From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934049AbeEIJjp (ORCPT ); Wed, 9 May 2018 05:39:45 -0400 Received: from mx2.suse.de ([195.135.220.15]:38355 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933758AbeEIJjk (ORCPT ); Wed, 9 May 2018 05:39:40 -0400 Date: Wed, 9 May 2018 11:36:59 +0200 From: David Sterba To: Matthew Wilcox Cc: dsterba@suse.cz, Huaisheng HS1 Ye , Michal Hocko , "akpm@linux-foundation.org" , "linux-mm@kvack.org" , "vbabka@suse.cz" , "mgorman@techsingularity.net" , "pasha.tatashin@oracle.com" , "alexander.levin@verizon.com" , "hannes@cmpxchg.org" , "penguin-kernel@I-love.SAKURA.ne.jp" , "colyli@suse.de" , NingTing Cheng , "linux-kernel@vger.kernel.org" Subject: Re: [External] Re: [PATCH 2/3] include/linux/gfp.h: use unsigned int in gfp_zone Message-ID: <20180509093659.jalprmufpwspya26@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, Matthew Wilcox , Huaisheng HS1 Ye , Michal Hocko , "akpm@linux-foundation.org" , "linux-mm@kvack.org" , "vbabka@suse.cz" , "mgorman@techsingularity.net" , "pasha.tatashin@oracle.com" , "alexander.levin@verizon.com" , "hannes@cmpxchg.org" , "penguin-kernel@I-love.SAKURA.ne.jp" , "colyli@suse.de" , NingTing Cheng , "linux-kernel@vger.kernel.org" References: <20180504133533.GR4535@dhcp22.suse.cz> <20180504154004.GB29829@bombadil.infradead.org> <20180506134814.GB7362@bombadil.infradead.org> <20180506185532.GA13604@bombadil.infradead.org> <20180507184410.GA12361@bombadil.infradead.org> <20180507212500.bdphwfhk55w6vlbb@twin.jikos.cz> <20180508002547.GA16338@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180508002547.GA16338@bombadil.infradead.org> User-Agent: NeoMutt/20180323 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 07, 2018 at 05:25:47PM -0700, Matthew Wilcox wrote: > On Mon, May 07, 2018 at 11:25:01PM +0200, David Sterba wrote: > > On Mon, May 07, 2018 at 11:44:10AM -0700, Matthew Wilcox wrote: > > > But something like btrfs should almost certainly be using ~GFP_ZONEMASK. > > > > Agreed, the direct use of __GFP_DMA32 was added in 3ba7ab220e8918176c6f > > to substitute GFP_NOFS, so the allocation flags are less restrictive but > > still acceptable for allocation from slab. > > > > The requirement from btrfs is to avoid highmem, the 'must be acceptable > > for slab' requirement is more MM internal and should have been hidden > > under some opaque flag mask. There was no strong need for that at the > > time. > > The GFP flags encode a multiple of different requirements. There's > "What can the allocator do to free memory" and "what area of memory > can the allocation come from". btrfs doesn't actually want to > allocate memory from ZONE_MOVABLE or ZONE_DMA either. It's probably never > been called with those particular flags set, but in the spirit of > future-proofing btrfs, perhaps a patch like this is in order? > > ---- >8 ---- > > Subject: btrfs: Allocate extents from ZONE_NORMAL > From: Matthew Wilcox > > If anyone ever passes a GFP_DMA or GFP_MOVABLE allocation flag to > allocate_extent_state, it will try to allocate memory from the wrong zone. > We just want to allocate memory from ZONE_NORMAL, so use GFP_RECLAIM_MASK > to get what we want. Looks good to me. > Signed-off-by: Matthew Wilcox > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > index e99b329002cf..4e4a67b7b29d 100644 > --- a/fs/btrfs/extent_io.c > +++ b/fs/btrfs/extent_io.c > @@ -216,12 +216,7 @@ static struct extent_state *alloc_extent_state(gfp_t mask) > { > struct extent_state *state; > > - /* > - * The given mask might be not appropriate for the slab allocator, > - * drop the unsupported bits > - */ > - mask &= ~(__GFP_DMA32|__GFP_HIGHMEM); I've noticed there's GFP_SLAB_BUG_MASK that's basically open coded here, but this would not filter out the placement flags. > - state = kmem_cache_alloc(extent_state_cache, mask); I'd prefer some comment here, it's not obvious why the mask is used. > + state = kmem_cache_alloc(extent_state_cache, mask & GFP_RECLAIM_MASK); > if (!state) > return state; > state->state = 0;