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* [PATCH 0/3] powerpc/mm/hash: Time improvements for memory hot(un)plug
@ 2021-03-12  7:29 Leonardo Bras
  2021-03-12  7:29 ` [PATCH 1/3] powerpc/mm/hash: Avoid resizing-down HPT on first memory hotplug Leonardo Bras
                   ` (2 more replies)
  0 siblings, 3 replies; 12+ messages in thread
From: Leonardo Bras @ 2021-03-12  7:29 UTC (permalink / raw)
  To: Michael Ellerman, Benjamin Herrenschmidt, Paul Mackerras,
	Andrew Morton, Leonardo Bras, Sandipan Das, Aneesh Kumar K.V,
	Logan Gunthorpe, Mike Rapoport, Bharata B Rao, Dan Williams,
	Nicholas Piggin, Nathan Lynch, David Hildenbrand, Laurent Dufour,
	Scott Cheloha, David Gibson
  Cc: linuxppc-dev, linux-kernel

This patchset intends to reduce time needed for processing memory
hotplug/hotunplug in hash guests.

The first one, makes sure guests with pagesize over 4k don't need to
go through HPT resize-downs after memory hotplug.

The second and third patches make hotplug / hotunplug perform a single
HPT resize per operation, instead of one for each shift change, or one
for each LMB in case of resize-down error.

Why haven't the same mechanism used for both memory hotplug and hotunplug?
They both have different requirements:

Memory hotplug causes (usually) HPT resize-ups, which are fine happening
at the start of hotplug, but resize-ups should not ever be disabled, as
other mechanisms may try to increase memory, hitting issues with a HPT
that is too small.

Memory hotunplug causes HPT resize-downs, which can be disabled (HPT will
just remain larger for a while), but need to happen at the end of an
hotunplug operation. If we want to batch it, we need to disable
resize-downs and perform it only at the end.

Tests done with this patchset in the same machine / guest config:
Starting memory: 129GB, DIMM: 256GB
Before patchset: hotplug = 710s, hotunplug = 621s.
After patchset: hotplug  = 21s, hotunplug = 100s.

Any feedback will be appreciated!
I believe the code may not be very well placed in available files,
so please give some feedback on that.

Best regards,

Leonardo Bras (3):
  powerpc/mm/hash: Avoid resizing-down HPT on first memory hotplug
  powerpc/mm/hash: Avoid multiple HPT resize-ups on memory hotplug
  powerpc/mm/hash: Avoid multiple HPT resize-downs on memory hotunplug

 arch/powerpc/include/asm/book3s/64/hash.h     |  4 +
 arch/powerpc/include/asm/sparsemem.h          |  4 +
 arch/powerpc/mm/book3s64/hash_utils.c         | 78 +++++++++++++++----
 arch/powerpc/mm/book3s64/pgtable.c            | 18 +++++
 .../platforms/pseries/hotplug-memory.c        | 22 ++++++
 5 files changed, 111 insertions(+), 15 deletions(-)

-- 
2.29.2


^ permalink raw reply	[flat|nested] 12+ messages in thread

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2021-03-12  7:29 [PATCH 0/3] powerpc/mm/hash: Time improvements for memory hot(un)plug Leonardo Bras
2021-03-12  7:29 ` [PATCH 1/3] powerpc/mm/hash: Avoid resizing-down HPT on first memory hotplug Leonardo Bras
2021-03-22  6:49   ` David Gibson
2021-04-09  2:16     ` Leonardo Bras
2021-03-12  7:29 ` [PATCH 2/3] powerpc/mm/hash: Avoid multiple HPT resize-ups on " Leonardo Bras
2021-03-22  7:55   ` David Gibson
2021-04-09  2:51     ` Leonardo Bras
2021-04-19  5:34       ` David Gibson
2021-03-12  7:29 ` [PATCH 3/3] powerpc/mm/hash: Avoid multiple HPT resize-downs on memory hotunplug Leonardo Bras
2021-03-22 23:45   ` David Gibson
2021-04-09  3:31     ` Leonardo Bras
2021-04-19  5:37       ` David Gibson

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