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md/raid5: remove over-loading of ->bi_phys_segments. 

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>
Signed-off-by: Shaohua Li <shli@fb.com>
This commit is contained in:
NeilBrown 2017-03-15 14:05:13 +11:00 committed by Shaohua Li
parent 016c76ac76
commit 0472a42ba1
2 changed files with 13 additions and 41 deletions
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24
drivers/md/raid5.c
View File

@ -5082,12 +5082,14 @@ 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;
}
@ -5095,11 +5097,7 @@ 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;
@ -6055,7 +6053,8 @@ 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.
@ -6084,7 +6083,7 @@ 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;
@ -6092,15 +6091,15 @@ 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;
}
@ -6228,6 +6227,7 @@ 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)
@ -6245,10 +6245,10 @@ 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;

30
drivers/md/raid5.h
View File

@ -487,35 +487,6 @@ 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
@ -613,6 +584,7 @@ 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;