On Sat, Jul 01, 2017 at 09:40:03AM -0400, Zi Yan wrote:
> From: Zi Yan <zi.yan@xxxxxxxxxxxxxx>
>
> This patch adds thp migration's core code, including conversions
> between a PMD entry and a swap entry, setting PMD migration entry,
> removing PMD migration entry, and waiting on PMD migration entries.
>
> This patch makes it possible to support thp migration.
> If you fail to allocate a destination page as a thp, you just split
> the source thp as we do now, and then enter the normal page migration.
> If you succeed to allocate destination thp, you enter thp migration.
> Subsequent patches actually enable thp migration for each caller of
> page migration by allowing its get_new_page() callback to
> allocate thps.
>
> ChangeLog v1 -> v2:
> - support pte-mapped thp, doubly-mapped thp
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
>
> ChangeLog v2 -> v3:
> - use page_vma_mapped_walk()
> - use pmdp_huge_clear_flush() instead of pmdp_huge_get_and_clear() in
> set_pmd_migration_entry()
>
> ChangeLog v3 -> v4:
> - factor out the code of removing pte pgtable page in zap_huge_pmd()
>
> ChangeLog v4 -> v5:
> - remove unnecessary PTE-mapped THP code in remove_migration_pmd()
> and set_pmd_migration_entry()
> - restructure the code in zap_huge_pmd() to avoid factoring out
> the pte pgtable page code
> - in zap_huge_pmd(), check that PMD swap entries are migration entries
> - change author information
>
> ChangeLog v5 -> v7
> - use macro to disable the code when thp migration is not enabled
>
> ChangeLog v7 -> v8
> - use IS_ENABLED instead of macro to make code look clean in
> zap_huge_pmd() and page_vma_mapped_walk()
> - remove BUILD_BUG() in pmd_to_swp_entry() and swp_entry_to_pmd() to
> avoid compilation error
> - rename variable 'migration' to 'flush_needed' and invert the logic in
> zap_huge_pmd() to make code more descriptive
> - use pmdp_invalidate() in set_pmd_migration_entry() to avoid race
> with MADV_DONTNEED
> - remove unnecessary tlb flush in remove_migration_pmd()
> - add the missing migration flag check in page_vma_mapped_walk()
>
> Signed-off-by: Zi Yan <zi.yan@xxxxxxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
> arch/x86/include/asm/pgtable_64.h | 2 +
> include/linux/swapops.h | 67 ++++++++++++++++++++++++++++++-
> mm/huge_memory.c | 84 ++++++++++++++++++++++++++++++++++++---
> mm/migrate.c | 32 ++++++++++++++-
> mm/page_vma_mapped.c | 18 +++++++--
> mm/pgtable-generic.c | 3 +-
> mm/rmap.c | 13 ++++++
> 7 files changed, 207 insertions(+), 12 deletions(-)
>
...
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 91948fbbb0bb..b28f633cd569 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1302,6 +1302,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
> bool ret = true;
> enum ttu_flags flags = (enum ttu_flags)arg;
>
> +
> /* munlock has nothing to gain from examining un-locked vmas */
> if ((flags & TTU_MUNLOCK) && !(vma->vm_flags & VM_LOCKED))
> return true;
> @@ -1312,6 +1313,18 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
> }
>
> while (page_vma_mapped_walk(&pvmw)) {
> +#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
> + /* PMD-mapped THP migration entry */
> + if (flags & TTU_MIGRATION) {
My testing based on mmotm-2017-07-06-16-18 showed that migrating shmem thp
caused kernel crash. I don't think this is critical because that case is
just not-prepared yet. So in order to avoid the crash, please add
PageAnon(page) check here. This makes shmem thp migration just fail.
+ if (!PageAnon(page))
+ continue;
> + if (!pvmw.pte && page) {
Just from curiosity, do we really need this page check?
try_to_unmap() always passes down the parameter 'page' to try_to_unmap_one()
via rmap_walk_* family, so I think we can assume page is always non-NULL.
Thanks,
Naoya Horiguchi
> + VM_BUG_ON_PAGE(PageHuge(page) || !PageTransCompound(page),
> + page);
> + set_pmd_migration_entry(&pvmw, page);
> + continue;
> + }
> + }
> +#endif
> +
> /*
> * If the page is mlock()d, we cannot swap it out.
> * If it's recently referenced (perhaps page_referenced
> --
> 2.11.0
>
>
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