b=cuAJnS9cKwag10JrR5XWKLTSDpsVij2RIxygdpxgcJAAdzqC0pGMP0broEdFrjuV2u
         YK1YpzjfS7JWBVBZPRmTUcfnAukLTXmsLJ2XSzMOmdbEBvGaIW/6SMoesJ2yxCpA/WG2
         m8QnLvvHNNu3zgtJUbsMfzQakaNE4sxXw5yG0=
Content-Disposition: inline
In-Reply-To: <20200824165850.GA932571@cmpxchg.org>
Sender: linux-fsdevel-owner@vger.kernel.org
List-ID: <cgroups.vger.kernel.org>
Content-Type: text/plain; charset="us-ascii"; format="flowed"
Content-Transfer-Encoding: 7bit
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Peter Zijlstra <peterz@infradead.org>, Michal Hocko <mhocko@suse.com>, Waiman Long <longman@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, Vladimir Davydov <vdavydov.dev@gmail.com>, Jonathan Corbet <corbet@lwn.net>, Alexey Dobriyan <adobriyan@gmail.com>, Ingo Molnar <mingo@kernel.org>, Juri Lelli <juri.lelli@redhat.com>, Vincent Guittot <vincent.guittot@linaro.org>, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org

Johannes Weiner writes:
>That all being said, the semantics of the new 'high' limit in cgroup2
>have allowed us to move reclaim/limit enforcement out of the
>allocation context and into the userspace return path.
>
>See the call to mem_cgroup_handle_over_high() from
>tracehook_notify_resume(), and the comments in try_charge() around
>set_notify_resume().
>
>This already solves the free->alloc ordering problem by allowing the
>allocation to exceed the limit temporarily until at least all locks
>are dropped, we know we can sleep etc., before performing enforcement.
>
>That means we may not need the timed sleeps anymore for that purpose,
>and could bring back directed waits for freeing-events again.
>
>What do you think? Any hazards around indefinite sleeps in that resume
>path? It's called before __rseq_handle_notify_resume and the
>arch-specific resume callback (which appears to be a no-op currently).
>
>Chris, Michal, what are your thoughts? It would certainly be simpler
>conceptually on the memcg side.

I'm not against that, although I personally don't feel very strongly about it 
either way, since the current behaviour clearly works in practice.