linux-kernel - Re: [PATCH 01/19] tree wide: get rid of __GFP

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Message-ID: <alpine.DEB.2.10.1604141255020.6593@chino.kir.corp.google.com>
Date:	Thu, 14 Apr 2016 12:56:28 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Michal Hocko <mhocko@...nel.org>
cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.com>, linux-arch@...r.kernel.org
Subject: Re: [PATCH 01/19] tree wide: get rid of __GFP_REPEAT for order-0
 allocations part I

On Mon, 11 Apr 2016, 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. Yet we have
> the full kernel tree with its usage for apparently order-0 allocations.
> This is really confusing because __GFP_REPEAT is explicitly documented
> to allow allocation failures which is a weaker semantic than the current
> order-0 has (basically nofail).
> 
> Let's simply drop __GFP_REPEAT from those places. This would allow
> to identify place which really need allocator to retry harder and
> formulate a more specific semantic for what the flag is supposed to do
> actually.
> 
> Cc: linux-arch@...r.kernel.org
> Signed-off-by: Michal Hocko <mhocko@...e.com>

I did exactly this before, and Andrew objected saying that __GFP_REPEAT 
may not be needed for the current page allocator's implementation but 
could with others and that setting __GFP_REPEAT for an allocation 
provided useful information with regards to intent.  At the time, I 
attempted to eliminate __GFP_REPEAT entirely.