linux-kernel - Re: [PATCH 04/17] arm: get rid of superfluous __GFP

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Message-ID: <20160601162424.GD19428@n2100.arm.linux.org.uk>
Date:	Wed, 1 Jun 2016 17:24:24 +0100
From:	Russell King - ARM Linux <linux@...linux.org.uk>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.com>, linux-arch@...r.kernel.org
Subject: Re: [PATCH 04/17] arm: get rid of superfluous __GFP_REPEAT

On Mon, May 30, 2016 at 11:14:46AM +0200, Michal Hocko wrote:
> From: Michal Hocko <mhocko@...e.com>
> 
> __GFP_REPEAT has a rather weak semantic but since it has been introduced
> around 2.6.12 it has been ignored for low order allocations.
> 
> PGALLOC_GFP uses __GFP_REPEAT but none of the allocation which uses
> this flag is for more than order-2. This means that this flag has never
> been actually useful here because it has always been used only for
> PAGE_ALLOC_COSTLY requests.

I hear what you say, but...

commit 8c65da6dc89ccb605d73773b1dd617e72982d971
Author: Russell King <rmk+kernel@....linux.org.uk>
Date:   Sat Nov 30 12:52:31 2013 +0000

    ARM: pgd allocation: retry on failure

    Make pgd allocation retry on failure; we really need this to succeed
    otherwise fork() can trigger OOMs.

    Signed-off-by: Russell King <rmk+kernel@....linux.org.uk>

and that's the change which introduced this, and it did solve a problem
for me.  So I'm not happy to give an ack for this change unless someone
can tell me why adding __GFP_REPEAT back then had a beneficial effect.
Maybe there was some other bug in the MM layer in 2013 which this change
happened to solve?

-- 
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