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Commit b31dc66a authored by Jens Axboe's avatar Jens Axboe Committed by Jens Axboe
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[PATCH] Kill PF_SYNCWRITE flag 



A process flag to indicate whether we are doing sync io is incredibly
ugly. It also causes performance problems when one does a lot of async
io and then proceeds to sync it. Part of the io will go out as async,
and the other part as sync. This causes a disconnect between the
previously submitted io and the synced io. For io schedulers such as CFQ,
this will cause us lost merges and suboptimal behaviour in scheduling.

Remove PF_SYNCWRITE completely from the fsync/msync paths, and let
the O_DIRECT path just directly indicate that the writes are sync
by using WRITE_SYNC instead.

Signed-off-by: default avatarJens Axboe <axboe@suse.de>
parent 271f18f1

block/as-iosched.c

+1 −1
Original line number Diff line number Diff line
@@ -1339,7 +1339,7 @@ static void as_add_request(request_queue_t *q, struct request *rq) 
	arq->state = AS_RQ_NEW;



	if (rq_data_dir(arq->request) == READ

			|| current->flags&PF_SYNCWRITE)

			|| (arq->request->flags & REQ_RW_SYNC))

		arq->is_sync = 1;

	else

		arq->is_sync = 0;

block/cfq-iosched.c

+1 −3
Original line number Diff line number Diff line
@@ -277,8 +277,6 @@ static struct cfq_queue *cfq_find_cfq_hash(struct cfq_data *, unsigned int, unsi 
static void cfq_dispatch_insert(request_queue_t *, struct cfq_rq *);

static struct cfq_queue *cfq_get_queue(struct cfq_data *cfqd, unsigned int key, struct task_struct *tsk, gfp_t gfp_mask);



#define process_sync(tsk)	((tsk)->flags & PF_SYNCWRITE)



/*

 * lots of deadline iosched dupes, can be abstracted later...

 */
@@ -334,7 +332,7 @@ static int cfq_queue_empty(request_queue_t *q) 


static inline pid_t cfq_queue_pid(struct task_struct *task, int rw)

{

	if (rw == READ || process_sync(task))

	if (rw == READ || rw == WRITE_SYNC)

		return task->pid;



	return CFQ_KEY_ASYNC;

block/ll_rw_blk.c

+3 −0
Original line number Diff line number Diff line
@@ -2827,6 +2827,9 @@ static void init_request_from_bio(struct request *req, struct bio *bio) 
	if (unlikely(bio_barrier(bio)))

		req->flags |= (REQ_HARDBARRIER | REQ_NOMERGE);



	if (bio_sync(bio))

		req->flags |= REQ_RW_SYNC;



	req->errors = 0;

	req->hard_sector = req->sector = bio->bi_sector;

	req->hard_nr_sectors = req->nr_sectors = bio_sectors(bio);

drivers/usb/gadget/file_storage.c

+0 −2
Original line number Diff line number Diff line
@@ -1906,7 +1906,6 @@ static int fsync_sub(struct lun *curlun) 


	inode = filp->f_dentry->d_inode;

	mutex_lock(&inode->i_mutex);

	current->flags |= PF_SYNCWRITE;

	rc = filemap_fdatawrite(inode->i_mapping);

	err = filp->f_op->fsync(filp, filp->f_dentry, 1);

	if (!rc)
@@ -1914,7 +1913,6 @@ static int fsync_sub(struct lun *curlun) 
	err = filemap_fdatawait(inode->i_mapping);

	if (!rc)

		rc = err;

	current->flags &= ~PF_SYNCWRITE;

	mutex_unlock(&inode->i_mutex);

	VLDBG(curlun, "fdatasync -> %d\n", rc);

	return rc;

fs/buffer.c

+0 −2
Original line number Diff line number Diff line
@@ -331,7 +331,6 @@ long do_fsync(struct file *file, int datasync) 
		goto out;

	}



	current->flags |= PF_SYNCWRITE;

	ret = filemap_fdatawrite(mapping);



	/*
@@ -346,7 +345,6 @@ long do_fsync(struct file *file, int datasync) 
	err = filemap_fdatawait(mapping);

	if (!ret)

		ret = err;

	current->flags &= ~PF_SYNCWRITE;

out:

	return ret;

}