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>

1 files changed, 25 insertions, 48 deletions

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 95264c0ef308..328843de6e9f 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -394,20 +394,11 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
         pte_t *pte;
         spinlock_t *ptl;
 
-        spin_lock(&walk->mm->page_table_lock);
-        if (pmd_trans_huge(*pmd)) {
-                if (pmd_trans_splitting(*pmd)) {
-                        spin_unlock(&walk->mm->page_table_lock);
-                        wait_split_huge_page(vma->anon_vma, pmd);
-                } else {
-                        smaps_pte_entry(*(pte_t *)pmd, addr,
-                                        HPAGE_PMD_SIZE, walk);
-                        spin_unlock(&walk->mm->page_table_lock);
-                        mss->anonymous_thp += HPAGE_PMD_SIZE;
-                        return 0;
-                }
-        } else {
+        if (pmd_trans_huge_lock(pmd, vma) == 1) {
+                smaps_pte_entry(*(pte_t *)pmd, addr, HPAGE_PMD_SIZE, walk);
                 spin_unlock(&walk->mm->page_table_lock);
+                mss->anonymous_thp += HPAGE_PMD_SIZE;
+                return 0;
         }
 
         if (pmd_trans_unstable(pmd))
@@ -705,26 +696,19 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
         /* find the first VMA at or above 'addr' */
         vma = find_vma(walk->mm, addr);
         spin_lock(&walk->mm->page_table_lock);
-        if (pmd_trans_huge(*pmd)) {
-                if (pmd_trans_splitting(*pmd)) {
-                        spin_unlock(&walk->mm->page_table_lock);
-                        wait_split_huge_page(vma->anon_vma, pmd);
-                } else {
-                        for (; addr != end; addr += PAGE_SIZE) {
-                                unsigned long offset;
-
-                                offset = (addr & ~PAGEMAP_WALK_MASK) >>
-                                                PAGE_SHIFT;
-                                pfn = thp_pmd_to_pagemap_entry(*pmd, offset);
-                                err = add_to_pagemap(addr, pfn, pm);
-                                if (err)
-                                        break;
-                        }
-                        spin_unlock(&walk->mm->page_table_lock);
-                        return err;
+        if (pmd_trans_huge_lock(pmd, vma) == 1) {
+                for (; addr != end; addr += PAGE_SIZE) {
+                        unsigned long offset;
+
+                        offset = (addr & ~PAGEMAP_WALK_MASK) >>
+                                        PAGE_SHIFT;
+                        pfn = thp_pmd_to_pagemap_entry(*pmd, offset);
+                        err = add_to_pagemap(addr, pfn, pm);
+                        if (err)
+                                break;
                 }
-        } else {
                 spin_unlock(&walk->mm->page_table_lock);
+                return err;
         }
 
         for (; addr != end; addr += PAGE_SIZE) {
@@ -992,24 +976,17 @@ static int gather_pte_stats(pmd_t *pmd, unsigned long addr,
         pte_t *pte;
 
         md = walk->private;
-        spin_lock(&walk->mm->page_table_lock);
-        if (pmd_trans_huge(*pmd)) {
-                if (pmd_trans_splitting(*pmd)) {
-                        spin_unlock(&walk->mm->page_table_lock);
-                        wait_split_huge_page(md->vma->anon_vma, pmd);
-                } else {
-                        pte_t huge_pte = *(pte_t *)pmd;
-                        struct page *page;
-
-                        page = can_gather_numa_stats(huge_pte, md->vma, addr);
-                        if (page)
-                                gather_stats(page, md, pte_dirty(huge_pte),
-                                                HPAGE_PMD_SIZE/PAGE_SIZE);
-                        spin_unlock(&walk->mm->page_table_lock);
-                        return 0;
-                }
-        } else {
+
+        if (pmd_trans_huge_lock(pmd, md->vma) == 1) {
+                pte_t huge_pte = *(pte_t *)pmd;
+                struct page *page;
+
+                page = can_gather_numa_stats(huge_pte, md->vma, addr);
+                if (page)
+                        gather_stats(page, md, pte_dirty(huge_pte),
+                                     HPAGE_PMD_SIZE/PAGE_SIZE);
                 spin_unlock(&walk->mm->page_table_lock);
+                return 0;
         }
 
         if (pmd_trans_unstable(pmd))