On 11 Jul 2017, at 2:47, Naoya Horiguchi wrote: > On Sat, Jul 01, 2017 at 09:40:03AM -0400, Zi Yan wrote: >> From: Zi Yan >> >> 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 >> >> 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 >> Cc: Kirill A. Shutemov >> --- >> 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; > Thanks for your testing. I will add this check in my next version. >> + 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. You are right. Checking page is not necessary here. I will remove it in my next version. -- Best Regards Yan Zi