On 10/19/2016 01:04 AM, David Rientjes wrote:
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.
I'm not sure which unlikely() branch you mean here, as I don't see any in the
split_huge_pmd() macro or the functions it calls? So is it the branches that the
profiler flagged as mispredicted using some PMC event? In that case it's perhaps
confusing to call it "unlikely()".
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 <rient...@google.com>
That said, this makes sense. You could probably convert also:
3 281 mm/gup.c <<follow_page_mask>>
split_huge_pmd(vma, pmd, address);
11 212 mm/mremap.c <<move_page_tables>>
split_huge_pmd(vma, old_pmd, old_addr);
Acked-by: Vlastimil Babka <vba...@suse.cz>
---
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 {
