linux-kernel - Re: [PATCH] dm ioctl: Restore __GFP_HIGH in copy

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Message-ID: <20170519074647.GC13041@dhcp22.suse.cz>
Date:   Fri, 19 May 2017 09:46:47 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Junaid Shahid <junaids@...gle.com>
Cc:     David Rientjes <rientjes@...gle.com>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        andreslc@...gle.com, gthelen@...gle.com, mpatocka@...hat.com,
        vbabka@...e.cz, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dm ioctl: Restore __GFP_HIGH in copy_params()

On Thu 18-05-17 19:50:46, Junaid Shahid wrote:
> (Adding back the correct linux-mm email address and also adding linux-kernel.)
> 
> On Thursday, May 18, 2017 01:41:33 PM David Rientjes wrote:
[...]
> > Let's ask Mikulas, who changed this from PF_MEMALLOC to __GFP_HIGH, 
> > assuming there was a reason to do it in the first place in two different 
> > ways.

Hmm, the old PF_MEMALLOC used to have the following comment
        /*
         * Trying to avoid low memory issues when a device is
         * suspended. 
         */

I am not really sure what that means but __GFP_HIGH certainly have a
different semantic than PF_MEMALLOC. The later grants the full access to
the memory reserves while the prior on partial access. If this is _really_
needed then it deserves a comment explaining why.
-- 
Michal Hocko
SUSE Labs