[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 a9d23c7d1b2..38b4791e6a5 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 */
 
 /*