md/raid5: prioritize stripes for writeback
In raid5-cache writeback mode, we have two types of stripes to handle.
- stripes which aren't cached yet
- stripes which are cached and flushing out to raid disks
Upperlayer is more sensistive to latency of the first type of stripes
generally. But we only one handle list for all these stripes, where the
two types of stripes are mixed together. When reclaim flushes a lot of
stripes, the first type of stripes could be noticeably delayed. On the
other hand, if the log space is tight, we'd like to handle the second
type of stripes faster and free log space.
This patch destinguishes the two types stripes. They are added into
different handle list. When we try to get a stripe to handl, we prefer
the first type of stripes unless log space is tight.
This should have no impact for !writeback case.
Signed-off-by: Shaohua Li <shli@fb.com>
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index ed5cd70..5a28bd9 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -176,6 +176,13 @@
test_bit(STRIPE_COMPUTE_RUN, &sh->state);
}
+static bool stripe_is_lowprio(struct stripe_head *sh)
+{
+ return (test_bit(STRIPE_R5C_FULL_STRIPE, &sh->state) ||
+ test_bit(STRIPE_R5C_PARTIAL_STRIPE, &sh->state)) &&
+ !test_bit(STRIPE_R5C_CACHING, &sh->state);
+}
+
static void raid5_wakeup_stripe_thread(struct stripe_head *sh)
{
struct r5conf *conf = sh->raid_conf;
@@ -191,7 +198,10 @@
if (list_empty(&sh->lru)) {
struct r5worker_group *group;
group = conf->worker_groups + cpu_to_group(cpu);
- list_add_tail(&sh->lru, &group->handle_list);
+ if (stripe_is_lowprio(sh))
+ list_add_tail(&sh->lru, &group->loprio_list);
+ else
+ list_add_tail(&sh->lru, &group->handle_list);
group->stripes_cnt++;
sh->group = group;
}
@@ -254,7 +264,12 @@
clear_bit(STRIPE_DELAYED, &sh->state);
clear_bit(STRIPE_BIT_DELAY, &sh->state);
if (conf->worker_cnt_per_group == 0) {
- list_add_tail(&sh->lru, &conf->handle_list);
+ if (stripe_is_lowprio(sh))
+ list_add_tail(&sh->lru,
+ &conf->loprio_list);
+ else
+ list_add_tail(&sh->lru,
+ &conf->handle_list);
} else {
raid5_wakeup_stripe_thread(sh);
return;
@@ -5172,19 +5187,27 @@
*/
static struct stripe_head *__get_priority_stripe(struct r5conf *conf, int group)
{
- struct stripe_head *sh = NULL, *tmp;
+ struct stripe_head *sh, *tmp;
struct list_head *handle_list = NULL;
- struct r5worker_group *wg = NULL;
+ struct r5worker_group *wg;
+ bool second_try = !r5c_is_writeback(conf->log);
+ bool try_loprio = test_bit(R5C_LOG_TIGHT, &conf->cache_state);
+again:
+ wg = NULL;
+ sh = NULL;
if (conf->worker_cnt_per_group == 0) {
- handle_list = &conf->handle_list;
+ handle_list = try_loprio ? &conf->loprio_list :
+ &conf->handle_list;
} else if (group != ANY_GROUP) {
- handle_list = &conf->worker_groups[group].handle_list;
+ handle_list = try_loprio ? &conf->worker_groups[group].loprio_list :
+ &conf->worker_groups[group].handle_list;
wg = &conf->worker_groups[group];
} else {
int i;
for (i = 0; i < conf->group_cnt; i++) {
- handle_list = &conf->worker_groups[i].handle_list;
+ handle_list = try_loprio ? &conf->worker_groups[i].loprio_list :
+ &conf->worker_groups[i].handle_list;
wg = &conf->worker_groups[i];
if (!list_empty(handle_list))
break;
@@ -5235,8 +5258,13 @@
wg = NULL;
}
- if (!sh)
- return NULL;
+ if (!sh) {
+ if (second_try)
+ return NULL;
+ second_try = true;
+ try_loprio = !try_loprio;
+ goto again;
+ }
if (wg) {
wg->stripes_cnt--;
@@ -6546,6 +6574,7 @@
group = &(*worker_groups)[i];
INIT_LIST_HEAD(&group->handle_list);
+ INIT_LIST_HEAD(&group->loprio_list);
group->conf = conf;
group->workers = workers + i * cnt;
@@ -6773,6 +6802,7 @@
init_waitqueue_head(&conf->wait_for_stripe);
init_waitqueue_head(&conf->wait_for_overlap);
INIT_LIST_HEAD(&conf->handle_list);
+ INIT_LIST_HEAD(&conf->loprio_list);
INIT_LIST_HEAD(&conf->hold_list);
INIT_LIST_HEAD(&conf->delayed_list);
INIT_LIST_HEAD(&conf->bitmap_list);