[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>

1 files changed, 5 insertions, 6 deletions

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 */
 
 /*