From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-f199.google.com (mail-pf1-f199.google.com [209.85.210.199]) by kanga.kvack.org (Postfix) with ESMTP id 162EE6B0003 for ; Fri, 19 Oct 2018 04:07:04 -0400 (EDT) Received: by mail-pf1-f199.google.com with SMTP id y73-v6so17782238pfi.16 for ; Fri, 19 Oct 2018 01:07:04 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id j65-v6si22117874pge.589.2018.10.19.01.07.02 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 19 Oct 2018 01:07:02 -0700 (PDT) Date: Fri, 19 Oct 2018 10:06:57 +0200 From: Michal Hocko Subject: Re: [PATCH 2/2] mm, thp: consolidate THP gfp handling into alloc_hugepage_direct_gfpmask Message-ID: <20181019080657.GJ18839@dhcp22.suse.cz> References: <20180925120326.24392-1-mhocko@kernel.org> <20180925120326.24392-3-mhocko@kernel.org> <20180926133039.y7o5x4nafovxzh2s@kshutemo-mobl1> <20180926141708.GX6278@dhcp22.suse.cz> <20180926142227.GZ6278@dhcp22.suse.cz> <20181018191147.33e8d5e1ebd785c06aab7b30@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181018191147.33e8d5e1ebd785c06aab7b30@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: "Kirill A. Shutemov" , Mel Gorman , Vlastimil Babka , David Rientjes , Andrea Argangeli , Zi Yan , Stefan Priebe - Profihost AG , linux-mm@kvack.org, LKML On Thu 18-10-18 19:11:47, Andrew Morton wrote: > On Wed, 26 Sep 2018 16:22:27 +0200 Michal Hocko wrote: > > > > MPOL_PREFERRED is handled by policy_node() before we call __alloc_pages_nodemask. > > > __GFP_THISNODE is applied only when we are not using > > > __GFP_DIRECT_RECLAIM which is handled in alloc_hugepage_direct_gfpmask > > > now. > > > Lastly MPOL_BIND wasn't handled explicitly but in the end the removed > > > late check would remove __GFP_THISNODE for it as well. So in the end we > > > are doing the same thing unless I miss something > > > > Forgot to add. One notable exception would be that the previous code > > would allow to hit > > WARN_ON_ONCE(policy->mode == MPOL_BIND && (gfp & __GFP_THISNODE)); > > in policy_node if the requested node (e.g. cpu local one) was outside of > > the mbind nodemask. This is not possible now. We haven't heard about any > > such warning yet so it is unlikely that it happens though. > > Perhaps a changelog addition is needed to cover the above? : THP allocation mode is quite complex and it depends on the defrag : mode. This complexity is hidden in alloc_hugepage_direct_gfpmask from a : large part currently. The NUMA special casing (namely __GFP_THISNODE) is : however independent and placed in alloc_pages_vma currently. This both : adds an unnecessary branch to all vma based page allocation requests and : it makes the code more complex unnecessarily as well. Not to mention : that e.g. shmem THP used to do the node reclaiming unconditionally : regardless of the defrag mode until recently. This was not only : unexpected behavior but it was also hardly a good default behavior and I : strongly suspect it was just a side effect of the code sharing more than : a deliberate decision which suggests that such a layering is wrong. : : Moreover the oriinal code allowed to trigger : WARN_ON_ONCE(policy->mode == MPOL_BIND && (gfp & __GFP_THISNODE)); : in policy_node if the requested node (e.g. cpu local one) was outside of : the mbind nodemask. This is not possible now. We haven't heard about any : such warning yet so it is unlikely that it happens but still a signal of : a wrong code layering. : : Get rid of the thp special casing from alloc_pages_vma and move the logic : to alloc_hugepage_direct_gfpmask. __GFP_THISNODE is applied to : the resulting gfp mask only when the direct reclaim is not requested and : when there is no explicit numa binding to preserve the current logic. : : This allows for removing alloc_hugepage_vma as well. Better? > I assume that David's mbind() concern has gone away. Either I've misunderstood it or it was not really a real issue. -- Michal Hocko SUSE Labs