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c8e28b47af
Patch series "Make alloc_contig_range handle Hugetlb pages", v10.
alloc_contig_range lacks the ability to handle HugeTLB pages. This can
be problematic for some users, e.g: CMA and virtio-mem, where those
users will fail the call if alloc_contig_range ever sees a HugeTLB page,
even when those pages lay in ZONE_MOVABLE and are free. That problem
can be easily solved by replacing the page in the free hugepage pool.
In-use HugeTLB are no exception though, as those can be isolated and
migrated as any other LRU or Movable page.
This aims to improve alloc_contig_range->isolate_migratepages_block, so
that HugeTLB pages can be recognized and handled.
Since we also need to start reporting errors down the chain (e.g:
-ENOMEM due to not be able to allocate a new hugetlb page),
isolate_migratepages_{range,block} interfaces need to change to start
reporting error codes instead of the pfn == 0 vs pfn != 0 scheme it is
using right now. From now on, isolate_migratepages_block will not
return the next pfn to be scanned anymore, but -EINTR, -ENOMEM or 0, so
we the next pfn to be scanned will be recorded in cc->migrate_pfn field
(as it is already done in isolate_migratepages_range()).
Below is an insight from David (thanks), where the problem can clearly be
seen:
"Start a VM with 4G. Hotplug 1G via virtio-mem and online it to
ZONE_MOVABLE. Allocate 512 huge pages.
[root@localhost ~]# cat /proc/meminfo
MemTotal: 5061512 kB
MemFree: 3319396 kB
MemAvailable: 3457144 kB
...
HugePages_Total: 512
HugePages_Free: 512
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
The huge pages get partially allocate from ZONE_MOVABLE. Try unplugging
1G via virtio-mem (remember, all ZONE_MOVABLE). Inside the guest:
[ 180.058992] alloc_contig_range: [1b8000, 1c0000) PFNs busy
[ 180.060531] alloc_contig_range: [1b8000, 1c0000) PFNs busy
[ 180.061972] alloc_contig_range: [1b8000, 1c0000) PFNs busy
[ 180.063413] alloc_contig_range: [1b8000, 1c0000) PFNs busy
[ 180.064838] alloc_contig_range: [1b8000, 1c0000) PFNs busy
[ 180.065848] alloc_contig_range: [1bfc00, 1c0000) PFNs busy
[ 180.066794] alloc_contig_range: [1bfc00, 1c0000) PFNs busy
[ 180.067738] alloc_contig_range: [1bfc00, 1c0000) PFNs busy
[ 180.068669] alloc_contig_range: [1bfc00, 1c0000) PFNs busy
[ 180.069598] alloc_contig_range: [1bfc00, 1c0000) PFNs busy"
And then with this patchset running:
"Same experiment with ZONE_MOVABLE:
a) Free huge pages: all memory can get unplugged again.
b) Allocated/populated but idle huge pages: all memory can get unplugged
again.
c) Allocated/populated but all 512 huge pages are read/written in a
loop: all memory can get unplugged again, but I get a single
[ 121.192345] alloc_contig_range: [180000, 188000) PFNs busy
Most probably because it happened to try migrating a huge page
while it was busy. As virtio-mem retries on ZONE_MOVABLE a couple of
times, it can deal with this temporary failure.
Last but not least, I did something extreme:
# cat /proc/meminfo
MemTotal: 5061568 kB
MemFree: 186560 kB
MemAvailable: 354524 kB
...
HugePages_Total: 2048
HugePages_Free: 2048
HugePages_Rsvd: 0
HugePages_Surp: 0
Triggering unplug would require to dissolve+alloc - which now fails
when trying to allocate an additional ~512 huge pages (1G).
As expected, I can properly see memory unplug not fully succeeding. +
I get a fairly continuous stream of
[ 226.611584] alloc_contig_range: [19f400, 19f800) PFNs busy
...
But more importantly, the hugepage count remains stable, as configured
by the admin (me):
HugePages_Total: 2048
HugePages_Free: 2048
HugePages_Rsvd: 0
HugePages_Surp: 0"
This patch (of 7):
Currently, __alloc_contig_migrate_range can generate -EINTR, -ENOMEM or
-EBUSY, and report them down the chain. The problem is that when
migrate_pages() reports -ENOMEM, we keep going till we exhaust all the
try-attempts (5 at the moment) instead of bailing out.
migrate_pages() bails out right away on -ENOMEM because it is considered a
fatal error. Do the same here instead of keep going and retrying. Note
that this is not fixing a real issue, just a cosmetic change. Although we
can save some cycles by backing off ealier
Link: https://lkml.kernel.org/r/20210419075413.1064-1-osalvador@suse.de
Link: https://lkml.kernel.org/r/20210419075413.1064-2-osalvador@suse.de
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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|---|---|---|
| .. | ||
| kasan | ||
| kfence | ||
| backing-dev.c | ||
| balloon_compaction.c | ||
| cleancache.c | ||
| cma_debug.c | ||
| cma.c | ||
| cma.h | ||
| compaction.c | ||
| debug_page_ref.c | ||
| debug_vm_pgtable.c | ||
| debug.c | ||
| dmapool.c | ||
| early_ioremap.c | ||
| fadvise.c | ||
| failslab.c | ||
| filemap.c | ||
| frontswap.c | ||
| gup_test.c | ||
| gup_test.h | ||
| gup.c | ||
| highmem.c | ||
| hmm.c | ||
| huge_memory.c | ||
| hugetlb_cgroup.c | ||
| hugetlb.c | ||
| hwpoison-inject.c | ||
| init-mm.c | ||
| internal.h | ||
| interval_tree.c | ||
| io-mapping.c | ||
| ioremap.c | ||
| Kconfig | ||
| Kconfig.debug | ||
| khugepaged.c | ||
| kmemleak.c | ||
| ksm.c | ||
| list_lru.c | ||
| maccess.c | ||
| madvise.c | ||
| Makefile | ||
| mapping_dirty_helpers.c | ||
| memblock.c | ||
| memcontrol.c | ||
| memfd.c | ||
| memory_hotplug.c | ||
| memory-failure.c | ||
| memory.c | ||
| mempolicy.c | ||
| mempool.c | ||
| memremap.c | ||
| memtest.c | ||
| migrate.c | ||
| mincore.c | ||
| mlock.c | ||
| mm_init.c | ||
| mmap_lock.c | ||
| mmap.c | ||
| mmu_gather.c | ||
| mmu_notifier.c | ||
| mmzone.c | ||
| mprotect.c | ||
| mremap.c | ||
| msync.c | ||
| nommu.c | ||
| oom_kill.c | ||
| page_alloc.c | ||
| page_counter.c | ||
| page_ext.c | ||
| page_idle.c | ||
| page_io.c | ||
| page_isolation.c | ||
| page_owner.c | ||
| page_poison.c | ||
| page_reporting.c | ||
| page_reporting.h | ||
| page_vma_mapped.c | ||
| page-writeback.c | ||
| pagewalk.c | ||
| percpu-internal.h | ||
| percpu-km.c | ||
| percpu-stats.c | ||
| percpu-vm.c | ||
| percpu.c | ||
| pgalloc-track.h | ||
| pgtable-generic.c | ||
| process_vm_access.c | ||
| ptdump.c | ||
| readahead.c | ||
| rmap.c | ||
| rodata_test.c | ||
| shmem.c | ||
| shuffle.c | ||
| shuffle.h | ||
| slab_common.c | ||
| slab.c | ||
| slab.h | ||
| slob.c | ||
| slub.c | ||
| sparse-vmemmap.c | ||
| sparse.c | ||
| swap_cgroup.c | ||
| swap_slots.c | ||
| swap_state.c | ||
| swap.c | ||
| swapfile.c | ||
| truncate.c | ||
| usercopy.c | ||
| userfaultfd.c | ||
| util.c | ||
| vmacache.c | ||
| vmalloc.c | ||
| vmpressure.c | ||
| vmscan.c | ||
| vmstat.c | ||
| workingset.c | ||
| z3fold.c | ||
| zbud.c | ||
| zpool.c | ||
| zsmalloc.c | ||
| zswap.c | ||