[PATCH 02/14] page-replace-try_pageout.patch

[Peter Zijlstra]

From: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>

Move the functionality of the shrink_list() loop into its own function.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>

 mm/vmscan.c |  324 ++++++++++++++++++++++++++++++++----------------------------
 1 file changed, 174 insertions(+), 150 deletions(-)

Index: linux-2.6-git/mm/vmscan.c
===================================================================
--- linux-2.6-git.orig/mm/vmscan.c
+++ linux-2.6-git/mm/vmscan.c
@@ -51,6 +51,16 @@ typedef enum {
 	PAGE_CLEAN,
 } pageout_t;
 
+/* possible outcome of try_pageout() */
+typedef enum {
+	/* unable to perform pageout */
+	PAGEOUT_KEEP,
+	/* unable to perform pageout, page is in active use */
+	PAGEOUT_ACTIVATE,
+	/* pageout succeded, page is gone */
+	PAGEOUT_SUCCESS,
+} try_pageout_t;
+
 struct scan_control {
 	/* Ask refill_inactive_zone, or shrink_cache to scan this many pages */
 	unsigned long nr_to_scan;
@@ -382,189 +392,203 @@ static pageout_t pageout(struct page *pa
 	return PAGE_CLEAN;
 }
 
-/*
- * shrink_list adds the number of reclaimed pages to sc->nr_reclaimed
- */
-static int shrink_list(struct list_head *page_list, struct scan_control *sc)
+static try_pageout_t try_pageout(struct page *page, struct scan_control *sc)
 {
-	LIST_HEAD(ret_pages);
-	struct pagevec freed_pvec;
-	int pgactivate = 0;
-	int reclaimed = 0;
-
-	cond_resched();
-
-	pagevec_init(&freed_pvec, 1);
-	while (!list_empty(page_list)) {
-		struct address_space *mapping;
-		struct page *page;
-		int may_enter_fs;
-		int referenced;
-
-		cond_resched();
-
-		page = lru_to_page(page_list);
-		list_del(&page->lru);
+	struct address_space *mapping;
+	int may_enter_fs;
+	int referenced;
 
-		if (TestSetPageLocked(page))
-			goto keep;
+	if (TestSetPageLocked(page))
+		goto keep;
 
-		BUG_ON(PageActive(page));
+	BUG_ON(PageActive(page));
 
+	sc->nr_scanned++;
+	/* Double the slab pressure for mapped and swapcache pages */
+	if (page_mapped(page) || PageSwapCache(page))
 		sc->nr_scanned++;
-		/* Double the slab pressure for mapped and swapcache pages */
-		if (page_mapped(page) || PageSwapCache(page))
-			sc->nr_scanned++;
 
-		if (PageWriteback(page))
-			goto keep_locked;
+	if (PageWriteback(page))
+		goto keep_locked;
 
-		referenced = page_referenced(page, 1);
-		/* In active use or really unfreeable?  Activate it. */
-		if (referenced && page_mapping_inuse(page))
-			goto activate_locked;
+	referenced = page_referenced(page, 1);
+	/* In active use or really unfreeable?  Activate it. */
+	if (referenced && page_mapping_inuse(page))
+		goto activate_locked;
 
 #ifdef CONFIG_SWAP
-		/*
-		 * Anonymous process memory has backing store?
-		 * Try to allocate it some swap space here.
-		 */
-		if (PageAnon(page) && !PageSwapCache(page)) {
-			if (!sc->may_swap)
-				goto keep_locked;
-			if (!add_to_swap(page))
-				goto activate_locked;
-		}
+	/*
+	 * Anonymous process memory has backing store?
+	 * Try to allocate it some swap space here.
+	 */
+	if (PageAnon(page) && !PageSwapCache(page)) {
+		if (!sc->may_swap)
+			goto keep_locked;
+		if (!add_to_swap(page))
+			goto activate_locked;
+	}
 #endif /* CONFIG_SWAP */
 
-		mapping = page_mapping(page);
-		may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
-			(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
+	mapping = page_mapping(page);
+	may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
+		(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
 
-		/*
-		 * The page is mapped into the page tables of one or more
-		 * processes. Try to unmap it here.
-		 */
-		if (page_mapped(page) && mapping) {
-			switch (try_to_unmap(page)) {
-			case SWAP_FAIL:
-				goto activate_locked;
-			case SWAP_AGAIN:
-				goto keep_locked;
-			case SWAP_SUCCESS:
-				; /* try to free the page below */
-			}
+	/*
+	 * The page is mapped into the page tables of one or more
+	 * processes. Try to unmap it here.
+	 */
+	if (page_mapped(page) && mapping) {
+		switch (try_to_unmap(page)) {
+		case SWAP_FAIL:
+			goto activate_locked;
+		case SWAP_AGAIN:
+			goto keep_locked;
+		case SWAP_SUCCESS:
+			; /* try to free the page below */
 		}
+	}
 
-		if (PageDirty(page)) {
-			if (referenced)
-				goto keep_locked;
-			if (!may_enter_fs)
-				goto keep_locked;
-			if (laptop_mode && !sc->may_writepage)
-				goto keep_locked;
+	if (PageDirty(page)) {
+		if (referenced)
+			goto keep_locked;
+		if (!may_enter_fs)
+			goto keep_locked;
+		if (laptop_mode && !sc->may_writepage)
+			goto keep_locked;
 
-			/* Page is dirty, try to write it out here */
-			switch(pageout(page, mapping)) {
-			case PAGE_KEEP:
-				goto keep_locked;
-			case PAGE_ACTIVATE:
-				goto activate_locked;
-			case PAGE_SUCCESS:
-				if (PageWriteback(page) || PageDirty(page))
-					goto keep;
+		/* Page is dirty, try to write it out here */
+		switch(pageout(page, mapping)) {
+		case PAGE_KEEP:
+			goto keep_locked;
+		case PAGE_ACTIVATE:
+			goto activate_locked;
+		case PAGE_SUCCESS:
+			if (PageWriteback(page) || PageDirty(page))
+				goto keep;
 				/*
-				 * A synchronous write - probably a ramdisk.  Go
-				 * ahead and try to reclaim the page.
-				 */
-				if (TestSetPageLocked(page))
-					goto keep;
-				if (PageDirty(page) || PageWriteback(page))
-					goto keep_locked;
-				mapping = page_mapping(page);
-			case PAGE_CLEAN:
-				; /* try to free the page below */
-			}
+				* A synchronous write - probably a ramdisk.  Go
+				* ahead and try to reclaim the page.
+				*/
+			if (TestSetPageLocked(page))
+				goto keep;
+			if (PageDirty(page) || PageWriteback(page))
+				goto keep_locked;
+			mapping = page_mapping(page);
+		case PAGE_CLEAN:
+			; /* try to free the page below */
 		}
+	}
 
-		/*
-		 * If the page has buffers, try to free the buffer mappings
-		 * associated with this page. If we succeed we try to free
-		 * the page as well.
-		 *
-		 * We do this even if the page is PageDirty().
-		 * try_to_release_page() does not perform I/O, but it is
-		 * possible for a page to have PageDirty set, but it is actually
-		 * clean (all its buffers are clean).  This happens if the
-		 * buffers were written out directly, with submit_bh(). ext3
-		 * will do this, as well as the blockdev mapping. 
-		 * try_to_release_page() will discover that cleanness and will
-		 * drop the buffers and mark the page clean - it can be freed.
-		 *
-		 * Rarely, pages can have buffers and no ->mapping.  These are
-		 * the pages which were not successfully invalidated in
-		 * truncate_complete_page().  We try to drop those buffers here
-		 * and if that worked, and the page is no longer mapped into
-		 * process address space (page_count == 1) it can be freed.
-		 * Otherwise, leave the page on the LRU so it is swappable.
-		 */
-		if (PagePrivate(page)) {
-			if (!try_to_release_page(page, sc->gfp_mask))
-				goto activate_locked;
-			if (!mapping && page_count(page) == 1)
-				goto free_it;
-		}
+	/*
+	 * If the page has buffers, try to free the buffer mappings
+	 * associated with this page. If we succeed we try to free
+	 * the page as well.
+	 *
+	 * We do this even if the page is PageDirty().
+	 * try_to_release_page() does not perform I/O, but it is
+	 * possible for a page to have PageDirty set, but it is actually
+	 * clean (all its buffers are clean).  This happens if the
+	 * buffers were written out directly, with submit_bh(). ext3
+	 * will do this, as well as the blockdev mapping.
+	 * try_to_release_page() will discover that cleanness and will
+	 * drop the buffers and mark the page clean - it can be freed.
+	 *
+	 * Rarely, pages can have buffers and no ->mapping.  These are
+	 * the pages which were not successfully invalidated in
+	 * truncate_complete_page().  We try to drop those buffers here
+	 * and if that worked, and the page is no longer mapped into
+	 * process address space (page_count == 1) it can be freed.
+	 * Otherwise, leave the page on the LRU so it is swappable.
+	 */
+	if (PagePrivate(page)) {
+		if (!try_to_release_page(page, sc->gfp_mask))
+			goto activate_locked;
+		if (!mapping && page_count(page) == 1)
+			goto free_it;
+	}
 
-		if (!mapping)
-			goto keep_locked;	/* truncate got there first */
+	if (!mapping)
+		goto keep_locked;	/* truncate got there first */
 
-		write_lock_irq(&mapping->tree_lock);
+	write_lock_irq(&mapping->tree_lock);
 
-		/*
-		 * The non-racy check for busy page.  It is critical to check
-		 * PageDirty _after_ making sure that the page is freeable and
-		 * not in use by anybody. 	(pagecache + us == 2)
-		 */
-		if (unlikely(page_count(page) != 2))
-			goto cannot_free;
-		smp_rmb();
-		if (unlikely(PageDirty(page)))
-			goto cannot_free;
+	/*
+	 * The non-racy check for busy page.  It is critical to check
+	 * PageDirty _after_ making sure that the page is freeable and
+	 * not in use by anybody. 	(pagecache + us == 2)
+	 */
+	if (unlikely(page_count(page) != 2))
+		goto cannot_free;
+	smp_rmb();
+	if (unlikely(PageDirty(page)))
+		goto cannot_free;
 
 #ifdef CONFIG_SWAP
-		if (PageSwapCache(page)) {
-			swp_entry_t swap = { .val = page_private(page) };
-			__delete_from_swap_cache(page);
-			write_unlock_irq(&mapping->tree_lock);
-			swap_free(swap);
-			__put_page(page);	/* The pagecache ref */
-			goto free_it;
-		}
+	if (PageSwapCache(page)) {
+		swp_entry_t swap = { .val = page_private(page) };
+		__delete_from_swap_cache(page);
+		write_unlock_irq(&mapping->tree_lock);
+		swap_free(swap);
+		__put_page(page);	/* The pagecache ref */
+		goto free_it;
+	}
 #endif /* CONFIG_SWAP */
 
-		__remove_from_page_cache(page);
-		write_unlock_irq(&mapping->tree_lock);
-		__put_page(page);
+	__remove_from_page_cache(page);
+	write_unlock_irq(&mapping->tree_lock);
+	__put_page(page);
 
 free_it:
-		unlock_page(page);
-		reclaimed++;
-		if (!pagevec_add(&freed_pvec, page))
-			__pagevec_release_nonlru(&freed_pvec);
-		continue;
+	unlock_page(page);
+	return PAGEOUT_SUCCESS;
 
 cannot_free:
-		write_unlock_irq(&mapping->tree_lock);
-		goto keep_locked;
+	write_unlock_irq(&mapping->tree_lock);
+	goto keep_locked;
 
 activate_locked:
-		SetPageActive(page);
-		pgactivate++;
+	unlock_page(page);
+	return PAGEOUT_ACTIVATE;
 keep_locked:
-		unlock_page(page);
+	unlock_page(page);
 keep:
-		list_add(&page->lru, &ret_pages);
-		BUG_ON(PageLRU(page));
+	return PAGEOUT_KEEP;
+}
+
+static int shrink_list(struct list_head *page_list, struct scan_control *sc)
+{
+	LIST_HEAD(ret_pages);
+	struct pagevec freed_pvec;
+	int pgactivate = 0;
+	int reclaimed = 0;
+
+	cond_resched();
+
+	pagevec_init(&freed_pvec, 1);
+	while (!list_empty(page_list)) {
+		struct page *page;
+
+		cond_resched();
+
+		page = lru_to_page(page_list);
+		list_del(&page->lru);
+
+		switch(try_pageout(page, sc)) {
+		case PAGEOUT_ACTIVATE:
+			SetPageActive(page);
+			pgactivate++;
+			/* fall through */
+		case PAGEOUT_KEEP:
+			list_add(&page->lru, &ret_pages);
+			BUG_ON(PageLRU(page));
+			break;
+
+		case PAGEOUT_SUCCESS:
+			reclaimed++;
+			if (!pagevec_add(&freed_pvec, page))
+				__pagevec_release_nonlru(&freed_pvec);
+			break;
+		}
 	}
 	list_splice(&ret_pages, page_list);
 	if (pagevec_count(&freed_pvec))
-
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