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md/raid56: Don't perform reads to support writes until stripe is ready.

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If it is found that we need to pre-read some blocks before a write
can succeed, we normally set STRIPE_DELAYED and don't actually perform
the read until STRIPE_PREREAD_ACTIVE subsequently gets set.

However for a degraded RAID6 we currently perform the reads as soon
as we see that a write is pending.  This significantly hurts
throughput.

So:
 - when handle_stripe_dirtying find a block that it wants on a device
   that is failed, set STRIPE_DELAY, instead of doing nothing, and
 - when fetch_block detects that a read might be required to satisfy a
   write, only perform the read if STRIPE_PREREAD_ACTIVE is set,
   and if we would actually need to read something to complete the write.

This also helps RAID5, though less often as RAID5 supports a
read-modify-write cycle.  For RAID5 the read is performed too early
only if the write is not a full 4K aligned write (i.e. no an
R5_OVERWRITE).

Also clean up a couple of horrible bits of formatting.

Reported-by: Patrik Horník <patrik@dsl.sk>
Signed-off-by: NeilBrown <neilb@suse.de>
This commit is contained in:
NeilBrown 2014-05-28 13:39:22 +10:00
parent bd8839e03b
commit 67f455486d
1 changed files with 18 additions and 12 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

30
drivers/md/raid5.c
View file

@ -292,9 +292,12 @@ static void do_release_stripe(struct r5conf *conf, struct stripe_head *sh,
BUG_ON(atomic_read(&conf->active_stripes)==0); BUG_ON(atomic_read(&conf->active_stripes)==0);
if (test_bit(STRIPE_HANDLE, &sh->state)) { if (test_bit(STRIPE_HANDLE, &sh->state)) {
if (test_bit(STRIPE_DELAYED, &sh->state) && if (test_bit(STRIPE_DELAYED, &sh->state) &&
!test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) !test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
list_add_tail(&sh->lru, &conf->delayed_list); list_add_tail(&sh->lru, &conf->delayed_list);
else if (test_bit(STRIPE_BIT_DELAY, &sh->state) && if (atomic_read(&conf->preread_active_stripes)
< IO_THRESHOLD)
md_wakeup_thread(conf->mddev->thread);
} else if (test_bit(STRIPE_BIT_DELAY, &sh->state) &&
sh->bm_seq - conf->seq_write > 0) sh->bm_seq - conf->seq_write > 0)
list_add_tail(&sh->lru, &conf->bitmap_list); list_add_tail(&sh->lru, &conf->bitmap_list);
else { else {
@ -2886,8 +2889,11 @@ static int fetch_block(struct stripe_head *sh, struct stripe_head_state *s,
(s->failed >= 1 && fdev[0]->toread) || (s->failed >= 1 && fdev[0]->toread) ||
(s->failed >= 2 && fdev[1]->toread) || (s->failed >= 2 && fdev[1]->toread) ||
(sh->raid_conf->level <= 5 && s->failed && fdev[0]->towrite && (sh->raid_conf->level <= 5 && s->failed && fdev[0]->towrite &&
(!test_bit(R5_Insync, &dev->flags) || test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) &&
!test_bit(R5_OVERWRITE, &fdev[0]->flags)) || !test_bit(R5_OVERWRITE, &fdev[0]->flags)) ||
(sh->raid_conf->level == 6 && s->failed && s->to_write))) { (sh->raid_conf->level == 6 && s->failed && s->to_write &&
s->to_write < sh->raid_conf->raid_disks - 2 &&
(!test_bit(R5_Insync, &dev->flags) || test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))))) {
/* we would like to get this block, possibly by computing it, /* we would like to get this block, possibly by computing it,
* otherwise read it if the backing disk is insync * otherwise read it if the backing disk is insync
*/ */
@ -3086,7 +3092,8 @@ static void handle_stripe_dirtying(struct r5conf *conf,
!test_bit(R5_LOCKED, &dev->flags) && !test_bit(R5_LOCKED, &dev->flags) &&
!(test_bit(R5_UPTODATE, &dev->flags) || !(test_bit(R5_UPTODATE, &dev->flags) ||
test_bit(R5_Wantcompute, &dev->flags))) { test_bit(R5_Wantcompute, &dev->flags))) {
if (test_bit(R5_Insync, &dev->flags)) rcw++; if (test_bit(R5_Insync, &dev->flags))
rcw++;
else else
rcw += 2*disks; rcw += 2*disks;
} }
@ -3107,10 +3114,10 @@ static void handle_stripe_dirtying(struct r5conf *conf,
!(test_bit(R5_UPTODATE, &dev->flags) || !(test_bit(R5_UPTODATE, &dev->flags) ||
test_bit(R5_Wantcompute, &dev->flags)) && test_bit(R5_Wantcompute, &dev->flags)) &&
test_bit(R5_Insync, &dev->flags)) { test_bit(R5_Insync, &dev->flags)) {
if ( if (test_bit(STRIPE_PREREAD_ACTIVE,
test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) { &sh->state)) {
pr_debug("Read_old block " pr_debug("Read_old block %d for r-m-w\n",
"%d for r-m-w\n", i); i);
set_bit(R5_LOCKED, &dev->flags); set_bit(R5_LOCKED, &dev->flags);
set_bit(R5_Wantread, &dev->flags); set_bit(R5_Wantread, &dev->flags);
s->locked++; s->locked++;
@ -3133,10 +3140,9 @@ static void handle_stripe_dirtying(struct r5conf *conf,
!(test_bit(R5_UPTODATE, &dev->flags) || !(test_bit(R5_UPTODATE, &dev->flags) ||
test_bit(R5_Wantcompute, &dev->flags))) { test_bit(R5_Wantcompute, &dev->flags))) {
rcw++; rcw++;
if (!test_bit(R5_Insync, &dev->flags)) if (test_bit(R5_Insync, &dev->flags) &&
continue; /* it's a failed drive */ test_bit(STRIPE_PREREAD_ACTIVE,
if ( &sh->state)) {
test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
pr_debug("Read_old block " pr_debug("Read_old block "
"%d for Reconstruct\n", i); "%d for Reconstruct\n", i);
set_bit(R5_LOCKED, &dev->flags); set_bit(R5_LOCKED, &dev->flags);