Commit 50722804 authored by Zach O'Keefe's avatar Zach O'Keefe Committed by Andrew Morton
Browse files

mm/khugepaged: record SCAN_PMD_MAPPED when scan_pmd() finds hugepage 

When scanning an anon pmd to see if it's eligible for collapse, return
SCAN_PMD_MAPPED if the pmd already maps a hugepage.  Note that
SCAN_PMD_MAPPED is different from SCAN_PAGE_COMPOUND used in the
file-collapse path, since the latter might identify pte-mapped compound
pages.  This is required by MADV_COLLAPSE which necessarily needs to know
what hugepage-aligned/sized regions are already pmd-mapped.

In order to determine if a pmd already maps a hugepage, refactor
mm_find_pmd():

Return mm_find_pmd() to it's pre-commit f72e7dcd ("mm: let mm_find_pmd
fix buggy race with THP fault") behavior.  ksm was the only caller that
explicitly wanted a pte-mapping pmd, so open code the pte-mapping logic
there (pmd_present() and pmd_trans_huge() checks).

Undo revert change in commit f72e7dcd ("mm: let mm_find_pmd fix buggy
race with THP fault") that open-coded split_huge_pmd_address() pmd lookup
and use mm_find_pmd() instead.

Link: https://lkml.kernel.org/r/20220706235936.2197195-9-zokeefe@google.com


Signed-off-by: default avatarZach O'Keefe <zokeefe@google.com>
Reviewed-by: default avatarYang Shi <shy828301@gmail.com>
Cc: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Chris Kennelly <ckennelly@google.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Pavel Begunkov <asml.silence@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rongwei Wang <rongwei.wang@linux.alibaba.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: "Souptick Joarder (HPE)" <jrdr.linux@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent a7f4e6e4

include/trace/events/huge_memory.h

+1 −0
Original line number Diff line number Diff line
@@ -11,6 +11,7 @@ 
	EM( SCAN_FAIL,			"failed")			\

	EM( SCAN_SUCCEED,		"succeeded")			\

	EM( SCAN_PMD_NULL,		"pmd_null")			\

	EM( SCAN_PMD_MAPPED,		"page_pmd_mapped")		\

	EM( SCAN_EXCEED_NONE_PTE,	"exceed_none_pte")		\

	EM( SCAN_EXCEED_SWAP_PTE,	"exceed_swap_pte")		\

	EM( SCAN_EXCEED_SHARED_PTE,	"exceed_shared_pte")		\

mm/huge_memory.c

+2 −16
Original line number Diff line number Diff line
@@ -2286,25 +2286,11 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, 
void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address,

		bool freeze, struct folio *folio)

{

	pgd_t *pgd;

	p4d_t *p4d;

	pud_t *pud;

	pmd_t *pmd;

	pmd_t *pmd = mm_find_pmd(vma->vm_mm, address);



	pgd = pgd_offset(vma->vm_mm, address);

	if (!pgd_present(*pgd))

	if (!pmd)

		return;



	p4d = p4d_offset(pgd, address);

	if (!p4d_present(*p4d))

		return;



	pud = pud_offset(p4d, address);

	if (!pud_present(*pud))

		return;



	pmd = pmd_offset(pud, address);



	__split_huge_pmd(vma, pmd, address, freeze, folio);

}

mm/internal.h

+1 −1
Original line number Diff line number Diff line
@@ -187,7 +187,7 @@ extern void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason 
/*

 * in mm/rmap.c:

 */

extern pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address);

pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address);



/*

 * in mm/page_alloc.c

mm/khugepaged.c

+48 −12
Original line number Diff line number Diff line
@@ -28,6 +28,7 @@ enum scan_result { 
	SCAN_FAIL,

	SCAN_SUCCEED,

	SCAN_PMD_NULL,

	SCAN_PMD_MAPPED,

	SCAN_EXCEED_NONE_PTE,

	SCAN_EXCEED_SWAP_PTE,

	SCAN_EXCEED_SHARED_PTE,
@@ -877,6 +878,45 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address, 
	return SCAN_SUCCEED;

}



static int find_pmd_or_thp_or_none(struct mm_struct *mm,

				   unsigned long address,

				   pmd_t **pmd)

{

	pmd_t pmde;



	*pmd = mm_find_pmd(mm, address);

	if (!*pmd)

		return SCAN_PMD_NULL;



	pmde = pmd_read_atomic(*pmd);



#ifdef CONFIG_TRANSPARENT_HUGEPAGE

	/* See comments in pmd_none_or_trans_huge_or_clear_bad() */

	barrier();

#endif

	if (!pmd_present(pmde))

		return SCAN_PMD_NULL;

	if (pmd_trans_huge(pmde))

		return SCAN_PMD_MAPPED;

	if (pmd_bad(pmde))

		return SCAN_PMD_NULL;

	return SCAN_SUCCEED;

}



static int check_pmd_still_valid(struct mm_struct *mm,

				 unsigned long address,

				 pmd_t *pmd)

{

	pmd_t *new_pmd;

	int result = find_pmd_or_thp_or_none(mm, address, &new_pmd);



	if (result != SCAN_SUCCEED)

		return result;

	if (new_pmd != pmd)

		return SCAN_FAIL;

	return SCAN_SUCCEED;

}



/*

 * Bring missing pages in from swap, to complete THP collapse.

 * Only done if khugepaged_scan_pmd believes it is worthwhile.
@@ -988,9 +1028,8 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address, 
		goto out_nolock;

	}



	pmd = mm_find_pmd(mm, address);

	if (!pmd) {

		result = SCAN_PMD_NULL;

	result = find_pmd_or_thp_or_none(mm, address, &pmd);

	if (result != SCAN_SUCCEED) {

		mmap_read_unlock(mm);

		goto out_nolock;

	}
@@ -1018,7 +1057,8 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address, 
	if (result != SCAN_SUCCEED)

		goto out_up_write;

	/* check if the pmd is still valid */

	if (mm_find_pmd(mm, address) != pmd)

	result = check_pmd_still_valid(mm, address, pmd);

	if (result != SCAN_SUCCEED)

		goto out_up_write;



	anon_vma_lock_write(vma->anon_vma);
@@ -1121,11 +1161,9 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, struct vm_area_struct *vma, 


	VM_BUG_ON(address & ~HPAGE_PMD_MASK);



	pmd = mm_find_pmd(mm, address);

	if (!pmd) {

		result = SCAN_PMD_NULL;

	result = find_pmd_or_thp_or_none(mm, address, &pmd);

	if (result != SCAN_SUCCEED)

		goto out;

	}



	memset(cc->node_load, 0, sizeof(cc->node_load));

	pte = pte_offset_map_lock(mm, pmd, address, &ptl);
@@ -1383,8 +1421,7 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr) 
	if (!PageHead(hpage))

		goto drop_hpage;



	pmd = mm_find_pmd(mm, haddr);

	if (!pmd)

	if (find_pmd_or_thp_or_none(mm, haddr, &pmd) != SCAN_SUCCEED)

		goto drop_hpage;



	start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl);
@@ -1502,8 +1539,7 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff) 
		if (vma->vm_end < addr + HPAGE_PMD_SIZE)

			continue;

		mm = vma->vm_mm;

		pmd = mm_find_pmd(mm, addr);

		if (!pmd)

		if (find_pmd_or_thp_or_none(mm, addr, &pmd) != SCAN_SUCCEED)

			continue;

		/*

		 * We need exclusive mmap_lock to retract page table.

mm/ksm.c

+10 −0
Original line number Diff line number Diff line
@@ -1134,6 +1134,7 @@ static int replace_page(struct vm_area_struct *vma, struct page *page, 
{

	struct mm_struct *mm = vma->vm_mm;

	pmd_t *pmd;

	pmd_t pmde;

	pte_t *ptep;

	pte_t newpte;

	spinlock_t *ptl;
@@ -1148,6 +1149,15 @@ static int replace_page(struct vm_area_struct *vma, struct page *page, 
	pmd = mm_find_pmd(mm, addr);

	if (!pmd)

		goto out;

	/*

	 * Some THP functions use the sequence pmdp_huge_clear_flush(), set_pmd_at()

	 * without holding anon_vma lock for write.  So when looking for a

	 * genuine pmde (in which to find pte), test present and !THP together.

	 */

	pmde = *pmd;

	barrier();

	if (!pmd_present(pmde) || pmd_trans_huge(pmde))

		goto out;



	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm, addr,

				addr + PAGE_SIZE);