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MD: raid5 avoid unnecessary zero page for trim
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We want to avoid zero discarded dev page, because it's useless for discard.
But if we don't zero it, another read/write hit such page in the cache and will
get inconsistent data.

To avoid zero the page, we don't set R5_UPTODATE flag after construction is
done. In this way, discard write request is still issued and finished, but read
will not hit the page. If the stripe gets accessed soon, we need reread the
stripe, but since the chance is low, the reread isn't a big deal.

Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: NeilBrown <neilb@suse.de>
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Shaohua Li authored and NeilBrown committed Oct 11, 2012
1 parent 620125f commit 9e44476
Showing 1 changed file with 17 additions and 18 deletions.
35 changes: 17 additions & 18 deletions drivers/md/raid5.c
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Original file line number Diff line number Diff line change
Expand Up @@ -547,7 +547,7 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
rw = WRITE_FUA;
else
rw = WRITE;
if (test_and_clear_bit(R5_Discard, &sh->dev[i].flags))
if (test_bit(R5_Discard, &sh->dev[i].flags))
rw |= REQ_DISCARD;
} else if (test_and_clear_bit(R5_Wantread, &sh->dev[i].flags))
rw = READ;
Expand Down Expand Up @@ -1172,11 +1172,9 @@ ops_run_biodrain(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
set_bit(R5_WantFUA, &dev->flags);
if (wbi->bi_rw & REQ_SYNC)
set_bit(R5_SyncIO, &dev->flags);
if (wbi->bi_rw & REQ_DISCARD) {
memset(page_address(dev->page), 0,
STRIPE_SECTORS << 9);
if (wbi->bi_rw & REQ_DISCARD)
set_bit(R5_Discard, &dev->flags);
} else
else
tx = async_copy_data(1, wbi, dev->page,
dev->sector, tx);
wbi = r5_next_bio(wbi, dev->sector);
Expand All @@ -1194,21 +1192,23 @@ static void ops_complete_reconstruct(void *stripe_head_ref)
int pd_idx = sh->pd_idx;
int qd_idx = sh->qd_idx;
int i;
bool fua = false, sync = false;
bool fua = false, sync = false, discard = false;

pr_debug("%s: stripe %llu\n", __func__,
(unsigned long long)sh->sector);

for (i = disks; i--; ) {
fua |= test_bit(R5_WantFUA, &sh->dev[i].flags);
sync |= test_bit(R5_SyncIO, &sh->dev[i].flags);
discard |= test_bit(R5_Discard, &sh->dev[i].flags);
}

for (i = disks; i--; ) {
struct r5dev *dev = &sh->dev[i];

if (dev->written || i == pd_idx || i == qd_idx) {
set_bit(R5_UPTODATE, &dev->flags);
if (!discard)
set_bit(R5_UPTODATE, &dev->flags);
if (fua)
set_bit(R5_WantFUA, &dev->flags);
if (sync)
Expand Down Expand Up @@ -1252,8 +1252,6 @@ ops_run_reconstruct5(struct stripe_head *sh, struct raid5_percpu *percpu,
}
if (i >= sh->disks) {
atomic_inc(&sh->count);
memset(page_address(sh->dev[pd_idx].page), 0,
STRIPE_SECTORS << 9);
set_bit(R5_Discard, &sh->dev[pd_idx].flags);
ops_complete_reconstruct(sh);
return;
Expand Down Expand Up @@ -1314,10 +1312,6 @@ ops_run_reconstruct6(struct stripe_head *sh, struct raid5_percpu *percpu,
}
if (i >= sh->disks) {
atomic_inc(&sh->count);
memset(page_address(sh->dev[sh->pd_idx].page), 0,
STRIPE_SECTORS << 9);
memset(page_address(sh->dev[sh->qd_idx].page), 0,
STRIPE_SECTORS << 9);
set_bit(R5_Discard, &sh->dev[sh->pd_idx].flags);
set_bit(R5_Discard, &sh->dev[sh->qd_idx].flags);
ops_complete_reconstruct(sh);
Expand Down Expand Up @@ -2775,7 +2769,8 @@ static void handle_stripe_clean_event(struct r5conf *conf,
if (sh->dev[i].written) {
dev = &sh->dev[i];
if (!test_bit(R5_LOCKED, &dev->flags) &&
test_bit(R5_UPTODATE, &dev->flags)) {
(test_bit(R5_UPTODATE, &dev->flags) ||
test_and_clear_bit(R5_Discard, &dev->flags))) {
/* We can return any write requests */
struct bio *wbi, *wbi2;
pr_debug("Return write for disc %d\n", i);
Expand Down Expand Up @@ -3493,10 +3488,12 @@ static void handle_stripe(struct stripe_head *sh)
if (s.written &&
(s.p_failed || ((test_bit(R5_Insync, &pdev->flags)
&& !test_bit(R5_LOCKED, &pdev->flags)
&& test_bit(R5_UPTODATE, &pdev->flags)))) &&
&& (test_bit(R5_UPTODATE, &pdev->flags) ||
test_bit(R5_Discard, &pdev->flags))))) &&
(s.q_failed || ((test_bit(R5_Insync, &qdev->flags)
&& !test_bit(R5_LOCKED, &qdev->flags)
&& test_bit(R5_UPTODATE, &qdev->flags)))))
&& (test_bit(R5_UPTODATE, &qdev->flags) ||
test_bit(R5_Discard, &qdev->flags))))))
handle_stripe_clean_event(conf, sh, disks, &s.return_bi);

/* Now we might consider reading some blocks, either to check/generate
Expand All @@ -3523,9 +3520,11 @@ static void handle_stripe(struct stripe_head *sh)
/* All the 'written' buffers and the parity block are ready to
* be written back to disk
*/
BUG_ON(!test_bit(R5_UPTODATE, &sh->dev[sh->pd_idx].flags));
BUG_ON(!test_bit(R5_UPTODATE, &sh->dev[sh->pd_idx].flags) &&
!test_bit(R5_Discard, &sh->dev[sh->pd_idx].flags));
BUG_ON(sh->qd_idx >= 0 &&
!test_bit(R5_UPTODATE, &sh->dev[sh->qd_idx].flags));
!test_bit(R5_UPTODATE, &sh->dev[sh->qd_idx].flags) &&
!test_bit(R5_Discard, &sh->dev[sh->qd_idx].flags));
for (i = disks; i--; ) {
struct r5dev *dev = &sh->dev[i];
if (test_bit(R5_LOCKED, &dev->flags) &&
Expand Down

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