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* [PATCH v2 0/2] Make alloc_contig_range handle Hugetlb pages
@ 2021-02-18 12:00 Oscar Salvador
  2021-02-18 12:00 ` [PATCH v2 1/2] mm: Make alloc_contig_range handle free hugetlb pages Oscar Salvador
  2021-02-18 12:00 ` [PATCH v2 2/2] mm: Make alloc_contig_range handle in-use " Oscar Salvador
  0 siblings, 2 replies; 5+ messages in thread
From: Oscar Salvador @ 2021-02-18 12:00 UTC (permalink / raw)
  To: Andrew Morton
  Cc: Mike Kravetz, David Hildenbrand, Michal Hocko, Muchun Song,
	linux-mm, linux-kernel, Oscar Salvador

v1 -> v2:
 - Adressed feedback by Michal
 - Restrict the allocation to a node with __GFP_THISNODE
 - Drop PageHuge check in alloc_and_dissolve_huge_page
 - Re-order comments in isolate_or_dissolve_huge_page
 - Extend comment in isolate_migratepages_block
 - Place put_page right after we got the page, otherwise
   dissolve_free_huge_page will fail

 RFC -> v1:
 - Drop RFC
 - Addressed feedback from David and Mike
 - Fence off gigantic pages as there is a cyclic dependency between
   them and alloc_contig_range
 - Re-organize the code to make race-window smaller and to put
   all details in hugetlb code
 - Drop nodemask initialization. First a node will be tried and then we
   will back to other nodes containing memory (N_MEMORY). Details in
   patch#1's changelog
 - Count new page as surplus in case we failed to dissolve the old page
   and the new one. Details in patch#1.

Cover letter:

alloc_contig_range lacks the hability for handling 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 hugepage by allocating a new one
and dissolving the old one.

In-use HugeTLB are no exception though, as those can be isolated and migrated
as any other LRU or Movable page.

This patchset aims for improving alloc_contig_range->isolate_migratepages_block,
so HugeTLB pages can be recognized and handled.

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"

Oscar Salvador (2):
  mm: Make alloc_contig_range handle free hugetlb pages
  mm: Make alloc_contig_range handle in-use hugetlb pages

 include/linux/hugetlb.h |  7 +++++
 mm/compaction.c         | 22 ++++++++++++++
 mm/hugetlb.c            | 77 +++++++++++++++++++++++++++++++++++++++++++++++++
 mm/vmscan.c             |  5 ++--
 4 files changed, 109 insertions(+), 2 deletions(-)

-- 
2.16.3



^ permalink raw reply	[flat|nested] 5+ messages in thread

end of thread, other threads:[~2021-02-19  6:08 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-02-18 12:00 [PATCH v2 0/2] Make alloc_contig_range handle Hugetlb pages Oscar Salvador
2021-02-18 12:00 ` [PATCH v2 1/2] mm: Make alloc_contig_range handle free hugetlb pages Oscar Salvador
2021-02-19  2:10   ` Mike Kravetz
2021-02-19  6:08     ` Oscar Salvador
2021-02-18 12:00 ` [PATCH v2 2/2] mm: Make alloc_contig_range handle in-use " Oscar Salvador

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