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Date: Thu, 30 Nov 2023 13:33:40 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Dan Schatzberg <schatzberg.dan@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>, Roman Gushchin
 <roman.gushchin@linux.dev>, Yosry Ahmed <yosryahmed@google.com>, Huan Yang
 <link@vivo.com>, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
 linux-mm@kvack.org, Michal Hocko <mhocko@kernel.org>, Shakeel Butt
 <shakeelb@google.com>, Muchun Song <muchun.song@linux.dev>, David
 Hildenbrand <david@redhat.com>, Matthew Wilcox <willy@infradead.org>, Huang
 Ying <ying.huang@intel.com>, Kefeng Wang <wangkefeng.wang@huawei.com>,
 Peter Xu <peterx@redhat.com>, "Vishal Moola (Oracle)"
 <vishal.moola@gmail.com>, Yue Zhao <findns94@gmail.com>, Hugh Dickins
 <hughd@google.com>
Subject: Re: [PATCH 1/1] mm: add swapiness= arg to memory.reclaim
Message-Id: <20231130133340.36140526608289898acb3ac5@linux-foundation.org>
In-Reply-To: <20231130153658.527556-2-schatzberg.dan@gmail.com>
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	<20231130153658.527556-2-schatzberg.dan@gmail.com>
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On Thu, 30 Nov 2023 07:36:54 -0800 Dan Schatzberg <schatzberg.dan@gmail.com> wrote:

> Allow proactive reclaimers to submit an additional swappiness=<val>
> argument to memory.reclaim. This overrides the global or per-memcg
> swappiness setting for that reclaim attempt.
> 
> For example:
> 
> echo "2M swappiness=0" > /sys/fs/cgroup/memory.reclaim
> 
> will perform reclaim on the rootcg with a swappiness setting of 0 (no
> swap) regardless of the vm.swappiness sysctl setting.
> 
> Signed-off-by: Dan Schatzberg <schatzberg.dan@gmail.com>
> ---
>  include/linux/swap.h |  3 ++-
>  mm/memcontrol.c      | 55 +++++++++++++++++++++++++++++++++++---------
>  mm/vmscan.c          | 13 +++++++++--

Documentation/admin-guide/cgroup-v2.rst is feeling unloved!

Please check whether this interface change can lead to
non-backward-compatible userspace.  If someone's script does the above
echo command, will it break on older kernels?  If so, does it matter?