Messages in this thread | | | Date | Sun, 28 Nov 2021 20:31:35 -0800 | Subject | Re: Commit 'hugetlbfs: extend the definition of hugepages parameter to support node allocation' breaks old numa less syntax of reserving hugepages on boot. | From | Mike Kravetz <> |
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On 11/28/21 03:18, Maxim Levitsky wrote: > > dmesg prints this: > > HugeTLB: allocating 64 of page size 1.00 GiB failed. Only allocated 0 hugepages > > Huge pages were allocated on kernel command line (1/2 of 128GB system): > > 'default_hugepagesz=1G hugepagesz=1G hugepages=64' > > This is 3970X and no real support/need for NUMA, thus only fake NUMA node 0 is present. > > Reverting the commit helps. > > New syntax also works ( hugepages=0:64 ) > > I can test any patches for this bug.
Argh! I think preallocation of gigantic pages on all systems with only a single node is broken. The issue is at the beginning of __alloc_bootmem_huge_page:
int __alloc_bootmem_huge_page(struct hstate *h, int nid) { struct huge_bootmem_page *m = NULL; /* initialize for clang */ int nr_nodes, node;
if (nid >= nr_online_nodes) return 0;
Without using the node specific syntax, nid == NUMA_NO_NODE == -1. For the comparison, nid will be converted to an unsigned into to match nr_online_nodes so we will immediately return 0 instead of doing the allocations.
Zhenguo Yao, Can you verify and perhaps put together a patch?does
> > Also unrelated, is there any progress on allocating 1GB pages on demand so that I could > allocate them only when I run a VM?
That should be possible. Such support was added back in 2014 with commit 944d9fec8d7a "hugetlb: add support for gigantic page allocation at runtime".
> > i don't mind having these pages to be marked as to be used for userspace only, > since as far as I remember its the kernel usage that makes some page unmoveable. >
Of course, finding 1GB of contiguous space for a gigantic page is often difficult at runtime. So, allocations are likely to fail the longer the system is up and running and fragmentation increases.
> Last time (many years ago) I tried to create a zone with only userspace pages > (I don't remember what options I used) but it didn't work.
Not too long ago, support was added to use CMA for gigantic page allocation. See commit cf11e85fc08c "mm: hugetlb: optionally allocate gigantic hugepages using cma". This sounds like something you might want to try. -- Mike Kravetz
> > Is there a way to debug what is causing unmoveable pages and doesn't let > /proc/sys/vm/nr_hugepages work (I tried it today and as usual the number > it can allocate steadly decreases over time).
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