6 files changed, 100 insertions, 34 deletions

diff --git a/fs/9p/cache.c b/fs/9p/cache.c
index 51c94e26a34..bcc5357a906 100644
--- a/fs/9p/cache.c
+++ b/fs/9p/cache.c
@@ -343,18 +343,7 @@ int __v9fs_fscache_release_page(struct page *page, gfp_t gfp)
 
 	BUG_ON(!vcookie->fscache);
 
-	if (PageFsCache(page)) {
-		if (fscache_check_page_write(vcookie->fscache, page)) {
-			if (!(gfp & __GFP_WAIT))
-				return 0;
-			fscache_wait_on_page_write(vcookie->fscache, page);
-		}
-
-		fscache_uncache_page(vcookie->fscache, page);
-		ClearPageFsCache(page);
-	}
-
-	return 1;
+	return fscache_maybe_release_page(vnode->cache, page, gfp);
 }
 
 void __v9fs_fscache_invalidate_page(struct page *page)
@@ -368,7 +357,6 @@ void __v9fs_fscache_invalidate_page(struct page *page)
 		fscache_wait_on_page_write(vcookie->fscache, page);
 		BUG_ON(!PageLocked(page));
 		fscache_uncache_page(vcookie->fscache, page);
-		ClearPageFsCache(page);
 	}
 }
 
diff --git a/fs/afs/file.c b/fs/afs/file.c
index 681c2a7b013..39b301662f2 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -315,7 +315,6 @@ static void afs_invalidatepage(struct page *page, unsigned long offset)
 			struct afs_vnode *vnode = AFS_FS_I(page->mapping->host);
 			fscache_wait_on_page_write(vnode->cache, page);
 			fscache_uncache_page(vnode->cache, page);
-			ClearPageFsCache(page);
 		}
 #endif
 
@@ -349,17 +348,9 @@ static int afs_releasepage(struct page *page, gfp_t gfp_flags)
 	/* deny if page is being written to the cache and the caller hasn't
 	 * elected to wait */
 #ifdef CONFIG_AFS_FSCACHE
-	if (PageFsCache(page)) {
-		if (fscache_check_page_write(vnode->cache, page)) {
-			if (!(gfp_flags & __GFP_WAIT)) {
-				_leave(" = F [cache busy]");
-				return 0;
-			}
-			fscache_wait_on_page_write(vnode->cache, page);
-		}
-
-		fscache_uncache_page(vnode->cache, page);
-		ClearPageFsCache(page);
+	if (!fscache_maybe_release_page(vnode->cache, page, gfp_flags)) {
+		_leave(" = F [cache busy]");
+		return 0;
 	}
 #endif
 
diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h
index a0769872b19..e5046519b15 100644
--- a/fs/fscache/internal.h
+++ b/fs/fscache/internal.h
@@ -180,6 +180,11 @@ extern atomic_t fscache_n_store_pages;
 extern atomic_t fscache_n_store_radix_deletes;
 extern atomic_t fscache_n_store_pages_over_limit;
 
+extern atomic_t fscache_n_store_vmscan_not_storing;
+extern atomic_t fscache_n_store_vmscan_gone;
+extern atomic_t fscache_n_store_vmscan_busy;
+extern atomic_t fscache_n_store_vmscan_cancelled;
+
 extern atomic_t fscache_n_marks;
 extern atomic_t fscache_n_uncaches;
 
diff --git a/fs/fscache/page.c b/fs/fscache/page.c
index 022a5da8e13..fc76798bd96 100644
--- a/fs/fscache/page.c
+++ b/fs/fscache/page.c
@@ -43,6 +43,75 @@ void __fscache_wait_on_page_write(struct fscache_cookie *cookie, struct page *pa
 EXPORT_SYMBOL(__fscache_wait_on_page_write);
 
 /*
+ * decide whether a page can be released, possibly by cancelling a store to it
+ * - we're allowed to sleep if __GFP_WAIT is flagged
+ */
+bool __fscache_maybe_release_page(struct fscache_cookie *cookie,
+				  struct page *page,
+				  gfp_t gfp)
+{
+	struct page *xpage;
+	void *val;
+
+	_enter("%p,%p,%x", cookie, page, gfp);
+
+	rcu_read_lock();
+	val = radix_tree_lookup(&cookie->stores, page->index);
+	if (!val) {
+		rcu_read_unlock();
+		fscache_stat(&fscache_n_store_vmscan_not_storing);
+		__fscache_uncache_page(cookie, page);
+		return true;
+	}
+
+	/* see if the page is actually undergoing storage - if so we can't get
+	 * rid of it till the cache has finished with it */
+	if (radix_tree_tag_get(&cookie->stores, page->index,
+			       FSCACHE_COOKIE_STORING_TAG)) {
+		rcu_read_unlock();
+		goto page_busy;
+	}
+
+	/* the page is pending storage, so we attempt to cancel the store and
+	 * discard the store request so that the page can be reclaimed */
+	spin_lock(&cookie->stores_lock);
+	rcu_read_unlock();
+
+	if (radix_tree_tag_get(&cookie->stores, page->index,
+			       FSCACHE_COOKIE_STORING_TAG)) {
+		/* the page started to undergo storage whilst we were looking,
+		 * so now we can only wait or return */
+		spin_unlock(&cookie->stores_lock);
+		goto page_busy;
+	}
+
+	xpage = radix_tree_delete(&cookie->stores, page->index);
+	spin_unlock(&cookie->stores_lock);
+
+	if (xpage) {
+		fscache_stat(&fscache_n_store_vmscan_cancelled);
+		fscache_stat(&fscache_n_store_radix_deletes);
+		ASSERTCMP(xpage, ==, page);
+	} else {
+		fscache_stat(&fscache_n_store_vmscan_gone);
+	}
+
+	wake_up_bit(&cookie->flags, 0);
+	if (xpage)
+		page_cache_release(xpage);
+	__fscache_uncache_page(cookie, page);
+	return true;
+
+page_busy:
+	/* we might want to wait here, but that could deadlock the allocator as
+	 * the slow-work threads writing to the cache may all end up sleeping
+	 * on memory allocation */
+	fscache_stat(&fscache_n_store_vmscan_busy);
+	return false;
+}
+EXPORT_SYMBOL(__fscache_maybe_release_page);
+
+/*
  * note that a page has finished being written to the cache
  */
 static void fscache_end_page_write(struct fscache_object *object,
@@ -57,6 +126,8 @@ static void fscache_end_page_write(struct fscache_object *object,
 		/* delete the page from the tree if it is now no longer
 		 * pending */
 		spin_lock(&cookie->stores_lock);
+		radix_tree_tag_clear(&cookie->stores, page->index,
+				     FSCACHE_COOKIE_STORING_TAG);
 		if (!radix_tree_tag_get(&cookie->stores, page->index,
 					FSCACHE_COOKIE_PENDING_TAG)) {
 			fscache_stat(&fscache_n_store_radix_deletes);
@@ -640,8 +711,12 @@ static void fscache_write_op(struct fscache_operation *_op)
 		goto superseded;
 	}
 
-	radix_tree_tag_clear(&cookie->stores, page->index,
-			     FSCACHE_COOKIE_PENDING_TAG);
+	if (page) {
+		radix_tree_tag_set(&cookie->stores, page->index,
+				   FSCACHE_COOKIE_STORING_TAG);
+		radix_tree_tag_clear(&cookie->stores, page->index,
+				     FSCACHE_COOKIE_PENDING_TAG);
+	}
 
 	spin_unlock(&cookie->stores_lock);
 	spin_unlock(&object->lock);
diff --git a/fs/fscache/stats.c b/fs/fscache/stats.c
index 045ba396dbf..cda69994e06 100644
--- a/fs/fscache/stats.c
+++ b/fs/fscache/stats.c
@@ -63,6 +63,11 @@ atomic_t fscache_n_store_pages;
 atomic_t fscache_n_store_radix_deletes;
 atomic_t fscache_n_store_pages_over_limit;
 
+atomic_t fscache_n_store_vmscan_not_storing;
+atomic_t fscache_n_store_vmscan_gone;
+atomic_t fscache_n_store_vmscan_busy;
+atomic_t fscache_n_store_vmscan_cancelled;
+
 atomic_t fscache_n_marks;
 atomic_t fscache_n_uncaches;
 
@@ -211,6 +216,12 @@ static int fscache_stats_show(struct seq_file *m, void *v)
 		   atomic_read(&fscache_n_store_radix_deletes),
 		   atomic_read(&fscache_n_store_pages_over_limit));
 
+	seq_printf(m, "VmScan : nos=%u gon=%u bsy=%u can=%u\n",
+		   atomic_read(&fscache_n_store_vmscan_not_storing),
+		   atomic_read(&fscache_n_store_vmscan_gone),
+		   atomic_read(&fscache_n_store_vmscan_busy),
+		   atomic_read(&fscache_n_store_vmscan_cancelled));
+
 	seq_printf(m, "Ops    : pend=%u run=%u enq=%u can=%u rej=%u\n",
 		   atomic_read(&fscache_n_op_pend),
 		   atomic_read(&fscache_n_op_run),
diff --git a/fs/nfs/fscache.c b/fs/nfs/fscache.c
index 70fad69eb95..fa588006588 100644
--- a/fs/nfs/fscache.c
+++ b/fs/nfs/fscache.c
@@ -359,17 +359,13 @@ int nfs_fscache_release_page(struct page *page, gfp_t gfp)
 
 	BUG_ON(!cookie);
 
-	if (fscache_check_page_write(cookie, page)) {
-		if (!(gfp & __GFP_WAIT))
-			return 0;
-		fscache_wait_on_page_write(cookie, page);
-	}
-
 	if (PageFsCache(page)) {
 		dfprintk(FSCACHE, "NFS: fscache releasepage (0x%p/0x%p/0x%p)\n",
 			 cookie, page, nfsi);
 
-		fscache_uncache_page(cookie, page);
+		if (!fscache_maybe_release_page(cookie, page, gfp))
+			return 0;
+
 		nfs_add_fscache_stats(page->mapping->host,
 				      NFSIOS_FSCACHE_PAGES_UNCACHED, 1);
 	}