linux-kernel - Re: [PATCH 2/3] mm,thp,shm: limit gfp mask to no more than specified

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Date:   Fri, 27 Nov 2020 14:03:39 -0500
From:   Rik van Riel <riel@...riel.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     hughd@...gle.com, xuyu@...ux.alibaba.com,
        akpm@...ux-foundation.org, mgorman@...e.de, aarcange@...hat.com,
        willy@...radead.org, linux-kernel@...r.kernel.org,
        kernel-team@...com, linux-mm@...ck.org, vbabka@...e.cz
Subject: Re: [PATCH 2/3] mm,thp,shm: limit gfp mask to no more than specified

On Fri, 2020-11-27 at 08:52 +0100, Michal Hocko wrote:
> On Thu 26-11-20 13:04:14, Rik van Riel wrote:
> > 
> > I would be more than happy to implement things differently,
> > but I am not sure what alternative you are suggesting.
> 
> Simply do not alter gfp flags? Or warn in some cases of a serious
> mismatch.
> E.g. GFP_ZONEMASK mismatch because there are already GFP_KERNEL users
> of
> shmem.

Not altering the gfp flags is not really an option,
because that would leads to attempting to allocate THPs
with GFP_HIGHUSER, which is what is used to allocate
regular tmpfs pages.

If the THP configuration in sysfs says we should
not
be doing compaction/reclaim from THP allocations, we
should obey that configuration setting, and use a 
gfp_flags that results in no compaction/reclaim being done.

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