THP: add split tail pages to shrink page list in page reclaim

In page reclaim, huge page is split. split_huge_page() adds tail pages to LRU list. Since we are reclaiming a huge page, it's better we reclaim all subpages of the huge page instead of just the head page. This patch adds split tail pages to shrink page list so the tail pages can be reclaimed soon.

Before this patch, run a swap workload:
thp_fault_alloc 3492
thp_fault_fallback 608
thp_collapse_alloc 6
thp_collapse_alloc_failed 0
thp_split 916

With this patch:
thp_fault_alloc 4085
thp_fault_fallback 16
thp_collapse_alloc 90
thp_collapse_alloc_failed 0
thp_split 1272

fallback allocation is reduced a lot.

Signed-off-by Shaohua Li <[email protected]>

In page reclaim, huge page is split. split_huge_page() adds tail pages to LRU list. Since we are reclaiming a huge page, it's better we reclaim all subpages of the huge page instead of just the head page. This patch adds split tail pages to shrink page list so the tail pages can be reclaimed soon.

Before this patch, run a swap workload:
thp_fault_alloc 3492
thp_fault_fallback 608
thp_collapse_alloc 6
thp_collapse_alloc_failed 0
thp_split 916

With this patch:
thp_fault_alloc 4085
thp_fault_fallback 16
thp_collapse_alloc 90
thp_collapse_alloc_failed 0
thp_split 1272

fallback allocation is reduced a lot.

Signed-off-by Shaohua Li <[email protected]>

---
 include/linux/huge_mm.h |   11 ++++++++++-
 include/linux/swap.h    |    4 ++--
 mm/huge_memory.c        |   14 ++++++++------
 mm/swap.c               |   11 ++++++++---
 mm/swap_state.c         |    4 ++--
 mm/vmscan.c             |    2 +-
 6 files changed, 31 insertions(+), 15 deletions(-)

Index: linux/include/linux/huge_mm.h
===================================================================

include/linux/huge_mm.h +10 -1

@@ -99,7 +99,11 @@ extern int copy_pte_range(struct mm_stru
 extern int handle_pte_fault(struct mm_struct *mm,
 			    struct vm_area_struct *vma, unsigned long address,
 			    pte_t *pte, pmd_t *pmd, unsigned int flags);
-extern int split_huge_page(struct page *page);
+extern int split_huge_page_to_list(struct page *page, struct list_head *list);
+static inline int split_huge_page(struct page *page)
+{
+	return split_huge_page_to_list(page, NULL);
+}
 extern void __split_huge_page_pmd(struct vm_area_struct *vma,
 		unsigned long address, pmd_t *pmd);
 #define split_huge_page_pmd(__vma, __address, __pmd)			\

@@ -186,6 +190,11 @@ extern int do_huge_pmd_numa_page(struct
 #define transparent_hugepage_enabled(__vma) 0
 
 #define transparent_hugepage_flags 0UL
+static inline int
+split_huge_page_to_list(struct page *page, struct list_head *list)
+{
+	return 0;
+}
 static inline int split_huge_page(struct page *page)
 {
 	return 0;

Index: linux/include/linux/swap.h
===================================================================

include/linux/swap.h +2 -2

@@ -236,7 +236,7 @@ extern unsigned long nr_free_pagecache_p
 extern void __lru_cache_add(struct page *, enum lru_list lru);
 extern void lru_cache_add_lru(struct page *, enum lru_list lru);
 extern void lru_add_page_tail(struct page *page, struct page *page_tail,
-			      struct lruvec *lruvec);
+			 struct lruvec *lruvec, struct list_head *head);
 extern void activate_page(struct page *);
 extern void mark_page_accessed(struct page *);
 extern void lru_add_drain(void);

@@ -343,7 +343,7 @@ extern struct address_space swapper_spac
 #define swap_address_space(entry) (&swapper_spaces[swp_type(entry)])
 extern unsigned long total_swapcache_pages(void);
 extern void show_swap_cache_info(void);
-extern int add_to_swap(struct page *);
+extern int add_to_swap(struct page *, struct list_head *list);
 extern int add_to_swap_cache(struct page *, swp_entry_t, gfp_t);
 extern void __delete_from_swap_cache(struct page *);
 extern void delete_from_swap_cache(struct page *);

Index: linux/mm/huge_memory.c
===================================================================

mm/huge_memory.c +8 -6

@@ -1560,7 +1560,8 @@ static int __split_huge_page_splitting(s
 	return ret;
 }
 
-static void __split_huge_page_refcount(struct page *page)
+static void __split_huge_page_refcount(struct page *page,
+				       struct list_head *list)
 {
 	int i;
 	struct zone *zone = page_zone(page);

@@ -1646,7 +1647,7 @@ static void __split_huge_page_refcount(s
 		BUG_ON(!PageDirty(page_tail));
 		BUG_ON(!PageSwapBacked(page_tail));
 
-		lru_add_page_tail(page, page_tail, lruvec);
+		lru_add_page_tail(page, page_tail, lruvec, list);
 	}
 	atomic_sub(tail_count, &page->_count);
 	BUG_ON(atomic_read(&page->_count) <= 0);

@@ -1753,7 +1754,8 @@ static int __split_huge_page_map(struct
 
 /* must be called with anon_vma->root->rwsem held */
 static void __split_huge_page(struct page *page,
-			      struct anon_vma *anon_vma)
+			      struct anon_vma *anon_vma,
+			      struct list_head *list)
 {
 	int mapcount, mapcount2;
 	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);

@@ -1784,7 +1786,7 @@ static void __split_huge_page(struct pag
 		       mapcount, page_mapcount(page));
 	BUG_ON(mapcount != page_mapcount(page));
 
-	__split_huge_page_refcount(page);
+	__split_huge_page_refcount(page, list);
 
 	mapcount2 = 0;
 	anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {

@@ -1799,7 +1801,7 @@ static void __split_huge_page(struct pag
 	BUG_ON(mapcount != mapcount2);
 }
 
-int split_huge_page(struct page *page)
+int split_huge_page_to_list(struct page *page, struct list_head *list)
 {
 	struct anon_vma *anon_vma;
 	int ret = 1;

@@ -1824,7 +1826,7 @@ int split_huge_page(struct page *page)
 		goto out_unlock;
 
 	BUG_ON(!PageSwapBacked(page));
-	__split_huge_page(page, anon_vma);
+	__split_huge_page(page, anon_vma, list);
 	count_vm_event(THP_SPLIT);
 
 	BUG_ON(PageCompound(page));

Index: linux/mm/swap.c
===================================================================

mm/swap.c +8 -3

@@ -737,7 +737,7 @@ EXPORT_SYMBOL(__pagevec_release);
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 /* used by __split_huge_page_refcount() */
 void lru_add_page_tail(struct page *page, struct page *page_tail,
-		       struct lruvec *lruvec)
+		       struct lruvec *lruvec, struct list_head *list)
 {
 	int uninitialized_var(active);
 	enum lru_list lru;

@@ -749,7 +749,8 @@ void lru_add_page_tail(struct page *page
 	VM_BUG_ON(NR_CPUS != 1 &&
 		  !spin_is_locked(&lruvec_zone(lruvec)->lru_lock));
 
-	SetPageLRU(page_tail);
+	if (!list)
+		SetPageLRU(page_tail);
 
 	if (page_evictable(page_tail)) {
 		if (PageActive(page)) {

@@ -767,7 +768,11 @@ void lru_add_page_tail(struct page *page
 
 	if (likely(PageLRU(page)))
 		list_add_tail(&page_tail->lru, &page->lru);
-	else {
+	else if (list) {
+		/* page reclaim is reclaiming a huge page */
+		get_page(page_tail);
+		list_add_tail(&page_tail->lru, list);
+	} else {
 		struct list_head *list_head;
 		/*
 		 * Head page has not yet been counted, as an hpage,

Index: linux/mm/swap_state.c
===================================================================

mm/swap_state.c +2 -2

@@ -160,7 +160,7 @@ void __delete_from_swap_cache(struct pag
  * Allocate swap space for the page and add the page to the
  * swap cache.  Caller needs to hold the page lock. 
  */
-int add_to_swap(struct page *page)
+int add_to_swap(struct page *page, struct list_head *list)
 {
 	swp_entry_t entry;
 	int err;

@@ -173,7 +173,7 @@ int add_to_swap(struct page *page)
 		return 0;
 
 	if (unlikely(PageTransHuge(page)))
-		if (unlikely(split_huge_page(page))) {
+		if (unlikely(split_huge_page_to_list(page, list))) {
 			swapcache_free(entry, NULL);
 			return 0;
 		}

Index: linux/mm/vmscan.c
===================================================================

mm/vmscan.c +1 -2

@@ -780,7 +780,7 @@ static unsigned long shrink_page_list(st
 		if (PageAnon(page) && !PageSwapCache(page)) {
 			if (!(sc->gfp_mask & __GFP_IO))
 				goto keep_locked;
-			if (!add_to_swap(page))
+			if (!add_to_swap(page, page_list))
 				goto activate_locked;
 			may_enter_fs = 1;
 		}
 
--

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Hi Shaohua,

Quoted 12 lines · Shaohua Li

In page reclaim, huge page is split. split_huge_page() adds tail pages to LRU list. Since we are reclaiming a huge page, it's better we reclaim all subpages of the huge page instead of just the head page. This patch adds split tail pages to shrink page list so the tail pages can be reclaimed soon.

Before this patch, run a swap workload:
thp_fault_alloc 3492
thp_fault_fallback 608
thp_collapse_alloc 6
thp_collapse_alloc_failed 0
thp_split 916

Quoted 8 lines

With this patch:
thp_fault_alloc 4085
thp_fault_fallback 16
thp_collapse_alloc 90
thp_collapse_alloc_failed 0
thp_split 1272

fallback allocation is reduced a lot.

What I have a concern is that there is about spatial locality about 2M all pages expecially, THP-always case. But yes, THP already have done it via lru_add_page_tail and yours makes more sense if we really intended it.

But I didn't like passing page_list to split_huge_page, either. Couldn't we do it in isolate_lru_pages in shrink_inactive_list? Maybe, we can add new isolate_mode, ISOLATE_SPLIT_HUGEPAGE. One problem I can see is deadlock of zone->lru_lock so maybe we have to release the lock the work and re-hold it.

Quoted 28 lines · Minchan Kim

Hi Shaohua,

Quoted 12 lines · Shaohua Li

In page reclaim, huge page is split. split_huge_page() adds tail pages to LRU list. Since we are reclaiming a huge page, it's better we reclaim all subpages of the huge page instead of just the head page. This patch adds split tail pages to shrink page list so the tail pages can be reclaimed soon.

Before this patch, run a swap workload:
thp_fault_alloc 3492
thp_fault_fallback 608
thp_collapse_alloc 6
thp_collapse_alloc_failed 0
thp_split 916

Quoted 8 lines

With this patch:
thp_fault_alloc 4085
thp_fault_fallback 16
thp_collapse_alloc 90
thp_collapse_alloc_failed 0
thp_split 1272

fallback allocation is reduced a lot.

What I have a concern is that there is about spatial locality about 2M all pages expecially, THP-always case. But yes, THP already have done it via lru_add_page_tail and yours makes more sense if we really intended it.

Quoted 5 lines

But I didn't like passing page_list to split_huge_page, either. Couldn't we do it in isolate_lru_pages in shrink_inactive_list? Maybe, we can add new isolate_mode, ISOLATE_SPLIT_HUGEPAGE. One problem I can see is deadlock of zone->lru_lock so maybe we have to release the lock the work and re-hold it.

I'd prefer split huge page after page_check_references like what we do now. It's possible we don't want to reclaim (so split) the page at all.

Thanks,
Shaohua

--
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In page reclaim, huge page is split. split_huge_page() adds tail pages to LRU list. Since we are reclaiming a huge page, it's better we reclaim all subpages of the huge page instead of just the head page. This patch adds split tail pages to shrink page list so the tail pages can be reclaimed soon.

Before this patch, run a swap workload:
thp_fault_alloc 3492
thp_fault_fallback 608
thp_collapse_alloc 6
thp_collapse_alloc_failed 0
thp_split 916

With this patch:
thp_fault_alloc 4085
thp_fault_fallback 16
thp_collapse_alloc 90
thp_collapse_alloc_failed 0
thp_split 1272

fallback allocation is reduced a lot.

Signed-off-by Shaohua Li <[email protected]>

In page reclaim, huge page is split. split_huge_page() adds tail pages to LRU list. Since we are reclaiming a huge page, it's better we reclaim all subpages of the huge page instead of just the head page. This patch adds split tail pages to shrink page list so the tail pages can be reclaimed soon.

Before this patch, run a swap workload:
thp_fault_alloc 3492
thp_fault_fallback 608
thp_collapse_alloc 6
thp_collapse_alloc_failed 0
thp_split 916

With this patch:
thp_fault_alloc 4085
thp_fault_fallback 16
thp_collapse_alloc 90
thp_collapse_alloc_failed 0
thp_split 1272

fallback allocation is reduced a lot.

Signed-off-by Shaohua Li <[email protected]>

---

include/linux/huge_mm.h |   11 ++++++++++-
include/linux/swap.h    |    4 ++--
mm/huge_memory.c        |   14 ++++++++------
mm/swap.c               |   11 ++++++++---
mm/swap_state.c         |    4 ++--
mm/vmscan.c             |    2 +-
6 files changed, 31 insertions(+), 15 deletions(-)

Index: linux/include/linux/huge_mm.h
===================================================================

include/linux/huge_mm.h +10 -1

@@ -99,7 +99,11 @@ extern int copy_pte_range(struct mm_stru
 extern int handle_pte_fault(struct mm_struct *mm,
 			    struct vm_area_struct *vma, unsigned long address,
 			    pte_t *pte, pmd_t *pmd, unsigned int flags);
-extern int split_huge_page(struct page *page);
+extern int split_huge_page_to_list(struct page *page, struct list_head *list);
+static inline int split_huge_page(struct page *page)
+{
+	return split_huge_page_to_list(page, NULL);
+}
 extern void __split_huge_page_pmd(struct vm_area_struct *vma,
 		unsigned long address, pmd_t *pmd);
 #define split_huge_page_pmd(__vma, __address, __pmd)			\

@@ -186,6 +190,11 @@ extern int do_huge_pmd_numa_page(struct
 #define transparent_hugepage_enabled(__vma) 0
 
 #define transparent_hugepage_flags 0UL
+static inline int
+split_huge_page_to_list(struct page *page, struct list_head *list)
+{
+	return 0;
+}
 static inline int split_huge_page(struct page *page)
 {
 	return 0;

Index: linux/include/linux/swap.h
===================================================================

include/linux/swap.h +2 -2

@@ -236,7 +236,7 @@ extern unsigned long nr_free_pagecache_p
 extern void __lru_cache_add(struct page *, enum lru_list lru);
 extern void lru_cache_add_lru(struct page *, enum lru_list lru);
 extern void lru_add_page_tail(struct page *page, struct page *page_tail,
-			      struct lruvec *lruvec);
+			 struct lruvec *lruvec, struct list_head *head);
 extern void activate_page(struct page *);
 extern void mark_page_accessed(struct page *);
 extern void lru_add_drain(void);

@@ -343,7 +343,7 @@ extern struct address_space swapper_spac
 #define swap_address_space(entry) (&swapper_spaces[swp_type(entry)])
 extern unsigned long total_swapcache_pages(void);
 extern void show_swap_cache_info(void);
-extern int add_to_swap(struct page *);
+extern int add_to_swap(struct page *, struct list_head *list);
 extern int add_to_swap_cache(struct page *, swp_entry_t, gfp_t);
 extern void __delete_from_swap_cache(struct page *);
 extern void delete_from_swap_cache(struct page *);

Index: linux/mm/huge_memory.c
===================================================================

mm/huge_memory.c +8 -6

@@ -1560,7 +1560,8 @@ static int __split_huge_page_splitting(s
 	return ret;
 }
 
-static void __split_huge_page_refcount(struct page *page)
+static void __split_huge_page_refcount(struct page *page,
+				       struct list_head *list)
 {
 	int i;
 	struct zone *zone = page_zone(page);

@@ -1646,7 +1647,7 @@ static void __split_huge_page_refcount(s
 		BUG_ON(!PageDirty(page_tail));
 		BUG_ON(!PageSwapBacked(page_tail));
 
-		lru_add_page_tail(page, page_tail, lruvec);
+		lru_add_page_tail(page, page_tail, lruvec, list);
 	}
 	atomic_sub(tail_count, &page->_count);
 	BUG_ON(atomic_read(&page->_count) <= 0);

@@ -1753,7 +1754,8 @@ static int __split_huge_page_map(struct
 
 /* must be called with anon_vma->root->rwsem held */
 static void __split_huge_page(struct page *page,
-			      struct anon_vma *anon_vma)
+			      struct anon_vma *anon_vma,
+			      struct list_head *list)
 {
 	int mapcount, mapcount2;
 	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);

@@ -1784,7 +1786,7 @@ static void __split_huge_page(struct pag
 		       mapcount, page_mapcount(page));
 	BUG_ON(mapcount != page_mapcount(page));
 
-	__split_huge_page_refcount(page);
+	__split_huge_page_refcount(page, list);
 
 	mapcount2 = 0;
 	anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {

@@ -1799,7 +1801,7 @@ static void __split_huge_page(struct pag
 	BUG_ON(mapcount != mapcount2);
 }
 
-int split_huge_page(struct page *page)
+int split_huge_page_to_list(struct page *page, struct list_head *list)
 {
 	struct anon_vma *anon_vma;
 	int ret = 1;

@@ -1824,7 +1826,7 @@ int split_huge_page(struct page *page)
 		goto out_unlock;
 
 	BUG_ON(!PageSwapBacked(page));
-	__split_huge_page(page, anon_vma);
+	__split_huge_page(page, anon_vma, list);
 	count_vm_event(THP_SPLIT);
 
 	BUG_ON(PageCompound(page));

Index: linux/mm/swap.c
===================================================================

mm/swap.c +8 -3

@@ -737,7 +737,7 @@ EXPORT_SYMBOL(__pagevec_release);
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 /* used by __split_huge_page_refcount() */
 void lru_add_page_tail(struct page *page, struct page *page_tail,
-		       struct lruvec *lruvec)
+		       struct lruvec *lruvec, struct list_head *list)
 {
 	int uninitialized_var(active);
 	enum lru_list lru;

@@ -749,7 +749,8 @@ void lru_add_page_tail(struct page *page
 	VM_BUG_ON(NR_CPUS != 1 &&
 		  !spin_is_locked(&lruvec_zone(lruvec)->lru_lock));
 
-	SetPageLRU(page_tail);
+	if (!list)
+		SetPageLRU(page_tail);
 
 	if (page_evictable(page_tail)) {
 		if (PageActive(page)) {

@@ -767,7 +768,11 @@ void lru_add_page_tail(struct page *page
 
 	if (likely(PageLRU(page)))
 		list_add_tail(&page_tail->lru, &page->lru);
-	else {
+	else if (list) {
+		/* page reclaim is reclaiming a huge page */
+		get_page(page_tail);
+		list_add_tail(&page_tail->lru, list);
+	} else {
 		struct list_head *list_head;
 		/*
 		 * Head page has not yet been counted, as an hpage,

Index: linux/mm/swap_state.c
===================================================================

mm/swap_state.c +2 -2

@@ -160,7 +160,7 @@ void __delete_from_swap_cache(struct pag
 * Allocate swap space for the page and add the page to the
 * swap cache.  Caller needs to hold the page lock. 
 */
-int add_to_swap(struct page *page)
+int add_to_swap(struct page *page, struct list_head *list)
 {
 	swp_entry_t entry;
 	int err;

@@ -173,7 +173,7 @@ int add_to_swap(struct page *page)
 		return 0;
 
 	if (unlikely(PageTransHuge(page)))
-		if (unlikely(split_huge_page(page))) {
+		if (unlikely(split_huge_page_to_list(page, list))) {
 			swapcache_free(entry, NULL);
 			return 0;
 		}

Index: linux/mm/vmscan.c
===================================================================

mm/vmscan.c +1 -2

@@ -780,7 +780,7 @@ static unsigned long shrink_page_list(st
 		if (PageAnon(page) && !PageSwapCache(page)) {
 			if (!(sc->gfp_mask & __GFP_IO))
 				goto keep_locked;
-			if (!add_to_swap(page))
+			if (!add_to_swap(page, page_list))
 				goto activate_locked;
 			may_enter_fs = 1;
 		}
 
--

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In page reclaim, huge page is split. split_huge_page() adds tail pages to LRU list. Since we are reclaiming a huge page, it's better we reclaim all subpages of the huge page instead of just the head page. This patch adds split tail pages to shrink page list so the tail pages can be reclaimed soon.

Before this patch, run a swap workload:
thp_fault_alloc 3492
thp_fault_fallback 608
thp_collapse_alloc 6
thp_collapse_alloc_failed 0
thp_split 916

With this patch:
thp_fault_alloc 4085
thp_fault_fallback 16
thp_collapse_alloc 90
thp_collapse_alloc_failed 0
thp_split 1272

fallback allocation is reduced a lot.

Signed-off-by Shaohua Li <[email protected]>

---

include/linux/huge_mm.h |   11 ++++++++++-
include/linux/swap.h    |    4 ++--
mm/huge_memory.c        |   14 ++++++++------
mm/swap.c               |   11 ++++++++---
mm/swap_state.c         |    4 ++--
mm/vmscan.c             |    2 +-
6 files changed, 31 insertions(+), 15 deletions(-)

Index: linux/include/linux/huge_mm.h
===================================================================

include/linux/huge_mm.h +10 -1

@@ -99,7 +99,11 @@ extern int copy_pte_range(struct mm_stru
 extern int handle_pte_fault(struct mm_struct *mm,
 			    struct vm_area_struct *vma, unsigned long address,
 			    pte_t *pte, pmd_t *pmd, unsigned int flags);
-extern int split_huge_page(struct page *page);
+extern int split_huge_page_to_list(struct page *page, struct list_head *list);
+static inline int split_huge_page(struct page *page)
+{
+	return split_huge_page_to_list(page, NULL);
+}
 extern void __split_huge_page_pmd(struct vm_area_struct *vma,
 		unsigned long address, pmd_t *pmd);
 #define split_huge_page_pmd(__vma, __address, __pmd)			\

@@ -186,6 +190,11 @@ extern int do_huge_pmd_numa_page(struct
 #define transparent_hugepage_enabled(__vma) 0
 
 #define transparent_hugepage_flags 0UL
+static inline int
+split_huge_page_to_list(struct page *page, struct list_head *list)
+{
+	return 0;
+}
 static inline int split_huge_page(struct page *page)
 {
 	return 0;

Index: linux/include/linux/swap.h
===================================================================

include/linux/swap.h +2 -2

@@ -236,7 +236,7 @@ extern unsigned long nr_free_pagecache_p
 extern void __lru_cache_add(struct page *, enum lru_list lru);
 extern void lru_cache_add_lru(struct page *, enum lru_list lru);
 extern void lru_add_page_tail(struct page *page, struct page *page_tail,
-			      struct lruvec *lruvec);
+			 struct lruvec *lruvec, struct list_head *head);
 extern void activate_page(struct page *);
 extern void mark_page_accessed(struct page *);
 extern void lru_add_drain(void);

@@ -343,7 +343,7 @@ extern struct address_space swapper_spac
 #define swap_address_space(entry) (&swapper_spaces[swp_type(entry)])
 extern unsigned long total_swapcache_pages(void);
 extern void show_swap_cache_info(void);
-extern int add_to_swap(struct page *);
+extern int add_to_swap(struct page *, struct list_head *list);
 extern int add_to_swap_cache(struct page *, swp_entry_t, gfp_t);
 extern void __delete_from_swap_cache(struct page *);
 extern void delete_from_swap_cache(struct page *);

Index: linux/mm/huge_memory.c
===================================================================

mm/huge_memory.c +8 -6

@@ -1560,7 +1560,8 @@ static int __split_huge_page_splitting(s
 	return ret;
 }
 
-static void __split_huge_page_refcount(struct page *page)
+static void __split_huge_page_refcount(struct page *page,
+				       struct list_head *list)
 {
 	int i;
 	struct zone *zone = page_zone(page);

@@ -1646,7 +1647,7 @@ static void __split_huge_page_refcount(s
 		BUG_ON(!PageDirty(page_tail));
 		BUG_ON(!PageSwapBacked(page_tail));
 
-		lru_add_page_tail(page, page_tail, lruvec);
+		lru_add_page_tail(page, page_tail, lruvec, list);
 	}
 	atomic_sub(tail_count, &page->_count);
 	BUG_ON(atomic_read(&page->_count) <= 0);

@@ -1753,7 +1754,8 @@ static int __split_huge_page_map(struct
 
 /* must be called with anon_vma->root->rwsem held */
 static void __split_huge_page(struct page *page,
-			      struct anon_vma *anon_vma)
+			      struct anon_vma *anon_vma,
+			      struct list_head *list)
 {
 	int mapcount, mapcount2;
 	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);

@@ -1784,7 +1786,7 @@ static void __split_huge_page(struct pag
 		       mapcount, page_mapcount(page));
 	BUG_ON(mapcount != page_mapcount(page));
 
-	__split_huge_page_refcount(page);
+	__split_huge_page_refcount(page, list);
 
 	mapcount2 = 0;
 	anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {

@@ -1799,7 +1801,7 @@ static void __split_huge_page(struct pag
 	BUG_ON(mapcount != mapcount2);
 }
 
-int split_huge_page(struct page *page)
+int split_huge_page_to_list(struct page *page, struct list_head *list)
 {
 	struct anon_vma *anon_vma;
 	int ret = 1;

@@ -1824,7 +1826,7 @@ int split_huge_page(struct page *page)
 		goto out_unlock;
 
 	BUG_ON(!PageSwapBacked(page));
-	__split_huge_page(page, anon_vma);
+	__split_huge_page(page, anon_vma, list);
 	count_vm_event(THP_SPLIT);
 
 	BUG_ON(PageCompound(page));

Index: linux/mm/swap.c
===================================================================

mm/swap.c +8 -3

@@ -737,7 +737,7 @@ EXPORT_SYMBOL(__pagevec_release);
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 /* used by __split_huge_page_refcount() */
 void lru_add_page_tail(struct page *page, struct page *page_tail,
-		       struct lruvec *lruvec)
+		       struct lruvec *lruvec, struct list_head *list)
 {
 	int uninitialized_var(active);
 	enum lru_list lru;

@@ -749,7 +749,8 @@ void lru_add_page_tail(struct page *page
 	VM_BUG_ON(NR_CPUS != 1 &&
 		  !spin_is_locked(&lruvec_zone(lruvec)->lru_lock));
 
-	SetPageLRU(page_tail);
+	if (!list)
+		SetPageLRU(page_tail);
 
 	if (page_evictable(page_tail)) {
 		if (PageActive(page)) {

@@ -767,7 +768,11 @@ void lru_add_page_tail(struct page *page
 
 	if (likely(PageLRU(page)))
 		list_add_tail(&page_tail->lru, &page->lru);
-	else {
+	else if (list) {
+		/* page reclaim is reclaiming a huge page */
+		get_page(page_tail);
+		list_add_tail(&page_tail->lru, list);
+	} else {
 		struct list_head *list_head;
 		/*
 		 * Head page has not yet been counted, as an hpage,

Index: linux/mm/swap_state.c
===================================================================

mm/swap_state.c +2 -2

@@ -160,7 +160,7 @@ void __delete_from_swap_cache(struct pag
 * Allocate swap space for the page and add the page to the
 * swap cache.  Caller needs to hold the page lock. 
 */
-int add_to_swap(struct page *page)
+int add_to_swap(struct page *page, struct list_head *list)
 {
 	swp_entry_t entry;
 	int err;

@@ -173,7 +173,7 @@ int add_to_swap(struct page *page)
 		return 0;
 
 	if (unlikely(PageTransHuge(page)))
-		if (unlikely(split_huge_page(page))) {
+		if (unlikely(split_huge_page_to_list(page, list))) {
 			swapcache_free(entry, NULL);
 			return 0;
 		}

Index: linux/mm/vmscan.c
===================================================================

mm/vmscan.c +1 -2

@@ -780,7 +780,7 @@ static unsigned long shrink_page_list(st
 		if (PageAnon(page) && !PageSwapCache(page)) {
 			if (!(sc->gfp_mask & __GFP_IO))
 				goto keep_locked;
-			if (!add_to_swap(page))
+			if (!add_to_swap(page, page_list))
 				goto activate_locked;
 			may_enter_fs = 1;
 		}
 
--

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In page reclaim, huge page is split. split_huge_page() adds tail pages to LRU list. Since we are reclaiming a huge page, it's better we reclaim all subpages of the huge page instead of just the head page. This patch adds split tail pages to shrink page list so the tail pages can be reclaimed soon.

Before this patch, run a swap workload:
thp_fault_alloc 3492
thp_fault_fallback 608
thp_collapse_alloc 6
thp_collapse_alloc_failed 0
thp_split 916

With this patch:
thp_fault_alloc 4085
thp_fault_fallback 16
thp_collapse_alloc 90
thp_collapse_alloc_failed 0
thp_split 1272

fallback allocation is reduced a lot.

...

Quoted 21 lines · On Mon, 1 Apr 2013 21:26:05 +0800 Shaohua Li <[email protected]> wrote:

In page reclaim, huge page is split. split_huge_page() adds tail pages to LRU list. Since we are reclaiming a huge page, it's better we reclaim all subpages of the huge page instead of just the head page. This patch adds split tail pages to shrink page list so the tail pages can be reclaimed soon.

Before this patch, run a swap workload:
thp_fault_alloc 3492
thp_fault_fallback 608
thp_collapse_alloc 6
thp_collapse_alloc_failed 0
thp_split 916

With this patch:
thp_fault_alloc 4085
thp_fault_fallback 16
thp_collapse_alloc 90
thp_collapse_alloc_failed 0
thp_split 1272

fallback allocation is reduced a lot.

Review

Quoted 4 lines

...

(quoted diff) +1 -1

-int split_huge_page(struct page *page)
+int split_huge_page_to_list(struct page *page, struct list_head *list)

While it's fresh, could you please prepare a covering comment describing this function? The meaning of the return value is particularly cryptic.