thp: optimize away unnecessary page table locking
Currently when we check if we can handle thp as it is or we need to split
it into regular sized pages, we hold page table lock prior to check
whether a given pmd is mapping thp or not. Because of this, when it's not
"huge pmd" we suffer from unnecessary lock/unlock overhead. To remove it,
this patch introduces a optimized check function and replace several
similar logics with it.
[akpm@linux-foundation.org: checkpatch fixes]
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8f7fc39..f0e5306 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1031,32 +1031,23 @@
{
int ret = 0;
- spin_lock(&tlb->mm->page_table_lock);
- if (likely(pmd_trans_huge(*pmd))) {
- if (unlikely(pmd_trans_splitting(*pmd))) {
- spin_unlock(&tlb->mm->page_table_lock);
- wait_split_huge_page(vma->anon_vma,
- pmd);
- } else {
- struct page *page;
- pgtable_t pgtable;
- pgtable = get_pmd_huge_pte(tlb->mm);
- page = pmd_page(*pmd);
- pmd_clear(pmd);
- tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
- page_remove_rmap(page);
- VM_BUG_ON(page_mapcount(page) < 0);
- add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
- VM_BUG_ON(!PageHead(page));
- tlb->mm->nr_ptes--;
- spin_unlock(&tlb->mm->page_table_lock);
- tlb_remove_page(tlb, page);
- pte_free(tlb->mm, pgtable);
- ret = 1;
- }
- } else
+ if (__pmd_trans_huge_lock(pmd, vma) == 1) {
+ struct page *page;
+ pgtable_t pgtable;
+ pgtable = get_pmd_huge_pte(tlb->mm);
+ page = pmd_page(*pmd);
+ pmd_clear(pmd);
+ tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
+ page_remove_rmap(page);
+ VM_BUG_ON(page_mapcount(page) < 0);
+ add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
+ VM_BUG_ON(!PageHead(page));
+ tlb->mm->nr_ptes--;
spin_unlock(&tlb->mm->page_table_lock);
-
+ tlb_remove_page(tlb, page);
+ pte_free(tlb->mm, pgtable);
+ ret = 1;
+ }
return ret;
}
@@ -1066,21 +1057,15 @@
{
int ret = 0;
- spin_lock(&vma->vm_mm->page_table_lock);
- if (likely(pmd_trans_huge(*pmd))) {
- ret = !pmd_trans_splitting(*pmd);
+ if (__pmd_trans_huge_lock(pmd, vma) == 1) {
+ /*
+ * All logical pages in the range are present
+ * if backed by a huge page.
+ */
spin_unlock(&vma->vm_mm->page_table_lock);
- if (unlikely(!ret))
- wait_split_huge_page(vma->anon_vma, pmd);
- else {
- /*
- * All logical pages in the range are present
- * if backed by a huge page.
- */
- memset(vec, 1, (end - addr) >> PAGE_SHIFT);
- }
- } else
- spin_unlock(&vma->vm_mm->page_table_lock);
+ memset(vec, 1, (end - addr) >> PAGE_SHIFT);
+ ret = 1;
+ }
return ret;
}
@@ -1110,20 +1095,11 @@
goto out;
}
- spin_lock(&mm->page_table_lock);
- if (likely(pmd_trans_huge(*old_pmd))) {
- if (pmd_trans_splitting(*old_pmd)) {
- spin_unlock(&mm->page_table_lock);
- wait_split_huge_page(vma->anon_vma, old_pmd);
- ret = -1;
- } else {
- pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
- VM_BUG_ON(!pmd_none(*new_pmd));
- set_pmd_at(mm, new_addr, new_pmd, pmd);
- spin_unlock(&mm->page_table_lock);
- ret = 1;
- }
- } else {
+ ret = __pmd_trans_huge_lock(old_pmd, vma);
+ if (ret == 1) {
+ pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
+ VM_BUG_ON(!pmd_none(*new_pmd));
+ set_pmd_at(mm, new_addr, new_pmd, pmd);
spin_unlock(&mm->page_table_lock);
}
out:
@@ -1136,26 +1112,43 @@
struct mm_struct *mm = vma->vm_mm;
int ret = 0;
- spin_lock(&mm->page_table_lock);
- if (likely(pmd_trans_huge(*pmd))) {
- if (unlikely(pmd_trans_splitting(*pmd))) {
- spin_unlock(&mm->page_table_lock);
- wait_split_huge_page(vma->anon_vma, pmd);
- } else {
- pmd_t entry;
-
- entry = pmdp_get_and_clear(mm, addr, pmd);
- entry = pmd_modify(entry, newprot);
- set_pmd_at(mm, addr, pmd, entry);
- spin_unlock(&vma->vm_mm->page_table_lock);
- ret = 1;
- }
- } else
+ if (__pmd_trans_huge_lock(pmd, vma) == 1) {
+ pmd_t entry;
+ entry = pmdp_get_and_clear(mm, addr, pmd);
+ entry = pmd_modify(entry, newprot);
+ set_pmd_at(mm, addr, pmd, entry);
spin_unlock(&vma->vm_mm->page_table_lock);
+ ret = 1;
+ }
return ret;
}
+/*
+ * Returns 1 if a given pmd maps a stable (not under splitting) thp.
+ * Returns -1 if it maps a thp under splitting. Returns 0 otherwise.
+ *
+ * Note that if it returns 1, this routine returns without unlocking page
+ * table locks. So callers must unlock them.
+ */
+int __pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
+{
+ spin_lock(&vma->vm_mm->page_table_lock);
+ if (likely(pmd_trans_huge(*pmd))) {
+ if (unlikely(pmd_trans_splitting(*pmd))) {
+ spin_unlock(&vma->vm_mm->page_table_lock);
+ wait_split_huge_page(vma->anon_vma, pmd);
+ return -1;
+ } else {
+ /* Thp mapped by 'pmd' is stable, so we can
+ * handle it as it is. */
+ return 1;
+ }
+ }
+ spin_unlock(&vma->vm_mm->page_table_lock);
+ return 0;
+}
+
pmd_t *page_check_address_pmd(struct page *page,
struct mm_struct *mm,
unsigned long address,