This is a second version of the patche - it changes the condition in
writecache_pop_from_freelist, to avoid wakeup storm if wc->writeback_size
is greater than wc->freelist_low_watermark-wc->freelist_high_watermark.
From: Mikulas Patocka <mpato...@redhat.com>
Fix a bug that low watermark was ignored and high watermark was used as
both low and high.
The patch also verifies that high watermark is greater or equal than low
watermark - if this condition is violated, the driver would consume too
much CPU.
Signed-off-by: Mikulas Patocka <mpato...@redhat.com>
---
drivers/md/dm-writecache.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
Index: linux-2.6/drivers/md/dm-writecache.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-writecache.c 2018-06-07 22:37:48.000000000
+0200
+++ linux-2.6/drivers/md/dm-writecache.c 2018-06-07 22:38:18.000000000
+0200
@@ -644,7 +644,7 @@ static struct wc_entry *writecache_pop_f
list_del(&e->lru);
}
wc->freelist_size--;
- if (unlikely(wc->freelist_size <= wc->freelist_high_watermark))
+ if (unlikely(wc->freelist_size + wc->writeback_size <=
wc->freelist_high_watermark))
queue_work(wc->writeback_wq, &wc->writeback_work);
return e;
@@ -1590,7 +1590,7 @@ restart:
wbl.size = 0;
while (!list_empty(&wc->lru) &&
(wc->writeback_all ||
- wc->freelist_size + wc->writeback_size <=
wc->freelist_high_watermark)) {
+ wc->freelist_size + wc->writeback_size <=
wc->freelist_low_watermark)) {
n_walked++;
if (unlikely(n_walked > WRITEBACK_LATENCY) &&
@@ -2033,6 +2033,12 @@ invalid_optional:
}
}
+ if (high_wm_percent < low_wm_percent) {
+ r = -EINVAL;
+ ti->error = "High watermark must be greater or equal than low
watermark";
+ goto bad;
+ }
+
if (!WC_MODE_PMEM(wc)) {
struct dm_io_region region;
struct dm_io_request req;
--
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