From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f197.google.com (mail-qt0-f197.google.com [209.85.216.197]) by kanga.kvack.org (Postfix) with ESMTP id 853A66B0522 for ; Wed, 9 May 2018 10:57:23 -0400 (EDT) Received: by mail-qt0-f197.google.com with SMTP id m20-v6so14704632qtm.6 for ; Wed, 09 May 2018 07:57:23 -0700 (PDT) Received: from mail1.bemta8.messagelabs.com (mail1.bemta8.messagelabs.com. [216.82.243.199]) by mx.google.com with ESMTPS id m9si5745230qki.378.2018.05.09.07.57.21 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 09 May 2018 07:57:21 -0700 (PDT) From: Huaisheng HS1 Ye Subject: RE: [External] Re: [PATCH 2/3] include/linux/gfp.h: use unsigned int in gfp_zone Date: Wed, 9 May 2018 14:57:07 +0000 Message-ID: References: <1525416729-108201-1-git-send-email-yehs1@lenovo.com> <1525416729-108201-3-git-send-email-yehs1@lenovo.com> <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> In-Reply-To: <20180507212500.bdphwfhk55w6vlbb@twin.jikos.cz> Content-Language: zh-CN Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox , "dsterba@suse.cz" Cc: 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" > On Mon, May 07, 2018 at 11:44:10AM -0700, Matthew Wilcox wrote: > > On Mon, May 07, 2018 at 05:16:50PM +0000, Huaisheng HS1 Ye wrote: > > > I hope it couldn't cause problem, but based on my analyzation it has = the potential > to go wrong if users still use the flags as usual, which are __GFP_DMA, _= _GFP_DMA32 > and __GFP_HIGHMEM. > > > Let me take an example with my testing platform, these logics are muc= h abstract, > an example will be helpful. > > > > > > There is a two sockets X86_64 server, No HIGHMEM and it has 16 + 16GB= memories. > > > Its zone types shall be like this below, > > > > > > ZONE_DMA 0 0b0000 > > > ZONE_DMA32 1 0b0001 > > > ZONE_NORMAL 2 0b0010 > > > (OPT_ZONE_HIGHMEM) 2 0b0010 > > > ZONE_MOVABLE 3 0b0011 > > > ZONE_DEVICE 4 0b0100 (virtual zone) > > > __MAX_NR_ZONES 5 > > > > > > __GFP_DMA =3D ZONE_DMA ^ ZONE_NORMAL=3D 0b0010 > > > __GFP_DMA32 =3D ZONE_DMA32 ^ ZONE_NORMAL=3D 0b0011 > > > __GFP_HIGHMEM =3D OPT_ZONE_HIGHMEM ^ ZONE_NORMAL =3D 0b0000 > > > __GFP_MOVABLE =3D ZONE_MOVABLE ^ ZONE_NORMAL | ___GFP_MOVABLE =3D 0b1= 001 > > > > > > Eg. > > > If a driver uses flags like this below, > > > Step 1: > > > gfp_mask | __GFP_DMA32; > > > (0b 0000 | 0b 0011 =3D 0b 0011) > > > gfp_mask's low four bits shall equal to 0011, assuming no __GFP_MOVAB= LE > > > > > > Step 2: > > > gfp_mask & ~__GFP_DMA; > > > (0b 0011 & ~0b0010 =3D 0b0001) > > > gfp_mask's low four bits shall equal to 0001 now, then when it enter = gfp_zone(), > > > > > > return ((__force int)flags & ___GFP_ZONE_MASK) ^ ZONE_NORMAL; > > > (0b0001 ^ 0b0010 =3D 0b0011) > > > You know 0011 means that ZONE_MOVABLE will be returned. > > > In this case, error can be found, because gfp_mask needs to get ZONE_= DMA32 originally. > > > But with existing GFP_ZONE_TABLE/BAD, it is correct. Because the bits= are way of > 0x1, 0x2, 0x4, 0x8 > > > > Yes, I understand your point here. My point was that this was already = a bug; > > the caller shouldn't simply be clearing __GFP_DMA; they really mean to = clear > > all of the GFP_ZONE bits so that they allocate from ZONE_NORMAL. And f= or > > that, they should be using ~GFP_ZONEMASK > > > > Unless they already know, of course. For example, this one in > > arch/x86/mm/pgtable.c is fine: > > > > if (strcmp(arg, "nohigh") =3D=3D 0) > > __userpte_alloc_gfp &=3D ~__GFP_HIGHMEM; > > > > because it knows that __userpte_alloc_gfp can only have __GFP_HIGHMEM s= et. > > > > But something like btrfs should almost certainly be using ~GFP_ZONEMASK= . >=20 > 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. >=20 > 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. Hi Matthew, Should we add an error detection in gfp_zone? How about this? @@ -377,6 +377,8 @@ static inline enum zone_type gfp_zone(gfp_t flags) z =3D OPT_ZONE_HIGHMEM + !!((__force unsigned int)flags & ___GFP_MOVABLE); } + + VM_BUG_ON(z > ZONE_MOVABLE); return z; } Sincerely, Huaisheng Ye