linux-kernel - Re: [RFC] [PATCH 0/8] Migrate Pages in lieu of discard

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Message-ID: <9c47b66b-f381-4b98-2e8f-7262e8567e15@intel.com>
Date:   Wed, 1 Jul 2020 07:32:16 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Zi Yan <ziy@...dia.com>
Cc:     Shakeel Butt <shakeelb@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        David Rientjes <rientjes@...gle.com>,
        Huang Ying <ying.huang@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [RFC] [PATCH 0/8] Migrate Pages in lieu of discard

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On 7/1/20 7:24 AM, Zi Yan wrote:
> On 30 Jun 2020, at 15:31, Dave Hansen wrote:
>>> BTW is this proposal only for systems having multi-tiers of
>>> memory? Can a multi-node DRAM-only system take advantage of
>>> this proposal? For example I have a system with two DRAM nodes
>>> running two jobs hardwalled to each node. For each job the
>>> other node is kind of low-tier memory. If I can describe the
>>> per-job demotion paths then these jobs can take advantage of
>>> this proposal during occasional peaks.
>> I don't see any reason it could not work there.  There would just
>> need to be a way to set up a different demotion path policy that
>> what was done here.
> We might need a different threshold (or GFP flag) for allocating
> new pages in remote node for demotion. Otherwise, we could see
> scenarios like: two nodes in a system are almost full and Node A
> is trying to demote some pages to Node B, which triggers page
> demotion from Node B to Node A.

I've always assumed that migration cycles would be illegal since it's
so hard to guarantee forward reclaim progress with them in place.
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