affs: get rid of affs_sync_super

This patch makes affs stop using the VFS '->write_super()' method along with
the 's_dirt' superblock flag, because they are on their way out.

The whole "superblock write-out" VFS infrastructure is served by the
'sync_supers()' kernel thread, which wakes up every 5 (by default) seconds and
writes out all dirty superblocks using the '->write_super()' call-back.  But the
problem with this thread is that it wastes power by waking up the system every
5 seconds, even if there are no diry superblocks, or there are no client
file-systems which would need this (e.g., btrfs does not use
'->write_super()'). So we want to kill it completely and thus, we need to make
file-systems to stop using the '->write_super()' VFS service, and then remove
it together with the kernel thread.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 45 insertions, 13 deletions

diff --git a/fs/affs/affs.h b/fs/affs/affs.h
index 5a726e992245..3a130e27eb15 100644
--- a/fs/affs/affs.h
+++ b/fs/affs/affs.h
@@ -3,6 +3,7 @@
 #include <linux/buffer_head.h>
 #include <linux/amigaffs.h>
 #include <linux/mutex.h>
+#include <linux/workqueue.h>
 
 /* AmigaOS allows file names with up to 30 characters length.
  * Names longer than that will be silently truncated. If you
@@ -101,6 +102,9 @@ struct affs_sb_info {
         char s_volume[32];              /* Volume prefix for absolute symlinks. */
         spinlock_t symlink_lock;        /* protects the previous two */
         struct super_block *sb;         /* the VFS superblock object */
+        int work_queued;                /* non-zero delayed work is queued */
+        struct delayed_work sb_work;    /* superblock flush delayed work */
+        spinlock_t work_lock;           /* protects sb_work and work_queued */
 };
 
 #define SF_INTL         0x0001          /* International filesystem. */
@@ -121,6 +125,8 @@ static inline struct affs_sb_info *AFFS_SB(struct super_block *sb)
         return sb->s_fs_info;
 }
 
+void affs_mark_sb_dirty(struct super_block *sb);
+
 /* amigaffs.c */
 
 extern int      affs_insert_hash(struct inode *inode, struct buffer_head *bh);
diff --git a/fs/affs/bitmap.c b/fs/affs/bitmap.c
index 3e262711ae06..6e0be43ef6ef 100644
--- a/fs/affs/bitmap.c
+++ b/fs/affs/bitmap.c
@@ -103,7 +103,7 @@ affs_free_block(struct super_block *sb, u32 block)
         *(__be32 *)bh->b_data = cpu_to_be32(tmp - mask);
 
         mark_buffer_dirty(bh);
-        sb->s_dirt = 1;
+        affs_mark_sb_dirty(sb);
         bm->bm_free++;
 
         mutex_unlock(&sbi->s_bmlock);
@@ -248,7 +248,7 @@ find_bit:
         *(__be32 *)bh->b_data = cpu_to_be32(tmp + mask);
 
         mark_buffer_dirty(bh);
-        sb->s_dirt = 1;
+        affs_mark_sb_dirty(sb);
 
         mutex_unlock(&sbi->s_bmlock);
 
diff --git a/fs/affs/super.c b/fs/affs/super.c
index 0496cbbeda1b..c70f1e5fc024 100644
--- a/fs/affs/super.c
+++ b/fs/affs/super.c
@@ -17,6 +17,7 @@
 #include <linux/magic.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
+#include <linux/writeback.h>
 #include "affs.h"
 
 extern struct timezone sys_tz;
@@ -47,6 +48,7 @@ affs_put_super(struct super_block *sb)
         struct affs_sb_info *sbi = AFFS_SB(sb);
         pr_debug("AFFS: put_super()\n");
 
+        cancel_delayed_work_sync(&sbi->sb_work);
         kfree(sbi->s_prefix);
         affs_free_bitmap(sb);
         affs_brelse(sbi->s_root_bh);
@@ -54,23 +56,45 @@ affs_put_super(struct super_block *sb)
         sb->s_fs_info = NULL;
 }
 
-static void
-affs_write_super(struct super_block *sb)
-{
-        if (!(sb->s_flags & MS_RDONLY))
-                affs_commit_super(sb, 1);
-        sb->s_dirt = 0;
-        pr_debug("AFFS: write_super() at %lu, clean=2\n", get_seconds());
-}
-
 static int
 affs_sync_fs(struct super_block *sb, int wait)
 {
         affs_commit_super(sb, wait);
-        sb->s_dirt = 0;
         return 0;
 }
 
+static void flush_superblock(struct work_struct *work)
+{
+        struct affs_sb_info *sbi;
+        struct super_block *sb;
+
+        sbi = container_of(work, struct affs_sb_info, sb_work.work);
+        sb = sbi->sb;
+
+        spin_lock(&sbi->work_lock);
+        sbi->work_queued = 0;
+        spin_unlock(&sbi->work_lock);
+
+        affs_commit_super(sb, 1);
+}
+
+void affs_mark_sb_dirty(struct super_block *sb)
+{
+        struct affs_sb_info *sbi = AFFS_SB(sb);
+        unsigned long delay;
+
+        if (sb->s_flags & MS_RDONLY)
+               return;
+
+        spin_lock(&sbi->work_lock);
+        if (!sbi->work_queued) {
+               delay = msecs_to_jiffies(dirty_writeback_interval * 10);
+               queue_delayed_work(system_long_wq, &sbi->sb_work, delay);
+               sbi->work_queued = 1;
+        }
+        spin_unlock(&sbi->work_lock);
+}
+
 static struct kmem_cache * affs_inode_cachep;
 
 static struct inode *affs_alloc_inode(struct super_block *sb)
@@ -132,7 +156,6 @@ static const struct super_operations affs_sops = {
         .write_inode    = affs_write_inode,
         .evict_inode    = affs_evict_inode,
         .put_super      = affs_put_super,
-        .write_super    = affs_write_super,
         .sync_fs        = affs_sync_fs,
         .statfs         = affs_statfs,
         .remount_fs     = affs_remount,
@@ -302,6 +325,8 @@ static int affs_fill_super(struct super_block *sb, void *data, int silent)
         sbi->sb = sb;
         mutex_init(&sbi->s_bmlock);
         spin_lock_init(&sbi->symlink_lock);
+        spin_lock_init(&sbi->work_lock);
+        INIT_DELAYED_WORK(&sbi->sb_work, flush_superblock);
 
         if (!parse_options(data,&uid,&gid,&i,&reserved,&root_block,
                                 &blocksize,&sbi->s_prefix,
@@ -526,6 +551,7 @@ affs_remount(struct super_block *sb, int *flags, char *data)
                 return -EINVAL;
         }
 
+        flush_delayed_work_sync(&sbi->sb_work);
         replace_mount_options(sb, new_opts);
 
         sbi->s_flags = mount_flags;