linux-kernel - Re: [PATCH 00/10] [v6] Migrate Pages in lieu of discard

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Date:   Tue, 9 Mar 2021 13:52:42 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Yang Shi <shy828301@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     Linux Kernel Mailing List <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>,
        David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH 00/10] [v6] Migrate Pages in lieu of discard

...
>> == Open Issues ==
>>
>>  * For cpusets and memory policies that restrict allocations
>>    to PMEM, is it OK to demote to PMEM?  Do we need a cgroup-
>>    level API to opt-in or opt-out of these migrations?
> 
> I'm wondering if such usecases, which don't want to have memory
> allocate on pmem, will allow memory swapped out or reclaimed? If swap
> is allowed then I failed to see why migrating to pmem should be
> disallowed. If swap is not allowed, they should call mlock, then the
> memory won't be migrated to pmem as well.

Agreed.  I have a hard time imagining there are a lot of folks that can
tolerate the massive overhead from swapping, but can't tolerate the much
smaller overhead of going to pmem instead of DRAM.