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[2003:cb:c707:1400:b7d:4122:28d:f4c3]) by smtp.gmail.com with ESMTPSA id b16-20020adfe650000000b002c5534db60bsm8906826wrn.71.2023.02.15.02.11.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 15 Feb 2023 02:11:52 -0800 (PST) Message-ID: Date: Wed, 15 Feb 2023 11:11:51 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH] mm: page_alloc: don't allocate page from memoryless nodes To: Mike Rapoport 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 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> From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 710431C001B X-Stat-Signature: as8octwqe9zesxxotkrgnedfp1smifyw X-HE-Tag: 1676455918-471033 X-HE-Meta: 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 KC085AOr 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 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 15.02.23 11:04, Mike Rapoport wrote: > 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. I recall where I stumbled over that: commit 3c5f2eb9695cd241c9898a01388b19a149d0b7d2 Author: Heiko Carstens Date: Tue Jul 14 07:46:40 2020 +0200 s390/mm: avoid trimming to MAX_ORDER Trimming to MAX_ORDER was originally done in order to avoid to set HOLES_IN_ZONE, which in turn would enable a quite expensive pfn_valid() check. pfn_valid() however only checks if a struct page exists for a given pfn. With sparsemen vmemmap there are always struct pages, since memmaps are allocated for whole sections. Therefore remove the HOLES_IN_ZONE comment and the trimming. Signed-off-by: Heiko Carstens So indeed, it might just be a legacy leftover and with SPARSEMEM it should all be fine. -- Thanks, David / dhildenb