[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>

2 files changed, 7 insertions, 6 deletions

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 */
 
 /*