fscache, cachefiles: Display stats of no-space events

Add stat counters of no-space events that caused caching not to happen and
display in /proc/fs/fscache/stats.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819653216.215744.17210522251617386509.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906958369.143852.7257100711818401748.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967166917.1823006.14842444049198947892.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021566184.640689.4417328329632709265.stgit@warthog.procyon.org.uk/ # v4

fs/cachefiles/cache.c

@@ -147,7 +147,7 @@ int cachefiles_add_cache(struct cachefiles_cache *cache)
 	pr_info("File cache on %s registered\n", cache_cookie->name);
 
 	/* check how much space the cache has */
-	cachefiles_has_space(cache, 0, 0);
+	cachefiles_has_space(cache, 0, 0, cachefiles_has_space_check);
 	cachefiles_end_secure(cache, saved_cred);
 	_leave(" = 0 [%px]", cache->cache);
 	return 0;
@@ -175,7 +175,8 @@ int cachefiles_add_cache(struct cachefiles_cache *cache)
  * cache
  */
 int cachefiles_has_space(struct cachefiles_cache *cache,
-			 unsigned fnr, unsigned bnr)
+			 unsigned fnr, unsigned bnr,
+			 enum cachefiles_has_space_for reason)
 {
 	struct kstatfs stats;
 	u64 b_avail, b_writing;
@@ -233,7 +234,7 @@ int cachefiles_has_space(struct cachefiles_cache *cache,
 	ret = -ENOBUFS;
 	if (stats.f_ffree < cache->fstop ||
 	    b_avail < cache->bstop)
-		goto begin_cull;
+		goto stop_and_begin_cull;
 
 	ret = 0;
 	if (stats.f_ffree < cache->fcull ||
@@ -252,6 +253,17 @@ int cachefiles_has_space(struct cachefiles_cache *cache,
 	//_leave(" = 0");
 	return 0;
 
+stop_and_begin_cull:
+	switch (reason) {
+	case cachefiles_has_space_for_write:
+		fscache_count_no_write_space();
+		break;
+	case cachefiles_has_space_for_create:
+		fscache_count_no_create_space();
+		break;
+	default:
+		break;
+	}
 begin_cull:
 	if (!test_and_set_bit(CACHEFILES_CULLING, &cache->flags)) {
 		_debug("### CULL CACHE ###");

fs/cachefiles/daemon.c

@@ -170,7 +170,7 @@ static ssize_t cachefiles_daemon_read(struct file *file, char __user *_buffer,
 		return 0;
 
 	/* check how much space the cache has */
-	cachefiles_has_space(cache, 0, 0);
+	cachefiles_has_space(cache, 0, 0, cachefiles_has_space_check);
 
 	/* summarise */
 	f_released = atomic_xchg(&cache->f_released, 0);

fs/cachefiles/internal.h

@@ -130,10 +130,17 @@ static inline void cachefiles_state_changed(struct cachefiles_cache *cache)
  * cache.c
  */
 extern int cachefiles_add_cache(struct cachefiles_cache *cache);
-extern int cachefiles_has_space(struct cachefiles_cache *cache,
-				unsigned fnr, unsigned bnr);
 extern void cachefiles_withdraw_cache(struct cachefiles_cache *cache);
 
+enum cachefiles_has_space_for {
+	cachefiles_has_space_check,
+	cachefiles_has_space_for_write,
+	cachefiles_has_space_for_create,
+};
+extern int cachefiles_has_space(struct cachefiles_cache *cache,
+				unsigned fnr, unsigned bnr,
+				enum cachefiles_has_space_for reason);
+
 /*
  * daemon.c
  */

fs/cachefiles/io.c

@@ -468,7 +468,8 @@ static int __cachefiles_prepare_write(struct netfs_cache_resources *cres,
 	 * space, we need to see if it's fully allocated.  If it's not, we may
 	 * want to cull it.
 	 */
-	if (cachefiles_has_space(cache, 0, *_len / PAGE_SIZE) == 0)
+	if (cachefiles_has_space(cache, 0, *_len / PAGE_SIZE,
+				 cachefiles_has_space_check) == 0)
 		return 0; /* Enough space to simply overwrite the whole block */
 
 	pos = cachefiles_inject_read_error();
@@ -483,6 +484,7 @@ static int __cachefiles_prepare_write(struct netfs_cache_resources *cres,
 		return 0; /* Fully allocated */
 
 	/* Partially allocated, but insufficient space: cull. */
+	fscache_count_no_write_space();
 	ret = cachefiles_inject_remove_error();
 	if (ret == 0)
 		ret = vfs_fallocate(file, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
@@ -498,7 +500,8 @@ static int __cachefiles_prepare_write(struct netfs_cache_resources *cres,
 	return ret;
 
 check_space:
-	return cachefiles_has_space(cache, 0, *_len / PAGE_SIZE);
+	return cachefiles_has_space(cache, 0, *_len / PAGE_SIZE,
+				    cachefiles_has_space_for_write);
 }
 
 static int cachefiles_prepare_write(struct netfs_cache_resources *cres,

fs/cachefiles/namei.c

@@ -115,7 +115,8 @@ struct dentry *cachefiles_get_directory(struct cachefiles_cache *cache,
 
 	/* we need to create the subdir if it doesn't exist yet */
 	if (d_is_negative(subdir)) {
-		ret = cachefiles_has_space(cache, 1, 0);
+		ret = cachefiles_has_space(cache, 1, 0,
+					   cachefiles_has_space_for_create);
 		if (ret < 0)
 			goto mkdir_error;
 
@@ -513,7 +514,8 @@ static bool cachefiles_create_file(struct cachefiles_object *object)
 	struct file *file;
 	int ret;
 
-	ret = cachefiles_has_space(object->volume->cache, 1, 0);
+	ret = cachefiles_has_space(object->volume->cache, 1, 0,
+				   cachefiles_has_space_for_create);
 	if (ret < 0)
 		return false;
 

fs/fscache/stats.c

@@ -42,6 +42,10 @@ atomic_t fscache_n_read;
 EXPORT_SYMBOL(fscache_n_read);
 atomic_t fscache_n_write;
 EXPORT_SYMBOL(fscache_n_write);
+atomic_t fscache_n_no_write_space;
+EXPORT_SYMBOL(fscache_n_no_write_space);
+atomic_t fscache_n_no_create_space;
+EXPORT_SYMBOL(fscache_n_no_create_space);
 
 /*
  * display the general statistics
@@ -82,6 +86,10 @@ int fscache_stats_show(struct seq_file *m, void *v)
 		   atomic_read(&fscache_n_relinquishes_retire),
 		   atomic_read(&fscache_n_relinquishes_dropped));
 
+	seq_printf(m, "NoSpace: nwr=%u ncr=%u\n",
+		   atomic_read(&fscache_n_no_write_space),
+		   atomic_read(&fscache_n_no_create_space));
+
 	seq_printf(m, "IO     : rd=%u wr=%u\n",
 		   atomic_read(&fscache_n_read),
 		   atomic_read(&fscache_n_write));

include/linux/fscache-cache.h

@@ -186,11 +186,17 @@ static inline void fscache_wait_for_objects(struct fscache_cache *cache)
 #ifdef CONFIG_FSCACHE_STATS
 extern atomic_t fscache_n_read;
 extern atomic_t fscache_n_write;
+extern atomic_t fscache_n_no_write_space;
+extern atomic_t fscache_n_no_create_space;
 #define fscache_count_read() atomic_inc(&fscache_n_read)
 #define fscache_count_write() atomic_inc(&fscache_n_write)
+#define fscache_count_no_write_space() atomic_inc(&fscache_n_no_write_space)
+#define fscache_count_no_create_space() atomic_inc(&fscache_n_no_create_space)
 #else
 #define fscache_count_read() do {} while(0)
 #define fscache_count_write() do {} while(0)
+#define fscache_count_no_write_space() do {} while(0)
+#define fscache_count_no_create_space() do {} while(0)
 #endif
 
 #endif /* _LINUX_FSCACHE_CACHE_H */