The patch titled
Subject: mm/thp: make is_huge_zero_pmd() safe and quicker
has been added to the -mm tree. Its filename is
mm-thp-make-is_huge_zero_pmd-safe-and-quicker.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-thp-make-is_huge_zero_pmd-safe-and-quicker.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-thp-make-is_huge_zero_pmd-safe-and-quicker.patch
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------------------------------------------------------
From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: mm/thp: make is_huge_zero_pmd() safe and quicker
Most callers of is_huge_zero_pmd() supply a pmd already verified present;
but a few (notably zap_huge_pmd()) do not - it might be a pmd migration
entry, in which the pfn is encoded differently from a present pmd: which
might pass the is_huge_zero_pmd() test (though not on x86, since L1TF
forced us to protect against that); or perhaps even crash in pmd_page()
applied to a swap-like entry.
Make it safe by adding pmd_present() check into is_huge_zero_pmd() itself;
and make it quicker by saving huge_zero_pfn, so that is_huge_zero_pmd()
will not need to do that pmd_page() lookup each time.
__split_huge_pmd_locked() checked pmd_trans_huge() before: that worked,
but is unnecessary now that is_huge_zero_pmd() checks present.
Link: https://lkml.kernel.org/r/21ea9ca-a1f5-8b90-5e88-95fb1c49bbfa@xxxxxxxxxx
Fixes: e71769ae5260 ("mm: enable thp migration for shmem thp")
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reviewed-by: Yang Shi <shy828301@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Jue Wang <juew@xxxxxxxxxx>
Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Wang Yugui <wangyugui@xxxxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/huge_mm.h | 8 +++++++-
mm/huge_memory.c | 5 ++++-
2 files changed, 11 insertions(+), 2 deletions(-)
--- a/include/linux/huge_mm.h~mm-thp-make-is_huge_zero_pmd-safe-and-quicker
+++ a/include/linux/huge_mm.h
@@ -286,6 +286,7 @@ struct page *follow_devmap_pud(struct vm
vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf, pmd_t orig_pmd);
extern struct page *huge_zero_page;
+extern unsigned long huge_zero_pfn;
static inline bool is_huge_zero_page(struct page *page)
{
@@ -294,7 +295,7 @@ static inline bool is_huge_zero_page(str
static inline bool is_huge_zero_pmd(pmd_t pmd)
{
- return is_huge_zero_page(pmd_page(pmd));
+ return READ_ONCE(huge_zero_pfn) == pmd_pfn(pmd) && pmd_present(pmd);
}
static inline bool is_huge_zero_pud(pud_t pud)
@@ -439,6 +440,11 @@ static inline bool is_huge_zero_page(str
{
return false;
}
+
+static inline bool is_huge_zero_pmd(pmd_t pmd)
+{
+ return false;
+}
static inline bool is_huge_zero_pud(pud_t pud)
{
--- a/mm/huge_memory.c~mm-thp-make-is_huge_zero_pmd-safe-and-quicker
+++ a/mm/huge_memory.c
@@ -62,6 +62,7 @@ static struct shrinker deferred_split_sh
static atomic_t huge_zero_refcount;
struct page *huge_zero_page __read_mostly;
+unsigned long huge_zero_pfn __read_mostly = ~0UL;
bool transparent_hugepage_enabled(struct vm_area_struct *vma)
{
@@ -98,6 +99,7 @@ retry:
__free_pages(zero_page, compound_order(zero_page));
goto retry;
}
+ WRITE_ONCE(huge_zero_pfn, page_to_pfn(zero_page));
/* We take additional reference here. It will be put back by shrinker */
atomic_set(&huge_zero_refcount, 2);
@@ -147,6 +149,7 @@ static unsigned long shrink_huge_zero_pa
if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
struct page *zero_page = xchg(&huge_zero_page, NULL);
BUG_ON(zero_page == NULL);
+ WRITE_ONCE(huge_zero_pfn, ~0UL);
__free_pages(zero_page, compound_order(zero_page));
return HPAGE_PMD_NR;
}
@@ -2071,7 +2074,7 @@ static void __split_huge_pmd_locked(stru
return;
}
- if (pmd_trans_huge(*pmd) && is_huge_zero_pmd(*pmd)) {
+ if (is_huge_zero_pmd(*pmd)) {
/*
* FIXME: Do we want to invalidate secondary mmu by calling
* mmu_notifier_invalidate_range() see comments below inside
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
mm-thp-fix-__split_huge_pmd_locked-on-shmem-migration-entry.patch
mm-thp-make-is_huge_zero_pmd-safe-and-quicker.patch
mm-thp-try_to_unmap-use-ttu_sync-for-safe-splitting.patch
mm-thp-fix-vma_address-if-virtual-address-below-file-offset.patch
mm-thp-unmap_mapping_page-to-fix-thp-truncate_cleanup_page.patch
mm-page_vma_mapped_walk-use-page-for-pvmw-page.patch
mm-page_vma_mapped_walk-settle-pagehuge-on-entry.patch
mm-page_vma_mapped_walk-use-pmd_read_atomic.patch
mm-page_vma_mapped_walk-use-pmde-for-pvmw-pmd.patch
mm-page_vma_mapped_walk-prettify-pvmw_migration-block.patch
mm-page_vma_mapped_walk-crossing-page-table-boundary.patch
mm-page_vma_mapped_walk-add-a-level-of-indentation.patch
mm-page_vma_mapped_walk-use-goto-instead-of-while-1.patch
mm-page_vma_mapped_walk-get-vma_address_end-earlier.patch
mm-thp-fix-page_vma_mapped_walk-if-thp-mapped-by-ptes.patch
mm-thp-another-pvmw_sync-fix-in-page_vma_mapped_walk.patch
mm-thp-remap_page-is-only-needed-on-anonymous-thp.patch
mm-hwpoison_user_mappings-try_to_unmap-with-ttu_sync.patch
