[PATCH] mm: use-once cleanup

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

Hi,

This is yet another implementation of the PG_useonce cleanup spoken of
during the VM summit.

The idea is to mark a page PG_useonce on pagecache entry and modify the
page_referenced() check to retry on the inactive list instead of
promotion to the active list when PG_useonce is set. PG_useonce is
cleared on first use.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 include/linux/mm_inline.h  |    2 ++
 include/linux/page-flags.h |    5 +++++
 mm/filemap.c               |   22 +++++++++++++---------
 mm/page_alloc.c            |    9 ++++++---
 mm/shmem.c                 |    7 ++-----
 mm/swap.c                  |   11 ++---------
 mm/vmscan.c                |   36 +++++++++++-------------------------
 7 files changed, 41 insertions(+), 51 deletions(-)

Index: linux-2.6/include/linux/mm_inline.h
===================================================================
--- linux-2.6.orig/include/linux/mm_inline.h	2006-07-17 22:31:06.000000000 +0200
+++ linux-2.6/include/linux/mm_inline.h	2006-07-17 22:35:32.000000000 +0200
@@ -37,5 +37,7 @@ del_page_from_lru(struct zone *zone, str
 	} else {
 		zone->nr_inactive--;
 	}
+	if (PageUseOnce(page))
+		ClearPageUseOnce(page);
 }
 
Index: linux-2.6/include/linux/page-flags.h
===================================================================
--- linux-2.6.orig/include/linux/page-flags.h	2006-07-17 22:31:09.000000000 +0200
+++ linux-2.6/include/linux/page-flags.h	2006-07-17 22:39:14.000000000 +0200
@@ -86,6 +86,7 @@
 #define PG_nosave_free		18	/* Free, should not be written */
 #define PG_buddy		19	/* Page is free, on buddy lists */
 
+#define PG_useonce		20	/* Page is new to the pagecache */
 
 #if (BITS_PER_LONG > 32)
 /*
@@ -247,6 +248,10 @@
 #define SetPageUncached(page)	set_bit(PG_uncached, &(page)->flags)
 #define ClearPageUncached(page)	clear_bit(PG_uncached, &(page)->flags)
 
+#define PageUseOnce(page)	test_bit(PG_useonce, &(page)->flags)
+#define SetPageUseOnce(page)	set_bit(PG_useonce, &(page)->flags)
+#define ClearPageUseOnce(page)	clear_bit(PG_useonce, &(page)->flags)
+
 struct page;	/* forward declaration */
 
 int test_clear_page_dirty(struct page *page);
Index: linux-2.6/mm/filemap.c
===================================================================
--- linux-2.6.orig/mm/filemap.c	2006-07-17 22:31:17.000000000 +0200
+++ linux-2.6/mm/filemap.c	2006-07-17 22:35:32.000000000 +0200
@@ -444,6 +444,18 @@ int add_to_page_cache(struct page *page,
 		error = radix_tree_insert(&mapping->page_tree, offset, page);
 		if (!error) {
 			page_cache_get(page);
+			/*
+			 * shmem_getpage()
+			 *   lookup_swap_cache()
+			 *   TestSetPageLocked()
+			 *   move_from_swap_cache()
+			 *     add_to_page_cache()
+			 *
+			 * That path calls us with a LRU page instead of a new
+			 * page. Don't set the hint for LRU pages.
+			 */
+			if (!PageLocked(page))
+				SetPageUseOnce(page);
 			SetPageLocked(page);
 			page->mapping = mapping;
 			page->index = offset;
@@ -884,7 +896,6 @@ void do_generic_mapping_read(struct addr
 	unsigned long offset;
 	unsigned long last_index;
 	unsigned long next_index;
-	unsigned long prev_index;
 	loff_t isize;
 	struct page *cached_page;
 	int error;
@@ -893,7 +904,6 @@ void do_generic_mapping_read(struct addr
 	cached_page = NULL;
 	index = *ppos >> PAGE_CACHE_SHIFT;
 	next_index = index;
-	prev_index = ra.prev_page;
 	last_index = (*ppos + desc->count + PAGE_CACHE_SIZE-1) >> PAGE_CACHE_SHIFT;
 	offset = *ppos & ~PAGE_CACHE_MASK;
 
@@ -940,13 +950,7 @@ page_ok:
 		if (mapping_writably_mapped(mapping))
 			flush_dcache_page(page);
 
-		/*
-		 * When (part of) the same page is read multiple times
-		 * in succession, only mark it as accessed the first time.
-		 */
-		if (prev_index != index)
-			mark_page_accessed(page);
-		prev_index = index;
+		mark_page_accessed(page);
 
 		/*
 		 * Ok, we have the page, and it's up-to-date, so
Index: linux-2.6/mm/page_alloc.c
===================================================================
--- linux-2.6.orig/mm/page_alloc.c	2006-07-17 22:31:17.000000000 +0200
+++ linux-2.6/mm/page_alloc.c	2006-07-17 22:38:25.000000000 +0200
@@ -154,7 +154,8 @@ static void bad_page(struct page *page)
 			1 << PG_slab    |
 			1 << PG_swapcache |
 			1 << PG_writeback |
-			1 << PG_buddy );
+			1 << PG_buddy |
+			1 << PG_useonce);
 	set_page_count(page, 0);
 	reset_page_mapcount(page);
 	page->mapping = NULL;
@@ -389,7 +390,8 @@ static inline int free_pages_check(struc
 			1 << PG_swapcache |
 			1 << PG_writeback |
 			1 << PG_reserved |
-			1 << PG_buddy ))))
+			1 << PG_buddy |
+			1 << PF_useonce ))))
 		bad_page(page);
 	if (PageDirty(page))
 		__ClearPageDirty(page);
@@ -538,7 +540,8 @@ static int prep_new_page(struct page *pa
 			1 << PG_swapcache |
 			1 << PG_writeback |
 			1 << PG_reserved |
-			1 << PG_buddy ))))
+			1 << PG_buddy |
+			1 << PG_useonce ))))
 		bad_page(page);
 
 	/*
Index: linux-2.6/mm/shmem.c
===================================================================
--- linux-2.6.orig/mm/shmem.c	2006-07-17 22:31:17.000000000 +0200
+++ linux-2.6/mm/shmem.c	2006-07-17 22:35:32.000000000 +0200
@@ -1567,11 +1567,8 @@ static void do_shmem_file_read(struct fi
 			 */
 			if (mapping_writably_mapped(mapping))
 				flush_dcache_page(page);
-			/*
-			 * Mark the page accessed if we read the beginning.
-			 */
-			if (!offset)
-				mark_page_accessed(page);
+
+			mark_page_accessed(page);
 		} else {
 			page = ZERO_PAGE(0);
 			page_cache_get(page);
Index: linux-2.6/mm/swap.c
===================================================================
--- linux-2.6.orig/mm/swap.c	2006-07-17 22:31:18.000000000 +0200
+++ linux-2.6/mm/swap.c	2006-07-17 22:35:32.000000000 +0200
@@ -114,19 +114,11 @@ void fastcall activate_page(struct page 
 
 /*
  * Mark a page as having seen activity.
- *
- * inactive,unreferenced	->	inactive,referenced
- * inactive,referenced		->	active,unreferenced
- * active,unreferenced		->	active,referenced
  */
 void fastcall mark_page_accessed(struct page *page)
 {
-	if (!PageActive(page) && PageReferenced(page) && PageLRU(page)) {
-		activate_page(page);
-		ClearPageReferenced(page);
-	} else if (!PageReferenced(page)) {
+	if (!PageReferenced(page))
 		SetPageReferenced(page);
-	}
 }
 
 EXPORT_SYMBOL(mark_page_accessed);
@@ -153,6 +145,7 @@ void fastcall lru_cache_add_active(struc
 	struct pagevec *pvec = &get_cpu_var(lru_add_active_pvecs);
 
 	page_cache_get(page);
+	ClearPageUseOnce(page);
 	if (!pagevec_add(pvec, page))
 		__pagevec_lru_add_active(pvec);
 	put_cpu_var(lru_add_active_pvecs);
Index: linux-2.6/mm/vmscan.c
===================================================================
--- linux-2.6.orig/mm/vmscan.c	2006-07-17 22:31:18.000000000 +0200
+++ linux-2.6/mm/vmscan.c	2006-07-17 22:35:32.000000000 +0200
@@ -227,27 +227,6 @@ unsigned long shrink_slab(unsigned long 
 	return ret;
 }
 
-/* Called without lock on whether page is mapped, so answer is unstable */
-static inline int page_mapping_inuse(struct page *page)
-{
-	struct address_space *mapping;
-
-	/* Page is in somebody's page tables. */
-	if (page_mapped(page))
-		return 1;
-
-	/* Be more reluctant to reclaim swapcache than pagecache */
-	if (PageSwapCache(page))
-		return 1;
-
-	mapping = page_mapping(page);
-	if (!mapping)
-		return 0;
-
-	/* File is mmap'd by somebody? */
-	return mapping_mapped(mapping);
-}
-
 static inline int is_page_cache_freeable(struct page *page)
 {
 	return page_count(page) - !!PagePrivate(page) == 2;
@@ -456,8 +435,13 @@ static unsigned long shrink_page_list(st
 
 		referenced = page_referenced(page, 1);
 		/* In active use or really unfreeable?  Activate it. */
-		if (referenced && page_mapping_inuse(page))
+		if (referenced) {
+			if (PageUseOnce(page)) {
+				ClearPageUseOnce(page);
+				goto keep_locked;
+			}
 			goto activate_locked;
+		}
 
 #ifdef CONFIG_SWAP
 		/*
@@ -551,6 +535,7 @@ static unsigned long shrink_page_list(st
 			goto keep_locked;
 
 free_it:
+		ClearPageUseOnce(page);
 		unlock_page(page);
 		nr_reclaimed++;
 		if (!pagevec_add(&freed_pvec, page))
@@ -724,6 +709,7 @@ static void shrink_active_list(unsigned 
 	struct page *page;
 	struct pagevec pvec;
 	int reclaim_mapped = 0;
+	int referenced;
 
 	if (sc->may_swap) {
 		long mapped_ratio;
@@ -780,10 +766,10 @@ static void shrink_active_list(unsigned 
 		cond_resched();
 		page = lru_to_page(&l_hold);
 		list_del(&page->lru);
+		referenced = page_referenced(page, 0);
 		if (page_mapped(page)) {
-			if (!reclaim_mapped ||
-			    (total_swap_pages == 0 && PageAnon(page)) ||
-			    page_referenced(page, 0)) {
+			if (referenced || !reclaim_mapped ||
+			    (total_swap_pages == 0 && PageAnon(page))) {
 				list_add(&page->lru, &l_active);
 				continue;
 			}


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