[PATCH 09/16] cifs: register a shrinker to manage cached_dirents

[Steve French <smfrench@gmail.com>]

From: Shyam Prasad N <sprasad@microsoft.com>

Since the cached_dirents are now backed by folioq, we do not need
a timed cleanup of these cfids anymore. This change registers a
shrinker with the mm layer for the dircache. If mm needs to free up
memory or flush the cache, it can inform cifs about this using the
shrinker interface.

Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
---
 fs/smb/client/cifs_debug.c |  18 +------
 fs/smb/client/cifsfs.c     | 104 ++++++++++++++++++++++++++++++++++++-
 fs/smb/client/cifsfs.h     |   4 ++
 3 files changed, 108 insertions(+), 18 deletions(-)

diff --git a/fs/smb/client/cifs_debug.c b/fs/smb/client/cifs_debug.c
index b35863eb2a66..131af7333fc5 100644
--- a/fs/smb/client/cifs_debug.c
+++ b/fs/smb/client/cifs_debug.c
@@ -375,22 +375,8 @@ static ssize_t cifs_debug_dirs_proc_write(struct file *file, const char __user *
 	if (rc)
 		return rc;
 
-	if (v == 0) {
-		struct TCP_Server_Info *server;
-		struct cifs_ses *ses;
-		struct cifs_tcon *tcon;
-
-		spin_lock(&cifs_tcp_ses_lock);
-		list_for_each_entry(server, &cifs_tcp_ses_list, tcp_ses_list) {
-			list_for_each_entry(ses, &server->smb_ses_list, smb_ses_list) {
-				if (cifs_ses_exiting(ses))
-					continue;
-				list_for_each_entry(tcon, &ses->tcon_list, tcon_list)
-					invalidate_all_cached_dirs(tcon, false);
-			}
-		}
-		spin_unlock(&cifs_tcp_ses_lock);
-	}
+	if (v == 0)
+		cifs_shrink_dir_caches(false, ULONG_MAX);
 
 	return count;
 }
diff --git a/fs/smb/client/cifsfs.c b/fs/smb/client/cifsfs.c
index 834859fbd527..fd725ee4293b 100644
--- a/fs/smb/client/cifsfs.c
+++ b/fs/smb/client/cifsfs.c
@@ -30,6 +30,7 @@
 #include <linux/uuid.h>
 #include <linux/xattr.h>
 #include <linux/mm.h>
+#include <linux/shrinker.h>
 #include <linux/key-type.h>
 #include <linux/fileattr.h>
 #include <uapi/linux/magic.h>
@@ -125,10 +126,95 @@ MODULE_PARM_DESC(dir_cache_timeout, "Number of seconds to cache directory conten
 				 "Range: 1 to 65000 seconds, 0 to disable caching dir contents");
 /* Module-wide total cached dirents (in bytes) across all tcons */
 atomic64_t cifs_dircache_bytes_used = ATOMIC64_INIT(0);
+static struct shrinker *cifs_dircache_shrinker;
 
 atomic_t cifs_sillycounter;
 atomic_t cifs_tmpcounter;
 
+/**
+ * cifs_shrink_dir_caches - shrink dir caches by a specific size
+ * @wait: wait for server responses to close
+ * @nr_to_free: number of pages to shrink the dir cache by (pass ULONG_MAX to
+ * free everything)
+ *
+ * Shrinks dir caches by a specific target size.
+ */
+unsigned long cifs_shrink_dir_caches(bool wait, unsigned long nr_to_free)
+{
+	struct TCP_Server_Info *server;
+	struct cifs_ses *ses;
+	struct cifs_tcon *tcon;
+	u64 before, after, freed_bytes = 0;
+	u64 target_bytes;
+
+	before = atomic64_read(&cifs_dircache_bytes_used);
+	if (nr_to_free == ULONG_MAX)
+		target_bytes = U64_MAX;
+	else
+		target_bytes = (u64)nr_to_free * PAGE_SIZE;
+
+	spin_lock(&cifs_tcp_ses_lock);
+	list_for_each_entry(server, &cifs_tcp_ses_list, tcp_ses_list) {
+		list_for_each_entry(ses, &server->smb_ses_list, smb_ses_list) {
+			if (cifs_ses_exiting(ses))
+				continue;
+			list_for_each_entry(tcon, &ses->tcon_list, tcon_list) {
+				invalidate_all_cached_dirs(tcon, false);
+				after = atomic64_read(&cifs_dircache_bytes_used);
+				if (after < before)
+					freed_bytes = before - after;
+				if (freed_bytes >= target_bytes)
+					goto out_unlock;
+			}
+		}
+	}
+out_unlock:
+	spin_unlock(&cifs_tcp_ses_lock);
+
+	if (wait)
+		flush_workqueue(cfid_put_wq);
+
+	after = atomic64_read(&cifs_dircache_bytes_used);
+	if (after >= before)
+		return 0;
+	return (unsigned long)(before - after);
+}
+
+static unsigned long cifs_dircache_shrinker_count(struct shrinker *shrink,
+						   struct shrink_control *sc)
+{
+	u64 bytes = atomic64_read(&cifs_dircache_bytes_used);
+
+	(void)shrink;
+	(void)sc;
+
+	return DIV_ROUND_UP_ULL(bytes, PAGE_SIZE);
+}
+
+static unsigned long cifs_dircache_shrinker_scan(struct shrinker *shrink,
+						  struct shrink_control *sc)
+{
+	unsigned long freed_bytes;
+
+	(void)shrink;
+
+	if (!sc->nr_to_scan)
+		return 0;
+
+	if (!atomic64_read(&cifs_dircache_bytes_used))
+		return SHRINK_STOP;
+
+	/*
+	 * Shrinker scan can run from reclaim context, so avoid synchronously
+	 * flushing worker queues here to prevent long stalls/deadlocks.
+	 */
+	freed_bytes = cifs_shrink_dir_caches(false, max_t(unsigned long, 1, sc->nr_to_scan));
+	if (!freed_bytes)
+		return SHRINK_STOP;
+
+	return DIV_ROUND_UP_ULL(freed_bytes, PAGE_SIZE);
+}
+
 #ifdef CONFIG_CIFS_STATS2
 unsigned int slow_rsp_threshold = 1;
 module_param(slow_rsp_threshold, uint, 0644);
@@ -2087,10 +2173,19 @@ init_cifs(void)
 	if (rc)
 		goto out_destroy_mids;
 
+	cifs_dircache_shrinker = shrinker_alloc(0, "cifs-dircache");
+	if (!cifs_dircache_shrinker) {
+		rc = -ENOMEM;
+		goto out_destroy_request_bufs;
+	}
+	cifs_dircache_shrinker->count_objects = cifs_dircache_shrinker_count;
+	cifs_dircache_shrinker->scan_objects = cifs_dircache_shrinker_scan;
+	shrinker_register(cifs_dircache_shrinker);
+
 #ifdef CONFIG_CIFS_DFS_UPCALL
 	rc = dfs_cache_init();
 	if (rc)
-		goto out_destroy_request_bufs;
+		goto out_free_dircache_shrinker;
 #endif /* CONFIG_CIFS_DFS_UPCALL */
 #ifdef CONFIG_CIFS_UPCALL
 	rc = init_cifs_spnego();
@@ -2132,8 +2227,11 @@ init_cifs(void)
 #endif
 #ifdef CONFIG_CIFS_DFS_UPCALL
 	dfs_cache_destroy();
-out_destroy_request_bufs:
+out_free_dircache_shrinker:
 #endif
+	shrinker_free(cifs_dircache_shrinker);
+	cifs_dircache_shrinker = NULL;
+out_destroy_request_bufs:
 	cifs_destroy_request_bufs();
 out_destroy_mids:
 	destroy_mids();
@@ -2166,6 +2264,8 @@ exit_cifs(void)
 	cifs_dbg(NOISY, "exit_smb3\n");
 	unregister_filesystem(&cifs_fs_type);
 	unregister_filesystem(&smb3_fs_type);
+	shrinker_free(cifs_dircache_shrinker);
+	cifs_dircache_shrinker = NULL;
 	cifs_release_automount_timer();
 	exit_cifs_idmap();
 #ifdef CONFIG_CIFS_SWN_UPCALL
diff --git a/fs/smb/client/cifsfs.h b/fs/smb/client/cifsfs.h
index 008b1d373245..a5bf711e4de7 100644
--- a/fs/smb/client/cifsfs.h
+++ b/fs/smb/client/cifsfs.h
@@ -125,6 +125,10 @@ extern const struct dentry_operations cifs_ci_dentry_ops;
 
 struct vfsmount *cifs_d_automount(struct path *path);
 
+/* Functions related to dir cache */
+unsigned long cifs_shrink_dir_caches(bool wait,
+				     unsigned long nr_to_free);
+
 /* Functions related to symlinks */
 const char *cifs_get_link(struct dentry *dentry, struct inode *inode,
 			  struct delayed_call *done);
-- 
2.53.0