Re: [PATCH v3 00/14] mm: page migration enhancement for thp

[Zi Yan <zi.yan@cs.rutgers.edu>]

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Ping.

Just want to get comments on THP migration part (Patch 4-14). If they
look OK, I can rebase THP migration part on mmotm-2017-02-22-16-28 and
send them out for merging.

Thanks.

Zi Yan wrote:
> From: Zi Yan <ziy@nvidia.com>
> 
> Hi all,
> 
> The patches are rebased on mmotm-2017-02-01-15-35 with feedbacks from 
> Naoya Horiguchi's v2 patches.
> 
> I fix a bug in zap_pmd_range() and include the fixes in Patches 1-3.
> The racy check in zap_pmd_range() can miss pmd_protnone and pmd_migration_entry,
> which leads to PTE page table not freed.
> 
> In Patch 4, I move _PAGE_SWP_SOFT_DIRTY to bit 1. Because bit 6 (used in v2)
> can be set by some CPUs by mistake and the new swap entry format does not use
> bit 1-4.
> 
> I also adjust two core migration functions, set_pmd_migration_entry() and
> remove_migration_pmd(), to use Kirill A. Shutemov's page_vma_mapped_walk()
> function. Patch 8 needs Kirill's comments, since I also add changes
> to his page_vma_mapped_walk() function with pmd_migration_entry handling.
> 
> In Patch 8, I replace pmdp_huge_get_and_clear() with pmdp_huge_clear_flush()
> in set_pmd_migration_entry() to avoid data corruption after page migration.
> 
> In Patch 9, I include is_pmd_migration_entry() in pmd_none_or_trans_huge_or_clear_bad().
> Otherwise, a pmd_migration_entry is treated as pmd_bad and cleared, which
> leads to deposited PTE page table not freed.
> 
> I personally use this patchset with my customized kernel to test frequent
> page migrations by replacing page reclaim with page migration.
> The bugs fixed in Patches 1-3 and 8 was discovered while I am testing my kernel.
> I did a 16-hour stress test that has ~7 billion total page migrations.
> No error or data corruption was found. 
> 
> 
> General description 
> ===========================================
> 
> This patchset enhances page migration functionality to handle thp migration
> for various page migration's callers:
>  - mbind(2)
>  - move_pages(2)
>  - migrate_pages(2)
>  - cgroup/cpuset migration
>  - memory hotremove
>  - soft offline
> 
> The main benefit is that we can avoid unnecessary thp splits, which helps us
> avoid performance decrease when your applications handles NUMA optimization on
> their own.
> 
> The implementation is similar to that of normal page migration, the key point
> is that we modify a pmd to a pmd migration entry in swap-entry like format.
> 
> 
> Any comments or advices are welcomed.
> 
> Best Regards,
> Yan Zi
> 
> Naoya Horiguchi (11):
>   mm: x86: move _PAGE_SWP_SOFT_DIRTY from bit 7 to bit 1
>   mm: mempolicy: add queue_pages_node_check()
>   mm: thp: introduce separate TTU flag for thp freezing
>   mm: thp: introduce CONFIG_ARCH_ENABLE_THP_MIGRATION
>   mm: thp: enable thp migration in generic path
>   mm: thp: check pmd migration entry in common path
>   mm: soft-dirty: keep soft-dirty bits over thp migration
>   mm: hwpoison: soft offline supports thp migration
>   mm: mempolicy: mbind and migrate_pages support thp migration
>   mm: migrate: move_pages() supports thp migration
>   mm: memory_hotplug: memory hotremove supports thp migration
> 
> Zi Yan (3):
>   mm: thp: make __split_huge_pmd_locked visible.
>   mm: thp: create new __zap_huge_pmd_locked function.
>   mm: use pmd lock instead of racy checks in zap_pmd_range()
> 
>  arch/x86/Kconfig                     |   4 +
>  arch/x86/include/asm/pgtable.h       |  17 ++
>  arch/x86/include/asm/pgtable_64.h    |   2 +
>  arch/x86/include/asm/pgtable_types.h |  10 +-
>  arch/x86/mm/gup.c                    |   4 +-
>  fs/proc/task_mmu.c                   |  37 +++--
>  include/asm-generic/pgtable.h        | 105 ++++--------
>  include/linux/huge_mm.h              |  36 ++++-
>  include/linux/rmap.h                 |   1 +
>  include/linux/swapops.h              | 146 ++++++++++++++++-
>  mm/Kconfig                           |   3 +
>  mm/gup.c                             |  20 ++-
>  mm/huge_memory.c                     | 302 +++++++++++++++++++++++++++++------
>  mm/madvise.c                         |   2 +
>  mm/memcontrol.c                      |   2 +
>  mm/memory-failure.c                  |  31 ++--
>  mm/memory.c                          |  33 ++--
>  mm/memory_hotplug.c                  |  17 +-
>  mm/mempolicy.c                       | 124 ++++++++++----
>  mm/migrate.c                         |  66 ++++++--
>  mm/mprotect.c                        |   6 +-
>  mm/mremap.c                          |   2 +-
>  mm/page_vma_mapped.c                 |  13 +-
>  mm/pagewalk.c                        |   2 +
>  mm/pgtable-generic.c                 |   3 +-
>  mm/rmap.c                            |  21 ++-
>  26 files changed, 770 insertions(+), 239 deletions(-)
> 

-- 
Best Regards,
Yan Zi


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