[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: Jens Axboe <axboe@suse.de>

10 files changed, 20 insertions, 29 deletions

diff --git a/block/as-iosched.c b/block/as-iosched.c
index 9b13d72ffefa..56c99fa037df 100644
--- a/block/as-iosched.c
+++ b/block/as-iosched.c
@@ -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;
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index c88f161d3fb3..4c4e9cc3ae26 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -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;
diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index 17c42ddd31db..2270bb451385 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -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);
diff --git a/drivers/usb/gadget/file_storage.c b/drivers/usb/gadget/file_storage.c
index 6f887478b148..a43dc908ac59 100644
--- a/drivers/usb/gadget/file_storage.c
+++ b/drivers/usb/gadget/file_storage.c
@@ -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;
diff --git a/fs/buffer.c b/fs/buffer.c
index 23f1f3a68077..373bb6292bdc 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -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;
 }
diff --git a/fs/direct-io.c b/fs/direct-io.c
index b05d1b218776..538fb0418fba 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -162,7 +162,7 @@ static int dio_refill_pages(struct dio *dio)
                 NULL);                          /* vmas */
         up_read(&current->mm->mmap_sem);
 
-        if (ret < 0 && dio->blocks_available && (dio->rw == WRITE)) {
+        if (ret < 0 && dio->blocks_available && (dio->rw & WRITE)) {
                 struct page *page = ZERO_PAGE(dio->curr_user_address);
                 /*
                  * A memory fault, but the filesystem has some outstanding
@@ -535,7 +535,7 @@ static int get_more_blocks(struct dio *dio)
                 map_bh->b_state = 0;
                 map_bh->b_size = fs_count << dio->inode->i_blkbits;
 
-                create = dio->rw == WRITE;
+                create = dio->rw & WRITE;
                 if (dio->lock_type == DIO_LOCKING) {
                         if (dio->block_in_file < (i_size_read(dio->inode) >>
                                                         dio->blkbits))
@@ -867,7 +867,7 @@ do_holes:
                                 loff_t i_size_aligned;
 
                                 /* AKPM: eargh, -ENOTBLK is a hack */
-                                if (dio->rw == WRITE) {
+                                if (dio->rw & WRITE) {
                                         page_cache_release(page);
                                         return -ENOTBLK;
                                 }
@@ -1045,7 +1045,7 @@ direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
                 }
         } /* end iovec loop */
 
-        if (ret == -ENOTBLK && rw == WRITE) {
+        if (ret == -ENOTBLK && (rw & WRITE)) {
                 /*
                  * The remaining part of the request will be
                  * be handled by buffered I/O when we return
@@ -1089,7 +1089,7 @@ direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
         if (dio->is_async) {
                 int should_wait = 0;
 
-                if (dio->result < dio->size && rw == WRITE) {
+                if (dio->result < dio->size && (rw & WRITE)) {
                         dio->waiter = current;
                         should_wait = 1;
                 }
@@ -1142,7 +1142,7 @@ direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
                         ret = transferred;
 
                 /* We could have also come here on an AIO file extend */
-                if (!is_sync_kiocb(iocb) && rw == WRITE &&
+                if (!is_sync_kiocb(iocb) && (rw & WRITE) &&
                     ret >= 0 && dio->result == dio->size)
                         /*
                          * For AIO writes where we have completed the
@@ -1194,7 +1194,7 @@ __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
         int acquire_i_mutex = 0;
 
         if (rw & WRITE)
-                current->flags |= PF_SYNCWRITE;
+                rw = WRITE_SYNC;
 
         if (bdev)
                 bdev_blkbits = blksize_bits(bdev_hardsect_size(bdev));
@@ -1270,7 +1270,7 @@ __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
          * even for AIO, we need to wait for i/o to complete before
          * returning in this case.
          */
-        dio->is_async = !is_sync_kiocb(iocb) && !((rw == WRITE) &&
+        dio->is_async = !is_sync_kiocb(iocb) && !((rw & WRITE) &&
                 (end > i_size_read(inode)));
 
         retval = direct_io_worker(rw, iocb, inode, iov, offset,
@@ -1284,8 +1284,6 @@ out:
                 mutex_unlock(&inode->i_mutex);
         else if (acquire_i_mutex)
                 mutex_lock(&inode->i_mutex);
-        if (rw & WRITE)
-                current->flags &= ~PF_SYNCWRITE;
         return retval;
 }
 EXPORT_SYMBOL(__blockdev_direct_IO);
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 6db95cf3aaa2..031b27a4bc9a 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -623,7 +623,6 @@ int generic_osync_inode(struct inode *inode, struct address_space *mapping, int
         int need_write_inode_now = 0;
         int err2;
 
-        current->flags |= PF_SYNCWRITE;
         if (what & OSYNC_DATA)
                 err = filemap_fdatawrite(mapping);
         if (what & (OSYNC_METADATA|OSYNC_DATA)) {
@@ -636,7 +635,6 @@ int generic_osync_inode(struct inode *inode, struct address_space *mapping, int
                 if (!err)
                         err = err2;
         }
-        current->flags &= ~PF_SYNCWRITE;
 
         spin_lock(&inode_lock);
         if ((inode->i_state & I_DIRTY) &&
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 3457e7b97363..482a21d67627 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -241,6 +241,7 @@ enum rq_flag_bits {
         __REQ_PM_RESUME,        /* resume request */
         __REQ_PM_SHUTDOWN,      /* shutdown request */
         __REQ_ORDERED_COLOR,    /* is before or after barrier */
+        __REQ_RW_SYNC,          /* request is sync (O_DIRECT) */
         __REQ_NR_BITS,          /* stops here */
 };
 
@@ -270,6 +271,7 @@ enum rq_flag_bits {
 #define REQ_PM_RESUME   (1 << __REQ_PM_RESUME)
 #define REQ_PM_SHUTDOWN (1 << __REQ_PM_SHUTDOWN)
 #define REQ_ORDERED_COLOR       (1 << __REQ_ORDERED_COLOR)
+#define REQ_RW_SYNC     (1 << __REQ_RW_SYNC)
 
 /*
  * State information carried for REQ_PM_SUSPEND and REQ_PM_RESUME
diff --git a/include/linux/sched.h b/include/linux/sched.h
index a9d23c7d1b25..38b4791e6a5d 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -941,12 +941,11 @@ static inline void put_task_struct(struct task_struct *t)
 #define PF_KSWAPD       0x00040000      /* I am kswapd */
 #define PF_SWAPOFF      0x00080000      /* I am in swapoff */
 #define PF_LESS_THROTTLE 0x00100000     /* Throttle me less: I clean memory */
-#define PF_SYNCWRITE    0x00200000      /* I am doing a sync write */
-#define PF_BORROWED_MM  0x00400000      /* I am a kthread doing use_mm */
-#define PF_RANDOMIZE    0x00800000      /* randomize virtual address space */
-#define PF_SWAPWRITE    0x01000000      /* Allowed to write to swap */
-#define PF_SPREAD_PAGE  0x04000000      /* Spread page cache over cpuset */
-#define PF_SPREAD_SLAB  0x08000000      /* Spread some slab caches over cpuset */
+#define PF_BORROWED_MM  0x00200000      /* I am a kthread doing use_mm */
+#define PF_RANDOMIZE    0x00400000      /* randomize virtual address space */
+#define PF_SWAPWRITE    0x00800000      /* Allowed to write to swap */
+#define PF_SPREAD_PAGE  0x01000000      /* Spread page cache over cpuset */
+#define PF_SPREAD_SLAB  0x02000000      /* Spread some slab caches over cpuset */
 #define PF_MEMPOLICY    0x10000000      /* Non-default NUMA mempolicy */
 
 /*
diff --git a/mm/msync.c b/mm/msync.c
index bc6c95376366..d083544df21b 100644
--- a/mm/msync.c
+++ b/mm/msync.c
@@ -170,8 +170,6 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
          * just ignore them, but return -ENOMEM at the end.
          */
         down_read(&current->mm->mmap_sem);
-        if (flags & MS_SYNC)
-                current->flags |= PF_SYNCWRITE;
         vma = find_vma(current->mm, start);
         if (!vma) {
                 error = -ENOMEM;
@@ -228,7 +226,6 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
                 }
         } while (vma && !done);
 out_unlock:
-        current->flags &= ~PF_SYNCWRITE;
         up_read(&current->mm->mmap_sem);
 out:
         return error;