[md PATCH 06/14] md/raid5: remove over-loading of ->bi_phys_segments.

NeilBrown
2017-02-16T04:39:02Z

When a read request, which bypassed the cache, fails, we need to retry
it through the cache.
This involves attaching it to a sequence of stripe_heads, and it may not
be possible to get all the stripe_heads we need at once.
We do what we can, and record how far we got in ->bi_phys_segments so
we can pick up again later.

There is only ever one bio which may have a non-zero offset stored in
->bi_phys_segments, the one that is either active in the single thread
which calls retry_aligned_read(), or is in conf->retry_read_aligned
waiting for retry_aligned_read() to be called again.

So we only need to store one offset value. This can be in a local
variable passed between remove_bio_from_retry() and
retry_aligned_read(), or in the r5conf structure next to the
->retry_read_aligned pointer.

Storing it there allows the last usage of ->bi_phys_segments to be
removed from md/raid5.c.

Signed-off-by: NeilBrown <neilb@suse.com>
---
drivers/md/raid5.c | 24 ++++++++++++------------
drivers/md/raid5.h | 30 +-----------------------------
2 files changed, 13 insertions(+), 41 deletions(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 905abf081acf..f93e8fddbb23 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -4883,12 +4883,14 @@ static void add_bio_to_retry(struct bio *bi,struct r5conf *conf)
md_wakeup_thread(conf->mddev->thread);
}

-static struct bio *remove_bio_from_retry(struct r5conf *conf)
+static struct bio *remove_bio_from_retry(struct r5conf *conf,
+ unsigned int *offset)
{
struct bio *bi;

bi = conf->retry_read_aligned;
if (bi) {
+ *offset = conf->retry_read_offset;
conf->retry_read_aligned = NULL;
return bi;
}
@@ -4896,11 +4898,7 @@ static struct bio *remove_bio_from_retry(struct r5conf *conf)
if(bi) {
conf->retry_read_aligned_list = bi->bi_next;
bi->bi_next = NULL;
- /*
- * this sets the active strip count to 1 and the processed
- * strip count to zero (upper 8 bits)
- */
- raid5_set_bi_processed_stripes(bi, 0);
+ *offset = 0;
}

return bi;
@@ -5835,7 +5833,8 @@ static inline sector_t raid5_sync_request(struct mddev *mddev, sector_t sector_n
return STRIPE_SECTORS;
}

-static int retry_aligned_read(struct r5conf *conf, struct bio *raid_bio)
+static int retry_aligned_read(struct r5conf *conf, struct bio *raid_bio,
+ unsigned int offset)
{
/* We may not be able to submit a whole bio at once as there
* may not be enough stripe_heads available.
@@ -5864,7 +5863,7 @@ static int retry_aligned_read(struct r5conf *conf, struct bio *raid_bio)
sector += STRIPE_SECTORS,
scnt++) {

- if (scnt < raid5_bi_processed_stripes(raid_bio))
+ if (scnt < offset)
/* already done this stripe */
continue;

@@ -5872,15 +5871,15 @@ static int retry_aligned_read(struct r5conf *conf, struct bio *raid_bio)

if (!sh) {
/* failed to get a stripe - must wait */
- raid5_set_bi_processed_stripes(raid_bio, scnt);
conf->retry_read_aligned = raid_bio;
+ conf->retry_read_offset = scnt;
return handled;
}

if (!add_stripe_bio(sh, raid_bio, dd_idx, 0, 0)) {
raid5_release_stripe(sh);
- raid5_set_bi_processed_stripes(raid_bio, scnt);
conf->retry_read_aligned = raid_bio;
+ conf->retry_read_offset = scnt;
return handled;
}

@@ -6003,6 +6002,7 @@ static void raid5d(struct md_thread *thread)
while (1) {
struct bio *bio;
int batch_size, released;
+ unsigned int offset;

released = release_stripe_list(conf, conf->temp_inactive_list);
if (released)
@@ -6020,10 +6020,10 @@ static void raid5d(struct md_thread *thread)
}
raid5_activate_delayed(conf);

- while ((bio = remove_bio_from_retry(conf))) {
+ while ((bio = remove_bio_from_retry(conf, &offset))) {
int ok;
spin_unlock_irq(&conf->device_lock);
- ok = retry_aligned_read(conf, bio);
+ ok = retry_aligned_read(conf, bio, offset);
spin_lock_irq(&conf->device_lock);
if (!ok)
break;
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 3018a33693ab..a4ef02176afb 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -480,35 +480,6 @@ static inline struct bio *r5_next_bio(struct bio *bio, sector_t sector)
return NULL;
}

-/*
- * We maintain a count of processed stripes in the upper 16 bits
- */
-static inline int raid5_bi_processed_stripes(struct bio *bio)
-{
- atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
-
- return (atomic_read(segments) >> 16) & 0xffff;
-}
-
-static inline void raid5_set_bi_processed_stripes(struct bio *bio,
- unsigned int cnt)
-{
- atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
- int old, new;
-
- do {
- old = atomic_read(segments);
- new = (old & 0xffff) | (cnt << 16);
- } while (atomic_cmpxchg(segments, old, new) != old);
-}
-
-static inline void raid5_set_bi_stripes(struct bio *bio, unsigned int cnt)
-{
- atomic_t *segments = (atomic_t *)&bio->bi_phys_segments;
-
- atomic_set(segments, cnt);
-}
-
/* NOTE NR_STRIPE_HASH_LOCKS must remain below 64.
* This is because we sometimes take all the spinlocks
* and creating that much locking depth can cause
@@ -596,6 +567,7 @@ struct r5conf {
struct list_head delayed_list; /* stripes that have plugged requests */
struct list_head bitmap_list; /* stripes delaying awaiting bitmap update */
struct bio *retry_read_aligned; /* currently retrying aligned bios */
+ unsigned int retry_read_offset; /* sector offset into retry_read_aligned */
struct bio *retry_read_aligned_list; /* aligned bios retry list */
atomic_t preread_active_stripes; /* stripes with scheduled io */
atomic_t active_aligned_reads;