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bh=+40pgbNx1mfVdszd2dJGbIj51cHRI+hvUPY1VqaVb1c=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=B75bhV0SZSZkVkNzkLMg+bXOBR9kv/dwTgZcuqbbgC0MOOFVbXRLd5B4lOOfJyMfk NHMDSSkgNkSJhIA7JY06MEJ0ZuOqfXPk3WE+sFpquBCC9Z3L4fLKEQEPdMO8qunsZ4 dT/4LRnxrQNrs4hPXOuuFbfYw+Fi+R6f+4E1S1sF9u5jTFHdQaRXSuwa++DEH9cAb8 TGPPt/BQ0AlgKlza1BZg0UiqPBiop8/5Z2ck5XFVnmQ+i2zFKZ2ZeaTIRBW9T9HKg3 G8JkNEawIUojXz1TcsNgY+cKwwKFZh3GQfZ/Qme13PGZK0kj4tnGVcOjn/2Dbt2eqA OcwAG64AR5ZqQ== Date: Wed, 15 Feb 2023 12:04:54 +0200 From: Mike Rapoport To: David Hildenbrand Cc: Michal Hocko , Qi Zheng , Qi Zheng , Vlastimil Babka , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Teng Hu , Matthew Wilcox , Mel Gorman , Oscar Salvador , Muchun Song , x86@kernel.org Subject: Re: [PATCH] mm: page_alloc: don't allocate page from memoryless nodes Message-ID: References: <67240e55-af49-f20a-2b4b-b7d574cd910d@gmail.com> <22f0e262-982e-ea80-e52a-a3c924b31d58@redhat.com> <4386151c-0328-d207-9a71-933ef61817f9@redhat.com> <3a85b2b9-95fa-4123-a7a3-2bd6f8b35c13@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3a85b2b9-95fa-4123-a7a3-2bd6f8b35c13@redhat.com> X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: cruiusx3gt1y1pupw8sk5byzr7hfaxpq X-Rspamd-Queue-Id: B9FFD140011 X-HE-Tag: 1676455511-946786 X-HE-Meta: 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 tc3PSyCD 35bjQN8km/TXFt+csMUKafZJ7z72/nXEGzCiwmonUp7id0mum82op0LZjuK7N6i813jzSW9H+B7sUk7El2hLqxNkvGa5f0W28J3t8Q8dWEHnlNOBV+NLkt7ydOZxLikQ/IwVnPBUoAtnnvqplo9BQDtcO0DfqAOs3WO9KqrZ7yuMQDQDwNoCaKgbId6EyoB4ZhjavcaAgVV+agPq7ZwdvtAg6QMcSTJry+ojsRZHdppxR+lhTnO9jfu9uH9GxCPN2CApfm2UwFFEXYnQxh2k8kWDpi8cBzuBt3hY9LtIQkOX34ibgfSlWYojCTtrmmnXs2RWfM1hz3JWF2HaBOKBJncbuPLk8RtkAHX4vbGCy+LltItc0IsmEUQABag/7bCeZGXwvkzInmvI+qCMzNKI25K6LI33t9kDnggvO1g9zucrf2ritSTufy0EcnHFRlgpf1aLz0CpXwviPxWJaUOfiUAnhePEhiT7FJSIlOpB9FlfL5VhTwjTGwOeUPh7vpss0hc3X94MF0D1m8dpLNzf/Pw1DFTRA2VvzixdNRtY+UyHn+lF4aeCVOkCFFY7idLd93GjN X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Feb 15, 2023 at 10:43:58AM +0100, David Hildenbrand wrote: > On 15.02.23 10:30, Mike Rapoport wrote: > > On Tue, Feb 14, 2023 at 02:38:44PM +0100, Michal Hocko wrote: > > > On Tue 14-02-23 12:58:39, David Hildenbrand wrote: > > > > On 14.02.23 12:48, David Hildenbrand wrote: > > > > > On 14.02.23 12:44, Mike Rapoport wrote: > > > > > > (added x86 folks) > > > > > > > > > > > > On Tue, Feb 14, 2023 at 12:29:42PM +0100, David Hildenbrand wrote: > > > > > > > On 14.02.23 12:26, Qi Zheng wrote: > > > > > > > > On 2023/2/14 19:22, David Hildenbrand wrote: > > > > > > > > > > > > > > > > > > TBH, this is the first time I hear of NODE_MIN_SIZE and it seems to be a > > > > > > > > > pretty x86 specific thing. > > > > > > > > > > > > > > > > > > Are we sure we want to get NODE_MIN_SIZE involved? > > > > > > > > > > > > > > > > Maybe add an arch_xxx() to handle it? > > > > > > > > > > > > > > I still haven't figured out what we want to achieve with NODE_MIN_SIZE at > > > > > > > all. It smells like an arch-specific hack looking at > > > > > > > > > > > > > > "Don't confuse VM with a node that doesn't have the minimum amount of > > > > > > > memory" > > > > > > > > > > > > > > Why shouldn't mm-core deal with that? > > > > > > > > > > > > Well, a node with <4M RAM is not very useful and bears all the overhead of > > > > > > an extra live node. > > > > > > > > > > And totally not with 4.1M, haha. > > > > > > > > > > I really like the "Might fix boot" in the commit description. > > > > > > > > > > > > > > > > > But, hey, why won't we just drop that '< NODE_MIN_SIZE' and let people with > > > > > > weird HW configurations just live with this? > > > > > > > > > > > > > > > ;) > > > > > > > > > > > > > Actually, remembering 09f49dca570a ("mm: handle uninitialized numa nodes > > > > gracefully"), this might be the right thing to do. That commit assumes that > > > > all offline nodes would get the pgdat allocated in free_area_init(). So that > > > > we end up with an allocated pgdat for all possible nodes. The reasoning IIRC > > > > was that we don't care about wasting memory in weird VM setups. > > > > > > Yes, that is the case indeed. I suspect the NODE_MIN_SIZE is a relict of > > > the past when some PXM entries were incorrect or fishy. I would just > > > drop the check and see whether something breaks. Or make those involved > > > back then remember whether this is addressing something that is relevant > > > these days. Even 5MB node makes (as the memmap is allocated for the > > > whole memory section anyway and that is 128MB) a very little sense if you ask me. > > > > How about we try this: > > > > From b670120bcacd3fe34a40d7179c70ca2ab69279e0 Mon Sep 17 00:00:00 2001 > > From: "Mike Rapoport (IBM)" > > Date: Wed, 15 Feb 2023 11:12:18 +0200 > > Subject: [PATCH] x86/mm: drop 4MB restriction on minimal NUMA node size > > > > Qi Zheng reports crashes in a production environment and provides a > > simplified example as a reproducer: > > > > For example, if we use qemu to start a two NUMA node kernel, > > one of the nodes has 2M memory (less than NODE_MIN_SIZE), > > and the other node has 2G, then we will encounter the > > following panic: > > > > [ 0.149844] BUG: kernel NULL pointer dereference, address: 0000000000000000 > > [ 0.150783] #PF: supervisor write access in kernel mode > > [ 0.151488] #PF: error_code(0x0002) - not-present page > > <...> > > [ 0.156056] RIP: 0010:_raw_spin_lock_irqsave+0x22/0x40 > > <...> > > [ 0.169781] Call Trace: > > [ 0.170159] > > [ 0.170448] deactivate_slab+0x187/0x3c0 > > [ 0.171031] ? bootstrap+0x1b/0x10e > > [ 0.171559] ? preempt_count_sub+0x9/0xa0 > > [ 0.172145] ? kmem_cache_alloc+0x12c/0x440 > > [ 0.172735] ? bootstrap+0x1b/0x10e > > [ 0.173236] bootstrap+0x6b/0x10e > > [ 0.173720] kmem_cache_init+0x10a/0x188 > > [ 0.174240] start_kernel+0x415/0x6ac > > [ 0.174738] secondary_startup_64_no_verify+0xe0/0xeb > > [ 0.175417] > > [ 0.175713] Modules linked in: > > [ 0.176117] CR2: 0000000000000000 > > > > The crashes happen because of inconsistency between nodemask that has > > nodes with less than 4MB as memoryless and the actual memory fed into > > core mm. > > > > The commit 9391a3f9c7f1 ("[PATCH] x86_64: Clear more state when ignoring > > empty node in SRAT parsing") that introduced minimal size of a NUMA node > > does not explain why a node size cannot be less than 4MB and what boot > > failures this restriction might fix. > > > > Since then a lot has changed and core mm won't confuse badly about small > > node sizes. > > > > Drop the limitation for the minimal node size. > > > > Link: https://lore.kernel.org/all/20230212110305.93670-1-zhengqi.arch@bytedance.com/ > > Signed-off-by: Mike Rapoport (IBM) > > --- > > arch/x86/include/asm/numa.h | 7 ------- > > arch/x86/mm/numa.c | 7 ------- > > 2 files changed, 14 deletions(-) > > > > diff --git a/arch/x86/include/asm/numa.h b/arch/x86/include/asm/numa.h > > index e3bae2b60a0d..ef2844d69173 100644 > > --- a/arch/x86/include/asm/numa.h > > +++ b/arch/x86/include/asm/numa.h > > @@ -12,13 +12,6 @@ > > #define NR_NODE_MEMBLKS (MAX_NUMNODES*2) > > -/* > > - * Too small node sizes may confuse the VM badly. Usually they > > - * result from BIOS bugs. So dont recognize nodes as standalone > > - * NUMA entities that have less than this amount of RAM listed: > > - */ > > -#define NODE_MIN_SIZE (4*1024*1024) > > - > > extern int numa_off; > > /* > > diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c > > index 2aadb2019b4f..55e3d895f15c 100644 > > --- a/arch/x86/mm/numa.c > > +++ b/arch/x86/mm/numa.c > > @@ -601,13 +601,6 @@ static int __init numa_register_memblks(struct numa_meminfo *mi) > > if (start >= end) > > continue; > > - /* > > - * Don't confuse VM with a node that doesn't have the > > - * minimum amount of memory: > > - */ > > - if (end && (end - start) < NODE_MIN_SIZE) > > - continue; > > - > > alloc_node_data(nid); > > } > > Hopefully it fixes the issue. > > Acked-by: David Hildenbrand > > > The 4 MiB looks like the magical MAX_ORDER (and/or pageblock) thingy to me. > I recall that there were issues in the past when memory exposed to the buddy > would only be partially covering a pageblock. IIRC, memblock should already > take care to not expose memory to the buddy that is not aligned to MAX_ORDER > boundaries -- correct? I don't remember those issues, but memblock does not align memory freed to the buddy. Still, this 4MB looks like a really old magic that was way before memblock and even SPARSEMEM was experimental back then. It's possible that the issues were with DISCONTIGMEM or with bootmem. > -- > Thanks, > > David / dhildenb > -- Sincerely yours, Mike.