While doing MADV_DONTNEED on a large area of thp memory, I noticed we
encountered many unlikely() branches in profiles for each backing
hugepage. This is because zap_pmd_range() would call split_huge_pmd(),
which rechecked the conditions that were already validated, but as part of
an unlikely() branch.
Avoid the unlikely() branch when in a context where pmd is known to be
good for __split_huge_pmd() directly.
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
include/linux/huge_mm.h | 2 ++
mm/memory.c | 4 ++--
mm/mempolicy.c | 2 +-
mm/mprotect.c | 2 +-
4 files changed, 6 insertions(+), 4 deletions(-)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -189,6 +189,8 @@ static inline void deferred_split_huge_page(struct page *page) {}
#define split_huge_pmd(__vma, __pmd, __address) \
do { } while (0)
+static inline void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
+ unsigned long address, bool freeze, struct page *page) {}
static inline void split_huge_pmd_address(struct vm_area_struct *vma,
unsigned long address, bool freeze, struct page *page) {}
diff --git a/mm/memory.c b/mm/memory.c
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1240,7 +1240,7 @@ static inline unsigned long zap_pmd_range(struct mmu_gather *tlb,
if (next - addr != HPAGE_PMD_SIZE) {
VM_BUG_ON_VMA(vma_is_anonymous(vma) &&
!rwsem_is_locked(&tlb->mm->mmap_sem), vma);
- split_huge_pmd(vma, pmd, addr);
+ __split_huge_pmd(vma, pmd, addr, false, NULL);
} else if (zap_huge_pmd(tlb, vma, pmd, addr))
goto next;
/* fall through */
@@ -3454,7 +3454,7 @@ static int wp_huge_pmd(struct fault_env *fe, pmd_t orig_pmd)
/* COW handled on pte level: split pmd */
VM_BUG_ON_VMA(fe->vma->vm_flags & VM_SHARED, fe->vma);
- split_huge_pmd(fe->vma, fe->pmd, fe->address);
+ __split_huge_pmd(fe->vma, fe->pmd, fe->address, false, NULL);
return VM_FAULT_FALLBACK;
}
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -496,7 +496,7 @@ static int queue_pages_pte_range(pmd_t *pmd, unsigned long addr,
page = pmd_page(*pmd);
if (is_huge_zero_page(page)) {
spin_unlock(ptl);
- split_huge_pmd(vma, pmd, addr);
+ __split_huge_pmd(vma, pmd, addr, false, NULL);
} else {
get_page(page);
spin_unlock(ptl);
diff --git a/mm/mprotect.c b/mm/mprotect.c
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -164,7 +164,7 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
if (next - addr != HPAGE_PMD_SIZE) {
- split_huge_pmd(vma, pmd, addr);
+ __split_huge_pmd(vma, pmd, addr, false, NULL);
if (pmd_trans_unstable(pmd))
continue;
} else {
--
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