Re: [patch]raid5: fix directio regression

["Jianpeng Ma" <majianpeng@gmail.com>]

On 2012-08-07 11:22 Shaohua Li <shli@kernel.org> Wrote:
>My directIO randomwrite 4k workload shows a 10~20% regression caused by commit
>895e3c5c58a80bb. directIO usually is random IO and if request size isn't big
>(which is the common case), delay handling of the stripe hasn't any advantages.
>For big size request, delay can still reduce IO.
>
>Signed-off-by: Shaohua Li <shli@fusionio.com>
>---
> drivers/md/raid5.c |    9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
>Index: linux/drivers/md/raid5.c
>===================================================================
>--- linux.orig/drivers/md/raid5.c	2012-08-07 11:04:48.442834682 +0800
>+++ linux/drivers/md/raid5.c	2012-08-07 11:09:08.743562203 +0800
>@@ -4076,6 +4076,7 @@ static void make_request(struct mddev *m
> 	struct stripe_head *sh;
> 	const int rw = bio_data_dir(bi);
> 	int remaining;
>+	bool large_request;
> 
> 	if (unlikely(bi->bi_rw & REQ_FLUSH)) {
> 		md_flush_request(mddev, bi);
>@@ -4089,6 +4090,11 @@ static void make_request(struct mddev *m
> 	     chunk_aligned_read(mddev,bi))
> 		return;
> 
>+	if (mddev->new_chunk_sectors < mddev->chunk_sectors)
>+		large_request = (bi->bi_size >> 9) > mddev->new_chunk_sectors;
>+	else
>+		large_request = (bi->bi_size >> 9) > mddev->chunk_sectors;
>+
> 	logical_sector = bi->bi_sector & ~((sector_t)STRIPE_SECTORS-1);
> 	last_sector = bi->bi_sector + (bi->bi_size>>9);
> 	bi->bi_next = NULL;
>@@ -4192,7 +4198,8 @@ static void make_request(struct mddev *m
> 			finish_wait(&conf->wait_for_overlap, &w);
> 			set_bit(STRIPE_HANDLE, &sh->state);
> 			clear_bit(STRIPE_DELAYED, &sh->state);
>-			if ((bi->bi_rw & REQ_NOIDLE) &&
>+			if ((bi->bi_rw & REQ_SYNC) &&
>+			    ((bi->bi_rw & REQ_NOIDLE) || !large_request) &&
> 			    !test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
> 				atomic_inc(&conf->preread_active_stripes);
> 			release_stripe_plug(mddev, sh);
>--
May be used size to judge is not a good method.
I firstly sended this patch, only want to control direct-write-block,not for reqular file.
Because i think if someone used direct-write-block for raid5,he should know the feature of raid5 and he can control
for write to full-write. 
But at that time, i did know how to differentiate between regular file and block-device.
I thik we should do something to do this.