On 2015/6/15 21:03, Ilya Dryomov wrote:
On Mon, Jun 15, 2015 at 2:18 PM, juncheng bai
<baijuncheng@xxxxxxxxxxxxxxx> wrote:
From 6213215bd19926d1063d4e01a248107dab8a899b Mon Sep 17 00:00:00 2001
From: juncheng bai <baijuncheng@xxxxxxxxxxxxxxx>
Date: Mon, 15 Jun 2015 18:34:00 +0800
Subject: [PATCH] storage:rbd: make the size of request is equal to the
size of the object
ensures that the merged size of request can achieve the size of
the object.
when merge a bio to request or merge a request to request, the
sum of the segment number of the current request and the segment
number of the bio is not greater than the max segments of the request,
so the max size of request is 512k if the max segments of request is
BLK_MAX_SEGMENTS.
Signed-off-by: juncheng bai <baijuncheng@xxxxxxxxxxxxxxx>
---
drivers/block/rbd.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 0a54c58..dec6045 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -3757,6 +3757,8 @@ static int rbd_init_disk(struct rbd_device *rbd_dev)
segment_size = rbd_obj_bytes(&rbd_dev->header);
blk_queue_max_hw_sectors(q, segment_size / SECTOR_SIZE);
blk_queue_max_segment_size(q, segment_size);
+ if (segment_size > BLK_MAX_SEGMENTS * PAGE_SIZE)
+ blk_queue_max_segments(q, segment_size / PAGE_SIZE);
blk_queue_io_min(q, segment_size);
blk_queue_io_opt(q, segment_size);
I made a similar patch on Friday, investigating blk-mq plugging issue
reported by Nick. My patch sets it to BIO_MAX_PAGES unconditionally -
AFAIU there is no point in setting to anything bigger since the bios
will be clipped to that number of vecs. Given that BIO_MAX_PAGES is
256, this gives is 1M direct I/Os.
Hi. For signal bio, the max number of bio_vec is BIO_MAX_PAGES, but a
request can be merged from multiple bios. We can see the below function:
ll_back_merge_fn, ll_front_merge_fn and etc.
And I test in kernel 3.18 use this patch, and do:
echo 4096 > /sys/block/rbd0/queue/max_sectors_kb
We use systemtap to trace the request size, It is upto 4M.
Thanks.
---------
juncheng bai
Thanks,
Ilya
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