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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 f72e7dcdd2 ("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 f72e7dcdd2 ("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: Zach O'Keefe <zokeefe@google.com>
Reviewed-by: Yang 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: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Zach O'Keefe 2022-07-06 16:59:26 -07:00 committed by Andrew Morton
parent a7f4e6e4c4
commit 5072280442
6 changed files with 67 additions and 39 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/trace/events/huge_memory.h
View File

@ -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") \

18
mm/huge_memory.c
View File

@ -2286,25 +2286,11 @@ out:
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);
}

2
mm/internal.h
View File

@ -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

60
mm/khugepaged.c
View File

@ -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.

10
mm/ksm.c
View File

@ -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);

15
mm/rmap.c
View File

@ -767,13 +767,17 @@ unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
return vma_address(page, vma);
}
/*
* Returns the actual pmd_t* where we expect 'address' to be mapped from, or
* NULL if it doesn't exist. No guarantees / checks on what the pmd_t*
* represents.
*/
pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address)
{
pgd_t *pgd;
p4d_t *p4d;
pud_t *pud;
pmd_t *pmd = NULL;
pmd_t pmde;
pgd = pgd_offset(mm, address);
if (!pgd_present(*pgd))
@ -788,15 +792,6 @@ pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address)
goto out;
pmd = pmd_offset(pud, address);
/*
* 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))
pmd = NULL;
out:
return pmd;
}