Commit e90309c9 authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Linus Torvalds
Browse files

thp: allow mlocked THP again 



Before THP refcounting rework, THP was not allowed to cross VMA
boundary.  So, if we have THP and we split it, PG_mlocked can be safely
transferred to small pages.

With new THP refcounting and naive approach to mlocking we can end up
with this scenario:
 1. we have a mlocked THP, which belong to one VM_LOCKED VMA.
 2. the process does munlock() on the *part* of the THP:
      - the VMA is split into two, one of them VM_LOCKED;
      - huge PMD split into PTE table;
      - THP is still mlocked;
 3. split_huge_page():
      - it transfers PG_mlocked to *all* small pages regrardless if it
	blong to any VM_LOCKED VMA.

We probably could munlock() all small pages on split_huge_page(), but I
think we have accounting issue already on step two.

Instead of forbidding mlocked pages altogether, we just avoid mlocking
PTE-mapped THPs and munlock THPs on split_huge_pmd().

This means PTE-mapped THPs will be on normal lru lists and will be split
under memory pressure by vmscan.  After the split vmscan will detect
unevictable small pages and mlock them.

With this approach we shouldn't hit situation like described above.

Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Steve Capper <steve.capper@linaro.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a46e6376

mm/gup.c

+4 −2
Original line number Diff line number Diff line
@@ -143,6 +143,10 @@ retry: 
		mark_page_accessed(page);

	}

	if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {

		/* Do not mlock pte-mapped THP */

		if (PageTransCompound(page))

			goto out;



		/*

		 * The preliminary mapping check is mainly to avoid the

		 * pointless overhead of lock_page on the ZERO_PAGE
@@ -920,8 +924,6 @@ long populate_vma_page_range(struct vm_area_struct *vma, 
	gup_flags = FOLL_TOUCH | FOLL_POPULATE | FOLL_MLOCK;

	if (vma->vm_flags & VM_LOCKONFAULT)

		gup_flags &= ~FOLL_POPULATE;

	if (vma->vm_flags & VM_LOCKED)

		gup_flags |= FOLL_SPLIT;

	/*

	 * We want to touch writable mappings with a write fault in order

	 * to break COW, except for shared mappings because these don't COW

mm/huge_memory.c

+30 −7
Original line number Diff line number Diff line
@@ -874,8 +874,6 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma, 


	if (haddr < vma->vm_start || haddr + HPAGE_PMD_SIZE > vma->vm_end)

		return VM_FAULT_FALLBACK;

	if (vma->vm_flags & VM_LOCKED)

		return VM_FAULT_FALLBACK;

	if (unlikely(anon_vma_prepare(vma)))

		return VM_FAULT_OOM;

	if (unlikely(khugepaged_enter(vma, vma->vm_flags)))
@@ -1344,7 +1342,20 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma, 
			update_mmu_cache_pmd(vma, addr, pmd);

	}

	if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {

		if (page->mapping && trylock_page(page)) {

		/*

		 * We don't mlock() pte-mapped THPs. This way we can avoid

		 * leaking mlocked pages into non-VM_LOCKED VMAs.

		 *

		 * In most cases the pmd is the only mapping of the page as we

		 * break COW for the mlock() -- see gup_flags |= FOLL_WRITE for

		 * writable private mappings in populate_vma_page_range().

		 *

		 * The only scenario when we have the page shared here is if we

		 * mlocking read-only mapping shared over fork(). We skip

		 * mlocking such pages.

		 */

		if (compound_mapcount(page) == 1 && !PageDoubleMap(page) &&

				page->mapping && trylock_page(page)) {

			lru_add_drain();

			if (page->mapping)

				mlock_vma_page(page);
@@ -2209,8 +2220,6 @@ static bool hugepage_vma_check(struct vm_area_struct *vma) 
	if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||

	    (vma->vm_flags & VM_NOHUGEPAGE))

		return false;

	if (vma->vm_flags & VM_LOCKED)

		return false;

	if (!vma->anon_vma || vma->vm_ops)

		return false;

	if (is_vma_temporary_stack(vma))
@@ -2851,14 +2860,28 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, 
{

	spinlock_t *ptl;

	struct mm_struct *mm = vma->vm_mm;

	struct page *page = NULL;

	unsigned long haddr = address & HPAGE_PMD_MASK;



	mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE);

	ptl = pmd_lock(mm, pmd);

	if (likely(pmd_trans_huge(*pmd)))

	if (unlikely(!pmd_trans_huge(*pmd)))

		goto out;

	page = pmd_page(*pmd);

	__split_huge_pmd_locked(vma, pmd, haddr, false);

	if (PageMlocked(page))

		get_page(page);

	else

		page = NULL;

out:

	spin_unlock(ptl);

	mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE);

	if (page) {

		lock_page(page);

		munlock_vma_page(page);

		unlock_page(page);

		put_page(page);

	}

}



static void split_huge_pmd_address(struct vm_area_struct *vma,

mm/memory.c

+3 −3
Original line number Diff line number Diff line
@@ -2160,14 +2160,14 @@ static int wp_page_copy(struct mm_struct *mm, struct vm_area_struct *vma, 


	pte_unmap_unlock(page_table, ptl);

	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);

	/* THP pages are never mlocked */

	if (old_page && !PageTransCompound(old_page)) {

	if (old_page) {

		/*

		 * Don't let another task, with possibly unlocked vma,

		 * keep the mlocked page.

		 */

		if (page_copied && (vma->vm_flags & VM_LOCKED)) {

			lock_page(old_page);	/* LRU manipulation */

			if (PageMlocked(old_page))

				munlock_vma_page(old_page);

			unlock_page(old_page);

		}

mm/mlock.c

+47 −21
Original line number Diff line number Diff line
@@ -82,6 +82,9 @@ void mlock_vma_page(struct page *page) 
	/* Serialize with page migration */

	BUG_ON(!PageLocked(page));



	VM_BUG_ON_PAGE(PageTail(page), page);

	VM_BUG_ON_PAGE(PageCompound(page) && PageDoubleMap(page), page);



	if (!TestSetPageMlocked(page)) {

		mod_zone_page_state(page_zone(page), NR_MLOCK,

				    hpage_nr_pages(page));
@@ -178,6 +181,8 @@ unsigned int munlock_vma_page(struct page *page) 
	/* For try_to_munlock() and to serialize with page migration */

	BUG_ON(!PageLocked(page));



	VM_BUG_ON_PAGE(PageTail(page), page);



	/*

	 * Serialize with any parallel __split_huge_page_refcount() which

	 * might otherwise copy PageMlocked to part of the tail pages before
@@ -388,6 +393,13 @@ static unsigned long __munlock_pagevec_fill(struct pagevec *pvec, 
		if (!page || page_zone_id(page) != zoneid)

			break;



		/*

		 * Do not use pagevec for PTE-mapped THP,

		 * munlock_vma_pages_range() will handle them.

		 */

		if (PageTransCompound(page))

			break;



		get_page(page);

		/*

		 * Increase the address that will be returned *before* the
@@ -443,7 +455,22 @@ void munlock_vma_pages_range(struct vm_area_struct *vma, 
		page = follow_page_mask(vma, start, FOLL_GET | FOLL_DUMP,

				&page_mask);



		if (page && !IS_ERR(page) && !PageTransCompound(page)) {

		if (page && !IS_ERR(page)) {

			if (PageTransTail(page)) {

				VM_BUG_ON_PAGE(PageMlocked(page), page);

				put_page(page); /* follow_page_mask() */

			} else if (PageTransHuge(page)) {

				lock_page(page);

				/*

				 * Any THP page found by follow_page_mask() may

				 * have gotten split before reaching

				 * munlock_vma_page(), so we need to recompute

				 * the page_mask here.

				 */

				page_mask = munlock_vma_page(page);

				unlock_page(page);

				put_page(page); /* follow_page_mask() */

			} else {

				/*

				 * Non-huge pages are handled in batches via

				 * pagevec. The pin from follow_page_mask()
@@ -464,8 +491,7 @@ void munlock_vma_pages_range(struct vm_area_struct *vma, 
				__munlock_pagevec(&pvec, zone);

				goto next;

			}

		/* It's a bug to munlock in the middle of a THP page */

		VM_BUG_ON((start >> PAGE_SHIFT) & page_mask);

		}

		page_increm = 1 + page_mask;

		start += page_increm * PAGE_SIZE;

next:

mm/rmap.c

+3 −0
Original line number Diff line number Diff line
@@ -1282,6 +1282,9 @@ static void page_remove_anon_compound_rmap(struct page *page) 
		nr = HPAGE_PMD_NR;

	}



	if (unlikely(PageMlocked(page)))

		clear_page_mlock(page);



	if (nr) {

		__mod_zone_page_state(page_zone(page), NR_ANON_PAGES, -nr);

		deferred_split_huge_page(page);

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