make_request() does stripe release for every stripe and the stripe usually has
count 1, which makes previous release_stripe() optimization not work. In my
test, this release_stripe() becomes the heaviest pleace to take
conf->device_lock after previous patches applied.
Below patch makes stripe release batch. All the stripes will be released in
unplug. The STRIPE_ON_UNPLUG_LIST bit is to protect concurrent access stripe
lru.
Signed-off-by: Shaohua Li <shli@xxxxxxxxxxxx>
---
drivers/md/raid5.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++-----
drivers/md/raid5.h | 1
2 files changed, 60 insertions(+), 5 deletions(-)
Index: linux/drivers/md/raid5.c
===================================================================
--- linux.orig/drivers/md/raid5.c 2012-06-25 14:38:33.110889008 +0800
+++ linux/drivers/md/raid5.c 2012-06-25 14:38:37.378835415 +0800
@@ -484,7 +484,8 @@ get_active_stripe(struct r5conf *conf, s
} else {
if (atomic_read(&sh->count)) {
BUG_ON(!list_empty(&sh->lru)
- && !test_bit(STRIPE_EXPANDING, &sh->state));
+ && !test_bit(STRIPE_EXPANDING, &sh->state)
+ && !test_bit(STRIPE_ON_UNPLUG_LIST, &sh->state));
} else {
if (!test_bit(STRIPE_HANDLE, &sh->state))
atomic_inc(&conf->active_stripes);
@@ -3984,6 +3985,51 @@ static struct stripe_head *__get_priorit
return sh;
}
+#define raid5_unplug_list(mdcb) (struct list_head *)(mdcb + 1)
+static void raid5_unplug(struct md_plug_cb *mdcb)
+{
+ struct list_head *list = raid5_unplug_list(mdcb);
+ struct stripe_head *sh;
+ struct r5conf *conf = mdcb->mddev->private;
+
+ if (list->next == NULL || list_empty(list))
+ return;
+ spin_lock_irq(&conf->device_lock);
+ while (!list_empty(list)) {
+ sh = list_entry(list->next, struct stripe_head, lru);
+ list_del_init(&sh->lru);
+ /*
+ * avoid race release_stripe_plug() sees STRIPE_ON_UNPLUG_LIST
+ * clear but the stripe is still in our list
+ */
+ smp_mb__before_clear_bit();
+ clear_bit(STRIPE_ON_UNPLUG_LIST, &sh->state);
+ __release_stripe(conf, sh);
+ }
+ spin_unlock_irq(&conf->device_lock);
+}
+
+static void release_stripe_plug(struct md_plug_cb *mdcb,
+ struct stripe_head *sh)
+{
+ struct list_head *list = raid5_unplug_list(mdcb);
+
+ if (!mdcb) {
+ release_stripe(sh);
+ return;
+ }
+
+ if (list->next == NULL) {
+ INIT_LIST_HEAD(list);
+ mdcb->unplug = raid5_unplug;
+ }
+
+ if (!test_and_set_bit(STRIPE_ON_UNPLUG_LIST, &sh->state))
+ list_add_tail(&sh->lru, list);
+ else
+ release_stripe(sh);
+}
+
static void make_request(struct mddev *mddev, struct bio * bi)
{
struct r5conf *conf = mddev->private;
@@ -3993,7 +4039,7 @@ static void make_request(struct mddev *m
struct stripe_head *sh;
const int rw = bio_data_dir(bi);
int remaining;
- int plugged;
+ struct md_plug_cb *mdcb;
if (unlikely(bi->bi_rw & REQ_FLUSH)) {
md_flush_request(mddev, bi);
@@ -4012,7 +4058,8 @@ static void make_request(struct mddev *m
bi->bi_next = NULL;
bi->bi_phys_segments = 1; /* over-loaded to count active stripes */
- plugged = !!mddev_check_plugged(mddev, NULL, 0);
+ mdcb = mddev_check_plugged(mddev, raid5_unplug,
+ sizeof(struct list_head));
for (;logical_sector < last_sector; logical_sector += STRIPE_SECTORS) {
DEFINE_WAIT(w);
int previous;
@@ -4114,7 +4161,14 @@ static void make_request(struct mddev *m
if ((bi->bi_rw & REQ_SYNC) &&
!test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
atomic_inc(&conf->preread_active_stripes);
- release_stripe(sh);
+ /*
+ * We must recheck here. schedule() might be called
+ * above which makes unplug invoked already, so the old
+ * mdcb is invalid
+ */
+ mdcb = mddev_check_plugged(mddev, raid5_unplug,
+ sizeof(struct list_head));
+ release_stripe_plug(mdcb, sh);
} else {
/* cannot get stripe for read-ahead, just give-up */
clear_bit(BIO_UPTODATE, &bi->bi_flags);
@@ -4123,7 +4177,7 @@ static void make_request(struct mddev *m
}
}
- if (!plugged)
+ if (!mdcb)
md_wakeup_thread(mddev->thread);
remaining = raid5_dec_bi_active_stripes(bi);
Index: linux/drivers/md/raid5.h
===================================================================
--- linux.orig/drivers/md/raid5.h 2012-06-25 14:37:13.651888057 +0800
+++ linux/drivers/md/raid5.h 2012-06-25 14:38:37.382835318 +0800
@@ -320,6 +320,7 @@ enum {
STRIPE_BIOFILL_RUN,
STRIPE_COMPUTE_RUN,
STRIPE_OPS_REQ_PENDING,
+ STRIPE_ON_UNPLUG_LIST,
};
/*
--
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