LGTM on first read-- I'll read it again and test in test branch.
Reviewed-by: Michael Lyle <ml...@lyle.org>
On 01/26/2018 12:24 AM, tang.jun...@zte.com.cn wrote:
> From: Tang Junhui <tang.jun...@zte.com.cn>
>
> After long time small writing I/O running, we found the occupancy of CPU
> is very high and I/O performance has been reduced by about half:
>
> [root@ceph151 internal]# top
> top - 15:51:05 up 1 day,2:43, 4 users, load average: 16.89, 15.15, 16.53
> Tasks: 2063 total, 4 running, 2059 sleeping, 0 stopped, 0 zombie
> %Cpu(s):4.3 us, 17.1 sy 0.0 ni, 66.1 id, 12.0 wa, 0.0 hi, 0.5 si, 0.0 st
> KiB Mem : 65450044 total, 24586420 free, 38909008 used, 1954616 buff/cache
> KiB Swap: 65667068 total, 65667068 free, 0 used. 25136812 avail Mem
>
> PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
> 2023 root 20 0 0 0 0 S 55.1 0.0 0:04.42 kworker/11:191
> 14126 root 20 0 0 0 0 S 42.9 0.0 0:08.72 kworker/10:3
> 9292 root 20 0 0 0 0 S 30.4 0.0 1:10.99 kworker/6:1
> 8553 ceph 20 0 4242492 1.805g 18804 S 30.0 2.9 410:07.04 ceph-osd
> 12287 root 20 0 0 0 0 S 26.7 0.0 0:28.13 kworker/7:85
> 31019 root 20 0 0 0 0 S 26.1 0.0 1:30.79 kworker/22:1
> 1787 root 20 0 0 0 0 R 25.7 0.0 5:18.45 kworker/8:7
> 32169 root 20 0 0 0 0 S 14.5 0.0 1:01.92 kworker/23:1
> 21476 root 20 0 0 0 0 S 13.9 0.0 0:05.09 kworker/1:54
> 2204 root 20 0 0 0 0 S 12.5 0.0 1:25.17 kworker/9:10
> 16994 root 20 0 0 0 0 S 12.2 0.0 0:06.27 kworker/5:106
> 15714 root 20 0 0 0 0 R 10.9 0.0 0:01.85 kworker/19:2
> 9661 ceph 20 0 4246876 1.731g 18800 S 10.6 2.8 403:00.80 ceph-osd
> 11460 ceph 20 0 4164692 2.206g 18876 S 10.6 3.5 360:27.19 ceph-osd
> 9960 root 20 0 0 0 0 S 10.2 0.0 0:02.75 kworker/2:139
> 11699 ceph 20 0 4169244 1.920g 18920 S 10.2 3.1 355:23.67 ceph-osd
> 6843 ceph 20 0 4197632 1.810g 18900 S 9.6 2.9 380:08.30 ceph-osd
>
> The kernel work consumed a lot of CPU, and I found they are running journal
> work, The journal is reclaiming source and flush btree node with surprising
> frequency.
>
> Through further analysis, we found that in btree_flush_write(), we try to
> get a btree node with the smallest fifo idex to flush by traverse all the
> btree nodein c->bucket_hash, after we getting it, since no locker protects
> it, this btree node may have been written to cache device by other works,
> and if this occurred, we retry to traverse in c->bucket_hash and get
> another btree node. When the problem occurrd, the retry times is very high,
> and we consume a lot of CPU in looking for a appropriate btree node.
>
> In this patch, we try to record 128 btree nodes with the smallest fifo idex
> in heap, and pop one by one when we need to flush btree node. It greatly
> reduces the time for the loop to find the appropriate BTREE node, and also
> reduce the occupancy of CPU.
>
> Signed-off-by: Tang Junhui <tang.jun...@zte.com.cn>
> ---
> drivers/md/bcache/bcache.h | 2 ++
> drivers/md/bcache/journal.c | 47
> ++++++++++++++++++++++++++++++---------------
> 2 files changed, 34 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
> index 0432e28..b343ba4 100644
> --- a/drivers/md/bcache/bcache.h
> +++ b/drivers/md/bcache/bcache.h
> @@ -669,6 +669,8 @@ struct cache_set {
>
> #define BUCKET_HASH_BITS 12
> struct hlist_head bucket_hash[1 << BUCKET_HASH_BITS];
> +
> + DECLARE_HEAP(struct btree *, flush_btree);
> };
>
> struct bbio {
> diff --git a/drivers/md/bcache/journal.c b/drivers/md/bcache/journal.c
> index 47fd0b8..f42d3ea 100644
> --- a/drivers/md/bcache/journal.c
> +++ b/drivers/md/bcache/journal.c
> @@ -363,6 +363,12 @@ int bch_journal_replay(struct cache_set *s, struct
> list_head *list)
> }
>
> /* Journalling */
> +#define journal_max_cmp(l, r) \
> + (fifo_idx(&c->journal.pin, btree_current_write(l)->journal) < \
> + fifo_idx(&(c)->journal.pin, btree_current_write(r)->journal))
> +#define journal_min_cmp(l, r) \
> + (fifo_idx(&c->journal.pin, btree_current_write(l)->journal) > \
> + fifo_idx(&(c)->journal.pin, btree_current_write(r)->journal))
>
> static void btree_flush_write(struct cache_set *c)
> {
> @@ -370,25 +376,35 @@ static void btree_flush_write(struct cache_set *c)
> * Try to find the btree node with that references the oldest journal
> * entry, best is our current candidate and is locked if non NULL:
> */
> - struct btree *b, *best;
> - unsigned i;
> + struct btree *b;
> + int i;
>
> atomic_long_inc(&c->flush_write);
> +
> retry:
> - best = NULL;
> -
> - for_each_cached_btree(b, c, i)
> - if (btree_current_write(b)->journal) {
> - if (!best)
> - best = b;
> - else if (journal_pin_cmp(c,
> - btree_current_write(best)->journal,
> - btree_current_write(b)->journal)) {
> - best = b;
> + spin_lock(&c->journal.lock);
> + if (heap_empty(&c->flush_btree)) {
> + for_each_cached_btree(b, c, i)
> + if (btree_current_write(b)->journal) {
> + if (!heap_full(&c->flush_btree))
> + heap_add(&c->flush_btree, b,
> + journal_max_cmp);
> + else if (journal_max_cmp(b,
> + heap_peek(&c->flush_btree))) {
> + c->flush_btree.data[0] = b;
> + heap_sift(&c->flush_btree, 0,
> + journal_max_cmp);
> + }
> }
> - }
>
> - b = best;
> + for (i = c->flush_btree.used / 2 - 1; i >= 0; --i)
> + heap_sift(&c->flush_btree, i, journal_min_cmp);
> + }
> +
> + b = NULL;
> + heap_pop(&c->flush_btree, b, journal_min_cmp);
> + spin_unlock(&c->journal.lock);
> +
> if (b) {
> mutex_lock(&b->write_lock);
> if (!btree_current_write(b)->journal) {
> @@ -819,7 +835,8 @@ int bch_journal_alloc(struct cache_set *c)
> j->w[0].c = c;
> j->w[1].c = c;
>
> - if (!(init_fifo(&j->pin, JOURNAL_PIN, GFP_KERNEL)) ||
> + if (!(init_heap(&c->flush_btree, 128, GFP_KERNEL)) ||
> + !(init_fifo(&j->pin, JOURNAL_PIN, GFP_KERNEL)) ||
> !(j->w[0].data = (void *) __get_free_pages(GFP_KERNEL, JSET_BITS))
> ||
> !(j->w[1].data = (void *) __get_free_pages(GFP_KERNEL, JSET_BITS)))
> return -ENOMEM;
>
