When scanning an anon pmd to see if it's eligible for collapse, return
SCAN_PMD_MAPPED if the pmd already maps a THP. 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.
Signed-off-by: Zach O'Keefe <zokeefe@xxxxxxxxxx>
---
include/trace/events/huge_memory.h | 3 ++-
mm/internal.h | 1 +
mm/khugepaged.c | 30 ++++++++++++++++++++++++++----
mm/rmap.c | 15 +++++++++++++--
4 files changed, 42 insertions(+), 7 deletions(-)
diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h
index d651f3437367..9faa678e0a5b 100644
--- a/include/trace/events/huge_memory.h
+++ b/include/trace/events/huge_memory.h
@@ -33,7 +33,8 @@
EM( SCAN_ALLOC_HUGE_PAGE_FAIL, "alloc_huge_page_failed") \
EM( SCAN_CGROUP_CHARGE_FAIL, "ccgroup_charge_failed") \
EM( SCAN_TRUNCATED, "truncated") \
- EMe(SCAN_PAGE_HAS_PRIVATE, "page_has_private") \
+ EM( SCAN_PAGE_HAS_PRIVATE, "page_has_private") \
+ EMe(SCAN_PMD_MAPPED, "page_pmd_mapped") \
#undef EM
#undef EMe
diff --git a/mm/internal.h b/mm/internal.h
index 1d3fb3c0f971..db594d611925 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -172,6 +172,7 @@ extern void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason
/*
* in mm/rmap.c:
*/
+pmd_t *mm_find_pmd_raw(struct mm_struct *mm, unsigned long address);
extern pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address);
/*
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 0cde4b44d799..b403f056a847 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -51,6 +51,7 @@ enum scan_result {
SCAN_CGROUP_CHARGE_FAIL,
SCAN_TRUNCATED,
SCAN_PAGE_HAS_PRIVATE,
+ SCAN_PMD_MAPPED,
};
#define CREATE_TRACE_POINTS
@@ -987,6 +988,29 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
return 0;
}
+static int find_pmd_or_thp_or_none(struct mm_struct *mm,
+ unsigned long address,
+ pmd_t **pmd)
+{
+ *pmd = mm_find_pmd_raw(mm, address);
+ pmd_t pmde;
+
+ 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) || pmd_none(pmde))
+ return SCAN_PMD_NULL;
+ if (pmd_trans_huge(pmde))
+ return SCAN_PMD_MAPPED;
+ return SCAN_SUCCEED;
+}
+
/*
* Bring missing pages in from swap, to complete THP collapse.
* Only done if khugepaged_scan_pmd believes it is worthwhile.
@@ -1238,11 +1262,9 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
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(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
pte = pte_offset_map_lock(mm, pmd, address, &ptl);
diff --git a/mm/rmap.c b/mm/rmap.c
index a1211fa879cf..fb47443f44c6 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -758,13 +758,12 @@ unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
return vma_address(page, vma);
}
-pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address)
+pmd_t *mm_find_pmd_raw(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))
@@ -779,6 +778,18 @@ pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address)
goto out;
pmd = pmd_offset(pud, address);
+out:
+ return pmd;
+}
+
+pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address)
+{
+ pmd_t pmde;
+ pmd_t *pmd;
+
+ pmd = mm_find_pmd_raw(mm, address);
+ 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
--
2.35.1.1178.g4f1659d476-goog
