Re: [PATCH v3 08/14] mm: thp: enable thp migration in generic path

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

On Thu, Feb 09, 2017 at 09:17:01AM -0600, Zi Yan wrote:
> On 9 Feb 2017, at 3:15, Naoya Horiguchi wrote:
> 
> > On Sun, Feb 05, 2017 at 11:12:46AM -0500, Zi Yan wrote:
> >> From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> >>
> >> 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@ah.jp.nec.com>
> >>
> >> ChangeLog v2 -> v3:
> >> - use page_vma_mapped_walk()
> >>
> >> Signed-off-by: Zi Yan <zi.yan@cs.rutgers.edu>
> >> ---
> >>  arch/x86/include/asm/pgtable_64.h |   2 +
> >>  include/linux/swapops.h           |  70 +++++++++++++++++-
> >>  mm/huge_memory.c                  | 151 ++++++++++++++++++++++++++++++++++----
> >>  mm/migrate.c                      |  29 +++++++-
> >>  mm/page_vma_mapped.c              |  13 +++-
> >>  mm/pgtable-generic.c              |   3 +-
> >>  mm/rmap.c                         |  14 +++-
> >>  7 files changed, 259 insertions(+), 23 deletions(-)
> >>
> > ...
> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> >> index 6893c47428b6..fd54bbdc16cf 100644
> >> --- a/mm/huge_memory.c
> >> +++ b/mm/huge_memory.c
> >> @@ -1613,20 +1613,51 @@ int __zap_huge_pmd_locked(struct mmu_gather *tlb, struct vm_area_struct *vma,
> >>  		atomic_long_dec(&tlb->mm->nr_ptes);
> >>  		tlb_remove_page_size(tlb, pmd_page(orig_pmd), HPAGE_PMD_SIZE);
> >>  	} else {
> >> -		struct page *page = pmd_page(orig_pmd);
> >> -		page_remove_rmap(page, true);
> >> -		VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
> >> -		VM_BUG_ON_PAGE(!PageHead(page), page);
> >> -		if (PageAnon(page)) {
> >> -			pgtable_t pgtable;
> >> -			pgtable = pgtable_trans_huge_withdraw(tlb->mm, pmd);
> >> -			pte_free(tlb->mm, pgtable);
> >> -			atomic_long_dec(&tlb->mm->nr_ptes);
> >> -			add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
> >> +		struct page *page;
> >> +		int migration = 0;
> >> +
> >> +		if (!is_pmd_migration_entry(orig_pmd)) {
> >> +			page = pmd_page(orig_pmd);
> >> +			VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
> >> +			VM_BUG_ON_PAGE(!PageHead(page), page);
> >> +			page_remove_rmap(page, true);
> >
> >> +			if (PageAnon(page)) {
> >> +				pgtable_t pgtable;
> >> +
> >> +				pgtable = pgtable_trans_huge_withdraw(tlb->mm,
> >> +								      pmd);
> >> +				pte_free(tlb->mm, pgtable);
> >> +				atomic_long_dec(&tlb->mm->nr_ptes);
> >> +				add_mm_counter(tlb->mm, MM_ANONPAGES,
> >> +					       -HPAGE_PMD_NR);
> >> +			} else {
> >> +				if (arch_needs_pgtable_deposit())
> >> +					zap_deposited_table(tlb->mm, pmd);
> >> +				add_mm_counter(tlb->mm, MM_FILEPAGES,
> >> +					       -HPAGE_PMD_NR);
> >> +			}
> >
> > This block is exactly equal to the one in else block below,
> > So you can factor out into some function.
> 
> Of course, I will do that.
> 
> >
> >>  		} else {
> >> -			if (arch_needs_pgtable_deposit())
> >> -				zap_deposited_table(tlb->mm, pmd);
> >> -			add_mm_counter(tlb->mm, MM_FILEPAGES, -HPAGE_PMD_NR);
> >> +			swp_entry_t entry;
> >> +
> >> +			entry = pmd_to_swp_entry(orig_pmd);
> >> +			page = pfn_to_page(swp_offset(entry));
> >
> >> +			if (PageAnon(page)) {
> >> +				pgtable_t pgtable;
> >> +
> >> +				pgtable = pgtable_trans_huge_withdraw(tlb->mm,
> >> +								      pmd);
> >> +				pte_free(tlb->mm, pgtable);
> >> +				atomic_long_dec(&tlb->mm->nr_ptes);
> >> +				add_mm_counter(tlb->mm, MM_ANONPAGES,
> >> +					       -HPAGE_PMD_NR);
> >> +			} else {
> >> +				if (arch_needs_pgtable_deposit())
> >> +					zap_deposited_table(tlb->mm, pmd);
> >> +				add_mm_counter(tlb->mm, MM_FILEPAGES,
> >> +					       -HPAGE_PMD_NR);
> >> +			}
> >
> >> +			free_swap_and_cache(entry); /* waring in failure? */
> >> +			migration = 1;
> >>  		}
> >>  		tlb_remove_page_size(tlb, page, HPAGE_PMD_SIZE);
> >>  	}
> >> @@ -2634,3 +2665,97 @@ static int __init split_huge_pages_debugfs(void)
> >>  }
> >>  late_initcall(split_huge_pages_debugfs);
> >>  #endif
> >> +
> >> +#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
> >> +void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
> >> +		struct page *page)
> >> +{
> >> +	struct vm_area_struct *vma = pvmw->vma;
> >> +	struct mm_struct *mm = vma->vm_mm;
> >> +	unsigned long address = pvmw->address;
> >> +	pmd_t pmdval;
> >> +	swp_entry_t entry;
> >> +
> >> +	if (pvmw->pmd && !pvmw->pte) {
> >> +		pmd_t pmdswp;
> >> +
> >> +		mmu_notifier_invalidate_range_start(mm, address,
> >> +				address + HPAGE_PMD_SIZE);
> >
> > Don't you have to put mmu_notifier_invalidate_range_* outside this if block?
> 
> I think I need to add mmu_notifier_invalidate_page() in else block.
> 
> Because Kirill's page_vma_mapped_walk() iterates each PMD or PTE.
> In set_pmd_migration_etnry(), if the page is PMD-mapped, it will be called once
> with PMD, then mmu_notifier_invalidate_range_* can be used. On the other hand,
> if the page is PTE-mapped, the function will be called 1~512 times depending
> on how many PTEs are present. mmu_notifier_invalidate_range_* is not suitable.
> mmu_notifier_invalidate_page() on the corresponding subpage should work.
> 

Ah right, mmu_notifier_invalidate_page() is better for PTE-mapped thp.

Thanks,
Naoya
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