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SubjectRe: [PATCH] vfs: Merge sync_supers(), sync_filesystems() and sync_blockdevs()
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On Wed, 2009-04-22 at 17:56 +0200, Jan Kara wrote:
> These three functions are quite similar so merge them to save superblock list
> traversal code. As a bonus we get livelock avoidance for all these superblock
> traversals. Also remove the condition that if wait == 0 and sb->s_dirt is
> not set, then ->sync_fs() is not called. This does not really make much sence
> since s_dirt is generally used by filesystem to mean that ->write_super() needs
> to be called. But ->sync_fs() does different things. I even suspect that some
> filesystems (btrfs?) sets s_dirt just to fool this logic.
>
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
> fs/super.c | 104 ++++++++++++++------------------------------------
> fs/sync.c | 12 ++++--
> include/linux/fs.h | 11 +++--
> mm/page-writeback.c | 2 +-
> 4 files changed, 44 insertions(+), 85 deletions(-)
>
> diff --git a/fs/super.c b/fs/super.c
> index 4f56333..6d6209e 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -413,58 +413,24 @@ void drop_super(struct super_block *sb)
>
> EXPORT_SYMBOL(drop_super);
>
> -static inline void write_super(struct super_block *sb)
> -{
> - lock_super(sb);
> - if (sb->s_root && sb->s_dirt)
> - if (sb->s_op->write_super)
> - sb->s_op->write_super(sb);
> - unlock_super(sb);
> -}
> -
> -/*
> - * Note: check the dirty flag before waiting, so we don't
> - * hold up the sync while mounting a device. (The newly
> - * mounted device won't need syncing.)
> - */
> -void sync_supers(void)
> -{
> - struct super_block *sb;
> -
> - spin_lock(&sb_lock);
> -restart:
> - list_for_each_entry(sb, &super_blocks, s_list) {
> - if (sb->s_dirt) {
> - sb->s_count++;
> - spin_unlock(&sb_lock);
> - down_read(&sb->s_umount);
> - write_super(sb);
> - up_read(&sb->s_umount);
> - spin_lock(&sb_lock);
> - if (__put_super_and_need_restart(sb))
> - goto restart;
> - }
> - }
> - spin_unlock(&sb_lock);
> -}
> -
> /*
> - * Call the ->sync_fs super_op against all filesystems which are r/w and
> - * which implement it.
> + * Call the ->write_super, ->sync_fs, sync_blockdev() against all filesystems
> + * which are r/w and which implement it.
> *
> - * This operation is careful to avoid the livelock which could easily happen
> - * if two or more filesystems are being continuously dirtied. s_need_sync_fs
> - * is used only here. We set it against all filesystems and then clear it as
> - * we sync them. So redirtied filesystems are skipped.
> + * This operation is careful to avoid the livelock. Currently it's not so easy
> + * to trigger as it used to be - we restart scanning the superblock list only
> + * if the superblock got unmounted under us - but it's better to be safe and it
> + * doesn't cost us much. s_need_sync is used only here. We set it against all
> + * filesystems and then clear it as we sync them. So redirtied filesystems are
> + * skipped.
> *
> * But if process A is currently running sync_filesystems and then process B
> - * calls sync_filesystems as well, process B will set all the s_need_sync_fs
> - * flags again, which will cause process A to resync everything. Fix that with
> - * a local mutex.
> + * calls sync_filesystems as well, process B will set all the s_need_sync flags
> + * again, which will cause process A to resync everything. Fix that with a
> + * local mutex.
> *
> - * (Fabian) Avoid sync_fs with clean fs & wait mode 0
> */
> -void sync_filesystems(int wait)
> +void sync_filesystems(int what, int wait)
> {
> struct super_block *sb;
> static DEFINE_MUTEX(mutex);
> @@ -472,26 +438,37 @@ void sync_filesystems(int wait)
> mutex_lock(&mutex); /* Could be down_interruptible */
> spin_lock(&sb_lock);
> list_for_each_entry(sb, &super_blocks, s_list) {
> - if (!sb->s_op->sync_fs)
> + if ((!sb->s_op->sync_fs || !(what & FSSYNC_FS)) &&
> + (!sb->s_op->write_super || !(what & FSSYNC_SUPER)) &&
> + !(what & FSSYNC_BDEV))

Ditto. There should be a check for sb->s_bdev here too...

> continue;
> if (sb->s_flags & MS_RDONLY)
> continue;
> - sb->s_need_sync_fs = 1;
> + sb->s_need_sync = 1;
> }
>
> restart:
> list_for_each_entry(sb, &super_blocks, s_list) {
> - if (!sb->s_need_sync_fs)
> + if (!sb->s_need_sync)
> continue;
> - sb->s_need_sync_fs = 0;
> + sb->s_need_sync = 0;
> if (sb->s_flags & MS_RDONLY)
> continue; /* hm. Was remounted r/o meanwhile */
> sb->s_count++;
> spin_unlock(&sb_lock);
> down_read(&sb->s_umount);
> async_synchronize_full_domain(&sb->s_async_list);
> - if (sb->s_root && (wait || sb->s_dirt))
> - sb->s_op->sync_fs(sb, wait);
> + if (sb->s_root) {
> + lock_super(sb);
> + if (what & FSSYNC_SUPER && sb->s_dirt &&
> + sb->s_op->write_super)
> + sb->s_op->write_super(sb);
> + unlock_super(sb);
> + if (what & FSSYNC_FS && sb->s_op->sync_fs)
> + sb->s_op->sync_fs(sb, wait);
> + if (what & FSSYNC_BDEV)
> + sync_blockdev(sb->s_bdev);
> + }
> up_read(&sb->s_umount);
> /* restart only when sb is no longer on the list */
> spin_lock(&sb_lock);
> @@ -502,29 +479,6 @@ restart:
> mutex_unlock(&mutex);
> }
>
> -/*
> - * Sync all block devices underlying some superblock
> - */
> -void sync_blockdevs(void)
> -{
> - struct super_block *sb;
> -
> - spin_lock(&sb_lock);
> -restart:
> - list_for_each_entry(sb, &super_blocks, s_list) {
> - sb->s_count++;
> - spin_unlock(&sb_lock);
> - down_read(&sb->s_umount);
> - if (sb->s_root)
> - sync_blockdev(sb->s_bdev);
> - up_read(&sb->s_umount);
> - spin_lock(&sb_lock);
> - if (__put_super_and_need_restart(sb))
> - goto restart;
> - }
> - spin_unlock(&sb_lock);
> -}
> -
> /**
> * get_super - get the superblock of a device
> * @bdev: device to get the superblock for
> diff --git a/fs/sync.c b/fs/sync.c
> index fa14e42..3c677ee 100644
> --- a/fs/sync.c
> +++ b/fs/sync.c
> @@ -26,11 +26,15 @@ static void do_sync(unsigned long wait)
> wakeup_pdflush(0);
> sync_inodes(0); /* All mappings, inodes and their blockdevs */
> vfs_dq_sync(NULL);
> + sync_filesystems(FSSYNC_FS, 0); /* Start syncing the filesystems */
> + /*
> + * We have to reliably submit IO for all the inodes before writing
> + * super blocks and calling sync_fs(). Otherwise superblock could miss
> + * some updates or journal could still have uncommitted data.
> + */
> sync_inodes(wait); /* Mappings, inodes and blockdevs, again. */
> - sync_supers(); /* Write the superblocks */
> - sync_filesystems(0); /* Start syncing the filesystems */
> - sync_filesystems(wait); /* Waitingly sync the filesystems */
> - sync_blockdevs();
> + /* Waitingly sync the filesystems */
> + sync_filesystems(FSSYNC_SUPER | FSSYNC_FS | FSSYNC_BDEV, wait);
> if (!wait)
> printk("Emergency Sync complete\n");
> if (unlikely(laptop_mode))
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 4bad02e..2758e75 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1321,7 +1321,7 @@ struct super_block {
> struct rw_semaphore s_umount;
> struct mutex s_lock;
> int s_count;
> - int s_need_sync_fs;
> + int s_need_sync;
> atomic_t s_active;
> #ifdef CONFIG_SECURITY
> void *s_security;
> @@ -1942,7 +1942,6 @@ extern void bdput(struct block_device *);
> extern struct block_device *open_by_devnum(dev_t, fmode_t);
> extern void invalidate_bdev(struct block_device *);
> extern int sync_blockdev(struct block_device *bdev);
> -extern void sync_blockdevs(void);
> extern struct super_block *freeze_bdev(struct block_device *);
> extern void emergency_thaw_all(void);
> extern int thaw_bdev(struct block_device *bdev, struct super_block *sb);
> @@ -1952,7 +1951,6 @@ extern int fsync_no_super(struct block_device *);
> #else
> static inline void bd_forget(struct inode *inode) {}
> static inline int sync_blockdev(struct block_device *bdev) { return 0; }
> -static inline void sync_blockdevs(void) { }
> static inline void invalidate_bdev(struct block_device *bdev) {}
>
> static inline struct super_block *freeze_bdev(struct block_device *sb)
> @@ -2082,8 +2080,11 @@ extern int filemap_fdatawrite_range(struct address_space *mapping,
> loff_t start, loff_t end);
>
> extern int vfs_fsync(struct file *file, struct dentry *dentry, int datasync);
> -extern void sync_supers(void);
> -extern void sync_filesystems(int wait);
> +/* Flags telling what should be synced by sync_filesystems() */
> +#define FSSYNC_FS 1
> +#define FSSYNC_SUPER 2
> +#define FSSYNC_BDEV 4
> +extern void sync_filesystems(int what, int wait);
> extern void __fsync_super(struct super_block *sb);
> extern void emergency_sync(void);
> extern void emergency_remount(void);
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 30351f0..05a2948 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -768,7 +768,7 @@ static void wb_kupdate(unsigned long arg)
> .range_cyclic = 1,
> };
>
> - sync_supers();
> + sync_filesystems(FSSYNC_SUPER, 0);
>
> oldest_jif = jiffies - msecs_to_jiffies(dirty_expire_interval);
> start_jif = jiffies;



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