Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752248AbcDOHo2 (ORCPT ); Fri, 15 Apr 2016 03:44:28 -0400 Received: from mail-pf0-f194.google.com ([209.85.192.194]:36466 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751517AbcDOHoZ (ORCPT ); Fri, 15 Apr 2016 03:44:25 -0400 Date: Fri, 15 Apr 2016 09:44:21 +0200 From: Michal Hocko To: David Rientjes Cc: linux-mm@kvack.org, Andrew Morton , LKML , linux-arch@vger.kernel.org Subject: Re: [PATCH 01/19] tree wide: get rid of __GFP_REPEAT for order-0 allocations part I Message-ID: <20160415074421.GB32377@dhcp22.suse.cz> References: <1460372892-8157-1-git-send-email-mhocko@kernel.org> <1460372892-8157-2-git-send-email-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1857 Lines: 40 On Thu 14-04-16 12:56:28, David Rientjes wrote: > On Mon, 11 Apr 2016, Michal Hocko wrote: > > > From: Michal Hocko > > > > __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@vger.kernel.org > > Signed-off-by: Michal Hocko > > 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. >From what I've seen it was more a copy&paste of the arch code which spread out this flag and there was also a misleading usage. > At the time, I attempted to eliminate __GFP_REPEAT entirely. This is not my plan. I actually want to provide a useful semantic for something like this flag - aka try really hard but eventually fail for all orders and stop being special only for those that are costly. I will call it __GFP_BEST_EFFORT. But I have to clean up the current usage first. Costly orders will keep __GFP_REPEAT because the intent is clear there. All others will lose the flag and then we can start adding __GFP_BEST_EFFORT where it matters also for lower orders. -- Michal Hocko SUSE Labs