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. 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, so I added an option to
control it.
Signed-off-by: Shaohua Li <shli@xxxxxxxxxxxx>
---
drivers/md/raid5.c | 92 +++++++++++++++++++++++++++++++++++++++++++++--------
drivers/md/raid5.h | 4 +-
2 files changed, 82 insertions(+), 14 deletions(-)
Index: linux/drivers/md/raid5.c
===================================================================
--- linux.orig/drivers/md/raid5.c 2014-04-28 14:02:18.025349590 +0800
+++ linux/drivers/md/raid5.c 2014-04-28 14:02:18.009349792 +0800
@@ -479,6 +479,7 @@ static void shrink_buffers(struct stripe
int num = sh->raid_conf->pool_size;
for (i = 0; i < num ; i++) {
+ BUG_ON(sh->dev[i].page != sh->dev[i].orig_page);
p = sh->dev[i].page;
if (!p)
continue;
@@ -499,6 +500,7 @@ static int grow_buffers(struct stripe_he
return 1;
}
sh->dev[i].page = page;
+ sh->dev[i].orig_page = page;
}
return 0;
}
@@ -855,6 +857,9 @@ static void ops_run_io(struct stripe_hea
if (test_bit(R5_ReadNoMerge, &sh->dev[i].flags))
bi->bi_rw |= REQ_NOMERGE;
+ if (test_bit(R5_SkipCopy, &sh->dev[i].flags))
+ BUG_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;
@@ -899,6 +904,9 @@ static void ops_run_io(struct stripe_hea
else
rbi->bi_iter.bi_sector = (sh->sector
+ rrdev->data_offset);
+ if (test_bit(R5_SkipCopy, &sh->dev[i].flags))
+ BUG_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;
@@ -927,8 +935,9 @@ static void ops_run_io(struct stripe_hea
}
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;
@@ -965,11 +974,16 @@ async_copy_data(int frombio, struct bio
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 */
@@ -1045,8 +1059,8 @@ static void ops_run_biofill(struct strip
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);
}
}
@@ -1384,6 +1398,7 @@ ops_run_biodrain(struct stripe_head *sh,
BUG_ON(dev->written);
wbi = dev->written = chosen;
spin_unlock_irq(&sh->stripe_lock);
+ BUG_ON(dev->page != dev->orig_page);
while (wbi && wbi->bi_iter.bi_sector <
dev->sector + STRIPE_SECTORS) {
@@ -1393,9 +1408,15 @@ ops_run_biodrain(struct stripe_head *sh,
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);
}
}
@@ -1426,7 +1447,7 @@ static void ops_complete_reconstruct(voi
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);
@@ -2750,6 +2771,11 @@ handle_failed_stripe(struct r5conf *conf
/* 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)) {
+ BUG_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) {
@@ -2991,12 +3017,17 @@ static void handle_stripe_clean_event(st
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)) {
+ BUG_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 <
@@ -3015,6 +3046,8 @@ static void handle_stripe_clean_event(st
0);
} else if (test_bit(R5_Discard, &dev->flags))
discard_pending = 1;
+ BUG_ON(test_bit(R5_SkipCopy, &dev->flags));
+ BUG_ON(dev->page != dev->orig_page);
}
if (!discard_pending &&
test_bit(R5_Discard, &sh->dev[sh->pd_idx].flags)) {
@@ -5355,6 +5388,38 @@ raid5_preread_bypass_threshold = __ATTR(
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;
+ conf->skip_copy = new;
+ 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;
@@ -5439,6 +5504,7 @@ static struct attribute *raid5_attrs[] =
&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 = {
Index: linux/drivers/md/raid5.h
===================================================================
--- linux.orig/drivers/md/raid5.h 2014-04-28 14:02:18.025349590 +0800
+++ linux/drivers/md/raid5.h 2014-04-28 14:02:18.009349792 +0800
@@ -232,7 +232,7 @@ struct stripe_head {
*/
struct bio req, rreq;
struct bio_vec vec, rvec;
- struct page *page;
+ struct page *page, *orig_page;
struct bio *toread, *read, *towrite, *written;
sector_t sector; /* sector of this page */
unsigned long flags;
@@ -299,6 +299,7 @@ enum r5dev_flags {
* data in, and now is a good time to write it out.
*/
R5_Discard, /* Discard the stripe */
+ R5_SkipCopy, /* Don't copy data from bio to stripe cache */
};
/*
@@ -436,6 +437,7 @@ struct r5conf {
atomic_t pending_full_writes; /* full write backlog */
int bypass_count; /* bypassed prereads */
int bypass_threshold; /* preread nice */
+ int skip_copy; /* Don't copy data from bio to stripe cache */
struct list_head *last_hold; /* detect hold_list promotions */
atomic_t reshape_stripes; /* stripes with pending writes for reshape */
--
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