linux-kernel - Re: Pinning ZONE

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Date:   Tue, 24 Nov 2020 09:43:50 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     Vlastimil Babka <vbabka@...e.cz>, linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Sasha Levin <sashal@...nel.org>,
        Tyler Hicks <tyhicks@...ux.microsoft.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, sthemmin@...rosoft.com,
        John Hubbard <jhubbard@...dia.com>
Subject: Re: Pinning ZONE_MOVABLE pages

On Mon 23-11-20 11:31:59, Pavel Tatashin wrote:
[...]
> Also, we still need to take care of the fault scenario.

Forgot to reply to this part. I believe you mean this to be fault at gup
time, right? Then the easiest way forward would be to either add yet
another scoped flag or (maybe) better to generalize memalloc_nocma_* to
imply that the allocated memory is going to be unmovable so drop
__GFP_MOVABLE and also forbid CMA. I have to admit that I do not
remember why long term pin on CMA pages is ok to go to movable but I
strongly suspect this is just shifting problem around.
-- 
Michal Hocko
SUSE Labs