From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-f179.google.com (mail-we0-f179.google.com [74.125.82.179]) by kanga.kvack.org (Postfix) with ESMTP id 0B3D66B0031 for ; Tue, 17 Jun 2014 11:30:35 -0400 (EDT) Received: by mail-we0-f179.google.com with SMTP id w62so7292761wes.24 for ; Tue, 17 Jun 2014 08:30:35 -0700 (PDT) Received: from zene.cmpxchg.org (zene.cmpxchg.org. [2a01:238:4224:fa00:ca1f:9ef3:caee:a2bd]) by mx.google.com with ESMTPS id df7si13075919wib.45.2014.06.17.08.30.33 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Tue, 17 Jun 2014 08:30:33 -0700 (PDT) Date: Tue, 17 Jun 2014 11:30:18 -0400 From: Johannes Weiner Subject: Re: [patch 03/12] mm: huge_memory: use GFP_TRANSHUGE when charging huge pages Message-ID: <20140617153018.GA7331@cmpxchg.org> References: <1402948472-8175-1-git-send-email-hannes@cmpxchg.org> <1402948472-8175-4-git-send-email-hannes@cmpxchg.org> <20140617134745.GB19886@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140617134745.GB19886@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Andrew Morton , Hugh Dickins , Tejun Heo , Vladimir Davydov , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Tue, Jun 17, 2014 at 03:47:45PM +0200, Michal Hocko wrote: > On Mon 16-06-14 15:54:23, Johannes Weiner wrote: > > Transparent huge page charges prefer falling back to regular pages > > rather than spending a lot of time in direct reclaim. > > > > Desired reclaim behavior is usually declared in the gfp mask, but THP > > charges use GFP_KERNEL and then rely on the fact that OOM is disabled > > for THP charges, and that OOM-disabled charges currently skip reclaim. > > OOM-disabled charges do one round of reclaim currently. Oops, fixed in v4. > > Needless to say, this is anything but obvious and quite error prone. > > > > Convert THP charges to use GFP_TRANSHUGE instead, which implies > > __GFP_NORETRY, to indicate the low-latency requirement. > > OK, this makes sense. It would be ideal if we could use the same gfp as > for allocation but that would be too much churn I guess because some > allocator use a allocation helper which deduces proper gfp flags without > giving them back to the caller. > > Nevertheless, I would still prefer if 05/12 was moved before > this patch because this is strictly speaking a behavior change. Yes, that's bungled up, thanks for catching that. So here is the order I put it in (reverse git history order of course): commit d0d31c8d4f4cf91edcffa704e8c65ca62af24cf8 Author: Johannes Weiner Date: Mon Apr 14 08:16:09 2014 -0400 mm: memcontrol: retry reclaim for oom-disabled and __GFP_NOFAIL charges There is no reason why oom-disabled and __GFP_NOFAIL charges should try to reclaim only once when every other charge tries several times before giving up. Make them all retry the same number of times. Signed-off-by: Johannes Weiner commit 69f5c6c1a6553a04d7701012a73b2477df8d5a19 Author: Johannes Weiner Date: Thu Jun 5 22:02:26 2014 -0400 mm: huge_memory: use GFP_TRANSHUGE when charging huge pages Transparent huge page charges prefer falling back to regular pages rather than spending a lot of time in direct reclaim. Desired reclaim behavior is usually declared in the gfp mask, but THP charges use GFP_KERNEL and then rely on the fact that OOM is disabled for THP charges, and that OOM-disabled charges don't retry reclaim. Needless to say, this is anything but obvious and quite error prone. Convert THP charges to use GFP_TRANSHUGE instead, which implies __GFP_NORETRY, to indicate the low-latency requirement. Signed-off-by: Johannes Weiner Acked-by: Michal Hocko commit d485e6b4ed62885d54c57c18c5427e2f174c9012 Author: Johannes Weiner Date: Tue May 27 15:23:18 2014 -0400 mm: memcontrol: reclaim at least once for __GFP_NORETRY Currently, __GFP_NORETRY tries charging once and gives up before even trying to reclaim. Bring the behavior on par with the page allocator and reclaim at least once before giving up. Signed-off-by: Johannes Weiner Acked-by: Michal Hocko This first changes __GFP_NORETRY to provide THP-required semantics, then switches THP over to it, then fixes oom-disabled/NOFAIL charges. Does that make more sense? > > Signed-off-by: Johannes Weiner > > Anyway > Acked-by: Michal Hocko Thanks! -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org