Messages in this thread | | | Date | Wed, 15 Feb 2023 10:43:58 +0100 | Subject | Re: [PATCH] mm: page_alloc: don't allocate page from memoryless nodes | From | David Hildenbrand <> |
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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)" <rppt@kernel.org> > 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] <TASK> > [ 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] </TASK> > [ 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) <rppt@kernel.org> > --- > 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 <david@redhat.com>
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?
-- Thanks,
David / dhildenb
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