From: Mikulas Patocka <mpatocka redhat com>
To: Mike Snitzer <msnitzer redhat com>, Nikhil Kshirsagar <nkshirsa
redhat com>
Cc: dm-devel redhat com
Subject: [PATCH] dm-writecache: improve performance of large
linear writes on SSDs
Date: Wed, 15 Jan 2020 04:35:22 -0500 (EST)
When dm-writecache is used with SSD as a cache device, it would submit
separate bio for each written block. The I/Os would be merged by the disk
scheduler, but this merging degrades performance.
This patch makes dm-writecache submit larger bios - we can submit large
bio as long as there is consecutive free space on the cache device.
Benchmark (arm64 with 64k page size, using /dev/ram0 as a cache device):
fio --bs=512k --iodepth=32 --size=400M --direct=1
--filename=/dev/mapper/cache --rw=randwrite --numjobs=1 --name=test
block old new
size MiB/s MiB/s
---------------------
512 181 700
1k 347 1256
2k 644 2020
4k 1183 2759
8k 1852 3333
16k 2469 3509
32k 2974 3670
64k 3404 3810
Signed-off-by: Mikulas Patocka <mpatocka redhat com>
---
drivers/md/dm-writecache.c | 28 ++++++++++++++++++++++++----
1 file changed, 24 insertions(+), 4 deletions(-)
Index: linux-2.6/drivers/md/dm-writecache.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-writecache.c 2020-01-14
16:11:09.000000000 +0100
+++ linux-2.6/drivers/md/dm-writecache.c 2020-01-14
21:42:44.000000000 +0100
@@ -626,7 +626,7 @@ static void writecache_add_to_freelist(s
wc->freelist_size++;
}
-static struct wc_entry *writecache_pop_from_freelist(struct
dm_writecache *wc)
+static struct wc_entry *writecache_pop_from_freelist(struct
dm_writecache *wc, sector_t expected_sector)
{
struct wc_entry *e;
@@ -635,6 +635,8 @@ static struct wc_entry *writecache_pop_f
if (unlikely(!wc->current_free))
return NULL;
e = wc->current_free;
+ if (expected_sector != (sector_t)-1 &&
unlikely(cache_sector(wc, e) != expected_sector))
+ return NULL;
next = rb_next(&e->rb_node);
rb_erase(&e->rb_node, &wc->freetree);
if (unlikely(!next))
@@ -644,6 +646,8 @@ static struct wc_entry *writecache_pop_f
if (unlikely(list_empty(&wc->freelist)))
return NULL;
e = container_of(wc->freelist.next, struct wc_entry, lru);
+ if (expected_sector != (sector_t)-1 &&
unlikely(cache_sector(wc, e) != expected_sector))
+ return NULL;
list_del(&e->lru);
}
wc->freelist_size--;
@@ -1194,7 +1198,7 @@ read_next_block:
goto bio_copy;
}
}
- e = writecache_pop_from_freelist(wc);
+ e = writecache_pop_from_freelist(wc, (sector_t)-1);
if (unlikely(!e)) {
writecache_wait_on_freelist(wc);
continue;
@@ -1206,9 +1210,25 @@ bio_copy:
if (WC_MODE_PMEM(wc)) {
bio_copy_block(wc, bio, memory_data(wc, e));
} else {
- dm_accept_partial_bio(bio, wc->block_size >>
SECTOR_SHIFT);
+ unsigned bio_size = wc->block_size;
+ sector_t start_cache_sec = cache_sector(wc, e);
+ sector_t current_cache_sec = start_cache_sec +
(bio_size >> SECTOR_SHIFT);
+
+ while (bio_size < bio->bi_iter.bi_size) {
+ struct wc_entry *f =
writecache_pop_from_freelist(wc, current_cache_sec);
+ if (!f)
+ break;
+ write_original_sector_seq_count(wc, f,
bio->bi_iter.bi_sector + (bio_size >> SECTOR_SHIFT), wc->seq_count);
+ writecache_insert_entry(wc, f);
+ wc->uncommitted_blocks++;
+ bio_size += wc->block_size;
+ current_cache_sec += wc->block_size >> SECTOR_SHIFT;
+ }
+
bio_set_dev(bio, wc->ssd_dev->bdev);
- bio->bi_iter.bi_sector = cache_sector(wc, e);
+ bio->bi_iter.bi_sector = start_cache_sec;
+ dm_accept_partial_bio(bio, bio_size >> SECTOR_SHIFT);
+
if (unlikely(wc->uncommitted_blocks >=
wc->autocommit_blocks)) {
wc->uncommitted_blocks = 0;
queue_work(wc->writeback_wq, &wc->flush_work);
