raid5: add an option to avoid copy data from bio to stripe cache
The stripe cache has two goals:
1. cache data, so next time if data can be found in stripe cache, disk access
can be avoided.
2. stable data. data is copied from bio to stripe cache and calculated parity.
data written to disk is from stripe cache, so if upper layer changes bio data,
data written to disk isn't impacted.
In my environment, I can guarantee 2 will not happen. And BDI_CAP_STABLE_WRITES
can guarantee 2 too. For 1, it's not common too. block plug mechanism will
dispatch a bunch of sequentail small requests together. And since I'm using
SSD, I'm using small chunk size. It's rare case stripe cache is really useful.
So I'd like to avoid the copy from bio to stripe cache and it's very helpful
for performance. In my 1M randwrite tests, avoid the copy can increase the
performance more than 30%.
Of course, this shouldn't be enabled by default. It's reported enabling
BDI_CAP_STABLE_WRITES can harm some workloads before, so I added an option to
control it.
Neilb:
changed BUG_ON to WARN_ON
Removed some assignments from raid5_build_block which are now not needed.
Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 348a857..d69fd98 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -487,6 +487,7 @@
int num = sh->raid_conf->pool_size;
for (i = 0; i < num ; i++) {
+ WARN_ON(sh->dev[i].page != sh->dev[i].orig_page);
p = sh->dev[i].page;
if (!p)
continue;
@@ -507,6 +508,7 @@
return 1;
}
sh->dev[i].page = page;
+ sh->dev[i].orig_page = page;
}
return 0;
}
@@ -863,6 +865,9 @@
if (test_bit(R5_ReadNoMerge, &sh->dev[i].flags))
bi->bi_rw |= REQ_NOMERGE;
+ if (test_bit(R5_SkipCopy, &sh->dev[i].flags))
+ WARN_ON(test_bit(R5_UPTODATE, &sh->dev[i].flags));
+ sh->dev[i].vec.bv_page = sh->dev[i].page;
bi->bi_vcnt = 1;
bi->bi_io_vec[0].bv_len = STRIPE_SIZE;
bi->bi_io_vec[0].bv_offset = 0;
@@ -907,6 +912,9 @@
else
rbi->bi_iter.bi_sector = (sh->sector
+ rrdev->data_offset);
+ if (test_bit(R5_SkipCopy, &sh->dev[i].flags))
+ WARN_ON(test_bit(R5_UPTODATE, &sh->dev[i].flags));
+ sh->dev[i].rvec.bv_page = sh->dev[i].page;
rbi->bi_vcnt = 1;
rbi->bi_io_vec[0].bv_len = STRIPE_SIZE;
rbi->bi_io_vec[0].bv_offset = 0;
@@ -935,8 +943,9 @@
}
static struct dma_async_tx_descriptor *
-async_copy_data(int frombio, struct bio *bio, struct page *page,
- sector_t sector, struct dma_async_tx_descriptor *tx)
+async_copy_data(int frombio, struct bio *bio, struct page **page,
+ sector_t sector, struct dma_async_tx_descriptor *tx,
+ struct stripe_head *sh)
{
struct bio_vec bvl;
struct bvec_iter iter;
@@ -973,11 +982,16 @@
if (clen > 0) {
b_offset += bvl.bv_offset;
bio_page = bvl.bv_page;
- if (frombio)
- tx = async_memcpy(page, bio_page, page_offset,
+ if (frombio) {
+ if (sh->raid_conf->skip_copy &&
+ b_offset == 0 && page_offset == 0 &&
+ clen == STRIPE_SIZE)
+ *page = bio_page;
+ else
+ tx = async_memcpy(*page, bio_page, page_offset,
b_offset, clen, &submit);
- else
- tx = async_memcpy(bio_page, page, b_offset,
+ } else
+ tx = async_memcpy(bio_page, *page, b_offset,
page_offset, clen, &submit);
}
/* chain the operations */
@@ -1053,8 +1067,8 @@
spin_unlock_irq(&sh->stripe_lock);
while (rbi && rbi->bi_iter.bi_sector <
dev->sector + STRIPE_SECTORS) {
- tx = async_copy_data(0, rbi, dev->page,
- dev->sector, tx);
+ tx = async_copy_data(0, rbi, &dev->page,
+ dev->sector, tx, sh);
rbi = r5_next_bio(rbi, dev->sector);
}
}
@@ -1392,6 +1406,7 @@
BUG_ON(dev->written);
wbi = dev->written = chosen;
spin_unlock_irq(&sh->stripe_lock);
+ WARN_ON(dev->page != dev->orig_page);
while (wbi && wbi->bi_iter.bi_sector <
dev->sector + STRIPE_SECTORS) {
@@ -1401,9 +1416,15 @@
set_bit(R5_SyncIO, &dev->flags);
if (wbi->bi_rw & REQ_DISCARD)
set_bit(R5_Discard, &dev->flags);
- else
- tx = async_copy_data(1, wbi, dev->page,
- dev->sector, tx);
+ else {
+ tx = async_copy_data(1, wbi, &dev->page,
+ dev->sector, tx, sh);
+ if (dev->page != dev->orig_page) {
+ set_bit(R5_SkipCopy, &dev->flags);
+ clear_bit(R5_UPTODATE, &dev->flags);
+ clear_bit(R5_OVERWRITE, &dev->flags);
+ }
+ }
wbi = r5_next_bio(wbi, dev->sector);
}
}
@@ -1434,7 +1455,7 @@
struct r5dev *dev = &sh->dev[i];
if (dev->written || i == pd_idx || i == qd_idx) {
- if (!discard)
+ if (!discard && !test_bit(R5_SkipCopy, &dev->flags))
set_bit(R5_UPTODATE, &dev->flags);
if (fua)
set_bit(R5_WantFUA, &dev->flags);
@@ -1847,8 +1868,10 @@
osh = get_free_stripe(conf, hash);
unlock_device_hash_lock(conf, hash);
atomic_set(&nsh->count, 1);
- for(i=0; i<conf->pool_size; i++)
+ for(i=0; i<conf->pool_size; i++) {
nsh->dev[i].page = osh->dev[i].page;
+ nsh->dev[i].orig_page = osh->dev[i].page;
+ }
for( ; i<newsize; i++)
nsh->dev[i].page = NULL;
nsh->hash_lock_index = hash;
@@ -1904,6 +1927,7 @@
if (nsh->dev[i].page == NULL) {
struct page *p = alloc_page(GFP_NOIO);
nsh->dev[i].page = p;
+ nsh->dev[i].orig_page = p;
if (!p)
err = -ENOMEM;
}
@@ -2141,24 +2165,20 @@
}
static sector_t compute_blocknr(struct stripe_head *sh, int i, int previous);
-
+
static void raid5_build_block(struct stripe_head *sh, int i, int previous)
{
struct r5dev *dev = &sh->dev[i];
bio_init(&dev->req);
dev->req.bi_io_vec = &dev->vec;
- dev->req.bi_vcnt++;
- dev->req.bi_max_vecs++;
+ dev->req.bi_max_vecs = 1;
dev->req.bi_private = sh;
- dev->vec.bv_page = dev->page;
bio_init(&dev->rreq);
dev->rreq.bi_io_vec = &dev->rvec;
- dev->rreq.bi_vcnt++;
- dev->rreq.bi_max_vecs++;
+ dev->rreq.bi_max_vecs = 1;
dev->rreq.bi_private = sh;
- dev->rvec.bv_page = dev->page;
dev->flags = 0;
dev->sector = compute_blocknr(sh, i, previous);
@@ -2758,6 +2778,11 @@
/* and fail all 'written' */
bi = sh->dev[i].written;
sh->dev[i].written = NULL;
+ if (test_and_clear_bit(R5_SkipCopy, &sh->dev[i].flags)) {
+ WARN_ON(test_bit(R5_UPTODATE, &sh->dev[i].flags));
+ sh->dev[i].page = sh->dev[i].orig_page;
+ }
+
if (bi) bitmap_end = 1;
while (bi && bi->bi_iter.bi_sector <
sh->dev[i].sector + STRIPE_SECTORS) {
@@ -3002,12 +3027,17 @@
dev = &sh->dev[i];
if (!test_bit(R5_LOCKED, &dev->flags) &&
(test_bit(R5_UPTODATE, &dev->flags) ||
- test_bit(R5_Discard, &dev->flags))) {
+ test_bit(R5_Discard, &dev->flags) ||
+ test_bit(R5_SkipCopy, &dev->flags))) {
/* We can return any write requests */
struct bio *wbi, *wbi2;
pr_debug("Return write for disc %d\n", i);
if (test_and_clear_bit(R5_Discard, &dev->flags))
clear_bit(R5_UPTODATE, &dev->flags);
+ if (test_and_clear_bit(R5_SkipCopy, &dev->flags)) {
+ WARN_ON(test_bit(R5_UPTODATE, &dev->flags));
+ dev->page = dev->orig_page;
+ }
wbi = dev->written;
dev->written = NULL;
while (wbi && wbi->bi_iter.bi_sector <
@@ -3026,6 +3056,8 @@
0);
} else if (test_bit(R5_Discard, &dev->flags))
discard_pending = 1;
+ WARN_ON(test_bit(R5_SkipCopy, &dev->flags));
+ WARN_ON(dev->page != dev->orig_page);
}
if (!discard_pending &&
test_bit(R5_Discard, &sh->dev[sh->pd_idx].flags)) {
@@ -5366,6 +5398,50 @@
raid5_store_preread_threshold);
static ssize_t
+raid5_show_skip_copy(struct mddev *mddev, char *page)
+{
+ struct r5conf *conf = mddev->private;
+ if (conf)
+ return sprintf(page, "%d\n", conf->skip_copy);
+ else
+ return 0;
+}
+
+static ssize_t
+raid5_store_skip_copy(struct mddev *mddev, const char *page, size_t len)
+{
+ struct r5conf *conf = mddev->private;
+ unsigned long new;
+ if (len >= PAGE_SIZE)
+ return -EINVAL;
+ if (!conf)
+ return -ENODEV;
+
+ if (kstrtoul(page, 10, &new))
+ return -EINVAL;
+ new = !!new;
+ if (new == conf->skip_copy)
+ return len;
+
+ mddev_suspend(mddev);
+ conf->skip_copy = new;
+ if (new)
+ mddev->queue->backing_dev_info.capabilities |=
+ BDI_CAP_STABLE_WRITES;
+ else
+ mddev->queue->backing_dev_info.capabilities &=
+ ~BDI_CAP_STABLE_WRITES;
+ mddev_resume(mddev);
+ return len;
+}
+
+static struct md_sysfs_entry
+raid5_skip_copy = __ATTR(skip_copy, S_IRUGO | S_IWUSR,
+ raid5_show_skip_copy,
+ raid5_store_skip_copy);
+
+
+static ssize_t
stripe_cache_active_show(struct mddev *mddev, char *page)
{
struct r5conf *conf = mddev->private;
@@ -5450,6 +5526,7 @@
&raid5_stripecache_active.attr,
&raid5_preread_bypass_threshold.attr,
&raid5_group_thread_cnt.attr,
+ &raid5_skip_copy.attr,
NULL,
};
static struct attribute_group raid5_attrs_group = {