Commit e913fc82 authored by Jens Axboe's avatar Jens Axboe
Browse files

writeback: fix WB_SYNC_NONE writeback from umount 



When umount calls sync_filesystem(), we first do a WB_SYNC_NONE
writeback to kick off writeback of pending dirty inodes, then follow
that up with a WB_SYNC_ALL to wait for it. Since umount already holds
the sb s_umount mutex, WB_SYNC_NONE ends up doing nothing and all
writeback happens as WB_SYNC_ALL. This can greatly slow down umount,
since WB_SYNC_ALL writeback is a data integrity operation and thus
a bigger hammer than simple WB_SYNC_NONE. For barrier aware file systems
it's a lot slower.

Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent 69b62d01

fs/fs-writeback.c

+37 −11
Original line number Diff line number Diff line
@@ -45,6 +45,7 @@ struct wb_writeback_args { 
	int for_kupdate:1;

	int range_cyclic:1;

	int for_background:1;

	int sb_pinned:1;

};



/*
@@ -230,6 +231,11 @@ static void bdi_sync_writeback(struct backing_dev_info *bdi, 
		.sync_mode	= WB_SYNC_ALL,

		.nr_pages	= LONG_MAX,

		.range_cyclic	= 0,

		/*

		 * Setting sb_pinned is not necessary for WB_SYNC_ALL, but

		 * lets make it explicitly clear.

		 */

		.sb_pinned	= 1,

	};

	struct bdi_work work;
@@ -245,21 +251,23 @@ static void bdi_sync_writeback(struct backing_dev_info *bdi, 
 * @bdi: the backing device to write from

 * @sb: write inodes from this super_block

 * @nr_pages: the number of pages to write

 * @sb_locked: caller already holds sb umount sem.

 *

 * Description:

 *   This does WB_SYNC_NONE opportunistic writeback. The IO is only

 *   started when this function returns, we make no guarentees on

 *   completion. Caller need not hold sb s_umount semaphore.

 *   completion. Caller specifies whether sb umount sem is held already or not.

 *

 */

void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,

			 long nr_pages)

			 long nr_pages, int sb_locked)

{

	struct wb_writeback_args args = {

		.sb		= sb,

		.sync_mode	= WB_SYNC_NONE,

		.nr_pages	= nr_pages,

		.range_cyclic	= 1,

		.sb_pinned	= sb_locked,

	};



	/*
@@ -577,7 +585,7 @@ static enum sb_pin_state pin_sb_for_writeback(struct writeback_control *wbc, 
	/*

	 * Caller must already hold the ref for this

	 */

	if (wbc->sync_mode == WB_SYNC_ALL) {

	if (wbc->sync_mode == WB_SYNC_ALL || wbc->sb_pinned) {

		WARN_ON(!rwsem_is_locked(&sb->s_umount));

		return SB_NOT_PINNED;

	}
@@ -751,6 +759,7 @@ static long wb_writeback(struct bdi_writeback *wb, 
		.for_kupdate		= args->for_kupdate,

		.for_background		= args->for_background,

		.range_cyclic		= args->range_cyclic,

		.sb_pinned		= args->sb_pinned,

	};

	unsigned long oldest_jif;

	long wrote = 0;
@@ -1193,6 +1202,18 @@ static void wait_sb_inodes(struct super_block *sb) 
	iput(old_inode);

}



static void __writeback_inodes_sb(struct super_block *sb, int sb_locked)

{

	unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);

	unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);

	long nr_to_write;



	nr_to_write = nr_dirty + nr_unstable +

			(inodes_stat.nr_inodes - inodes_stat.nr_unused);



	bdi_start_writeback(sb->s_bdi, sb, nr_to_write, sb_locked);

}



/**

 * writeback_inodes_sb	-	writeback dirty inodes from given super_block

 * @sb: the superblock
@@ -1204,17 +1225,22 @@ static void wait_sb_inodes(struct super_block *sb) 
 */

void writeback_inodes_sb(struct super_block *sb)

{

	unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);

	unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);

	long nr_to_write;



	nr_to_write = nr_dirty + nr_unstable +

			(inodes_stat.nr_inodes - inodes_stat.nr_unused);



	bdi_start_writeback(sb->s_bdi, sb, nr_to_write);

	__writeback_inodes_sb(sb, 0);

}

EXPORT_SYMBOL(writeback_inodes_sb);



/**

 * writeback_inodes_sb_locked	- writeback dirty inodes from given super_block

 * @sb: the superblock

 *

 * Like writeback_inodes_sb(), except the caller already holds the

 * sb umount sem.

 */

void writeback_inodes_sb_locked(struct super_block *sb)

{

	__writeback_inodes_sb(sb, 1);

}



/**

 * writeback_inodes_sb_if_idle	-	start writeback if none underway

 * @sb: the superblock

fs/sync.c

+1 −1
Original line number Diff line number Diff line
@@ -42,7 +42,7 @@ static int __sync_filesystem(struct super_block *sb, int wait) 
	if (wait)

		sync_inodes_sb(sb);

	else

		writeback_inodes_sb(sb);

		writeback_inodes_sb_locked(sb);



	if (sb->s_op->sync_fs)

		sb->s_op->sync_fs(sb, wait);

include/linux/backing-dev.h

+1 −1
Original line number Diff line number Diff line
@@ -106,7 +106,7 @@ int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev); 
void bdi_unregister(struct backing_dev_info *bdi);

int bdi_setup_and_register(struct backing_dev_info *, char *, unsigned int);

void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,

				long nr_pages);

				long nr_pages, int sb_locked);

int bdi_writeback_task(struct bdi_writeback *wb);

int bdi_has_dirty_io(struct backing_dev_info *bdi);

include/linux/writeback.h

+10 −0
Original line number Diff line number Diff line
@@ -65,6 +65,15 @@ struct writeback_control { 
	 * so we use a single control to update them

	 */

	unsigned no_nrwrite_index_update:1;



	/*

	 * For WB_SYNC_ALL, the sb must always be pinned. For WB_SYNC_NONE,

	 * the writeback code will pin the sb for the caller. However,

	 * for eg umount, the caller does WB_SYNC_NONE but already has

	 * the sb pinned. If the below is set, caller already has the

	 * sb pinned.

	 */

	unsigned sb_pinned:1;

};



/*
@@ -73,6 +82,7 @@ struct writeback_control { 
struct bdi_writeback;

int inode_wait(void *);

void writeback_inodes_sb(struct super_block *);

void writeback_inodes_sb_locked(struct super_block *);

int writeback_inodes_sb_if_idle(struct super_block *);

void sync_inodes_sb(struct super_block *);

void writeback_inodes_wbc(struct writeback_control *wbc);

mm/page-writeback.c

+2 −2
Original line number Diff line number Diff line
@@ -597,7 +597,7 @@ static void balance_dirty_pages(struct address_space *mapping, 
	    (!laptop_mode && ((global_page_state(NR_FILE_DIRTY)

			       + global_page_state(NR_UNSTABLE_NFS))

					  > background_thresh)))

		bdi_start_writeback(bdi, NULL, 0);

		bdi_start_writeback(bdi, NULL, 0, 0);

}



void set_page_dirty_balance(struct page *page, int page_mkwrite)
@@ -705,7 +705,7 @@ void laptop_mode_timer_fn(unsigned long data) 
	 */



	if (bdi_has_dirty_io(&q->backing_dev_info))

		bdi_start_writeback(&q->backing_dev_info, NULL, nr_pages);

		bdi_start_writeback(&q->backing_dev_info, NULL, 0, nr_pages);

}



/*

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