From: Andrew Morton <akpm@linux-foundation.org>
To: Mina Almasry <almasrymina@google.com>
Cc: Huang Ying <ying.huang@intel.com>,
Yang Shi <yang.shi@linux.alibaba.com>,
Yosry Ahmed <yosryahmed@google.com>,
Tim Chen <tim.c.chen@linux.intel.com>,
weixugc@google.com, shakeelb@google.com, gthelen@google.com,
fvdl@google.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1] mm: disable top-tier fallback to reclaim on proactive reclaim
Date: Fri, 2 Dec 2022 13:38:40 -0800 [thread overview]
Message-ID: <20221202133840.5cdd4270cf73eaaa1d9d0345@linux-foundation.org> (raw)
In-Reply-To: <20221201233317.1394958-1-almasrymina@google.com>
On Thu, 1 Dec 2022 15:33:17 -0800 Mina Almasry <almasrymina@google.com> wrote:
> Reclaiming directly from top tier nodes breaks the aging pipeline of
> memory tiers. If we have a RAM -> CXL -> storage hierarchy, we
> should demote from RAM to CXL and from CXL to storage. If we reclaim
> a page from RAM, it means we 'demote' it directly from RAM to storage,
> bypassing potentially a huge amount of pages colder than it in CXL.
>
> However disabling reclaim from top tier nodes entirely would cause ooms
> in edge scenarios where lower tier memory is unreclaimable for whatever
> reason, e.g. memory being mlocked() or too hot to reclaim. In these
> cases we would rather the job run with a performance regression rather
> than it oom altogether.
>
> However, we can disable reclaim from top tier nodes for proactive reclaim.
> That reclaim is not real memory pressure, and we don't have any cause to
> be breaking the aging pipeline.
>
Is this purely from code inspection, or are there quantitative
observations to be shared?
next prev parent reply other threads:[~2022-12-02 21:38 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-01 23:33 Mina Almasry
2022-12-02 2:44 ` Huang, Ying
2022-12-02 21:38 ` Andrew Morton [this message]
2022-12-02 21:52 ` Mina Almasry
2022-12-05 23:37 ` Yang Shi
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