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Date: Wed, 9 Jan 2019 14:32:47 -0500
From: Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [RFC v3 PATCH 0/5] mm: memcontrol: do memory reclaim when
 offlining
Message-ID: <20190109193247.GA16319@cmpxchg.org>
References: <1547061285-100329-1-git-send-email-yang.shi@linux.alibaba.com>
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To: Yang Shi <yang.shi@linux.alibaba.com>
Cc: mhocko@suse.com, shakeelb@google.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org

On Thu, Jan 10, 2019 at 03:14:40AM +0800, Yang Shi wrote:
> 
> We have some usecases which create and remove memcgs very frequently,
> and the tasks in the memcg may just access the files which are unlikely
> accessed by anyone else.  So, we prefer force_empty the memcg before
> rmdir'ing it to reclaim the page cache so that they don't get
> accumulated to incur unnecessary memory pressure.  Since the memory
> pressure may incur direct reclaim to harm some latency sensitive
> applications.

We have kswapd for exactly this purpose. Can you lay out more details
on why that is not good enough, especially in conjunction with tuning
the watermark_scale_factor etc.?

We've been pretty adamant that users shouldn't use drop_caches for
performance for example, and that the need to do this usually is
indicative of a problem or suboptimal tuning in the VM subsystem.

How is this different?