* [PATCH v2 0/3] btrfs async discard fixes & improvements
@ 2020-12-02 19:39 Pavel Begunkov
2020-12-02 19:39 ` [PATCH v2 1/3] btrfs: fix async discard stall Pavel Begunkov
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: Pavel Begunkov @ 2020-12-02 19:39 UTC (permalink / raw)
To: Chris Mason, Josef Bacik, David Sterba, linux-btrfs
v2: fix async discard stalls [1/3]
Two others are same but rebased on top. [2/3] fixes not important
stats torn reads, [3/3] saves a bit of locking.
note: based on for-next
Pavel Begunkov (3):
btrfs: fix async discard stall
btrfs: fix racy access to discard_ctl data
btrfs: don't overabuse discard lock
fs/btrfs/discard.c | 66 +++++++++++++++++++++++-----------------------
1 file changed, 33 insertions(+), 33 deletions(-)
--
2.24.0
^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH v2 1/3] btrfs: fix async discard stall
2020-12-02 19:39 [PATCH v2 0/3] btrfs async discard fixes & improvements Pavel Begunkov
@ 2020-12-02 19:39 ` Pavel Begunkov
2020-12-02 19:39 ` [PATCH v2 2/3] btrfs: fix racy access to discard_ctl data Pavel Begunkov
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: Pavel Begunkov @ 2020-12-02 19:39 UTC (permalink / raw)
To: Chris Mason, Josef Bacik, David Sterba, linux-btrfs
It might happen that bg->discard_eligible_time was changed without
rescheduling, so btrfs_discard_workfn() would be awaken before that
eligible time, peek_discard_list() returns null, and all discarding
going to sleep until somewhat else calls for rescheduling again.
Fix the stall by keeping btrfs_discard_workfn() going by always calling
btrfs_discard_schedule_work() when there is any block group in the
discard lists.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
fs/btrfs/discard.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/fs/btrfs/discard.c b/fs/btrfs/discard.c
index 1db966bf85b2..4ca852445873 100644
--- a/fs/btrfs/discard.c
+++ b/fs/btrfs/discard.c
@@ -199,10 +199,9 @@ static struct btrfs_block_group *find_next_block_group(
static struct btrfs_block_group *peek_discard_list(
struct btrfs_discard_ctl *discard_ctl,
enum btrfs_discard_state *discard_state,
- int *discard_index)
+ int *discard_index, u64 now)
{
struct btrfs_block_group *block_group;
- const u64 now = ktime_get_ns();
spin_lock(&discard_ctl->lock);
again:
@@ -224,10 +223,7 @@ static struct btrfs_block_group *peek_discard_list(
discard_ctl->block_group = block_group;
*discard_state = block_group->discard_state;
*discard_index = block_group->discard_index;
- } else {
- block_group = NULL;
}
-
spin_unlock(&discard_ctl->lock);
return block_group;
@@ -438,13 +434,18 @@ static void btrfs_discard_workfn(struct work_struct *work)
int discard_index = 0;
u64 trimmed = 0;
u64 minlen = 0;
+ u64 now = ktime_get_ns();
discard_ctl = container_of(work, struct btrfs_discard_ctl, work.work);
block_group = peek_discard_list(discard_ctl, &discard_state,
- &discard_index);
+ &discard_index, now);
if (!block_group || !btrfs_run_discard_work(discard_ctl))
return;
+ if (now < block_group->discard_eligible_time) {
+ btrfs_discard_schedule_work(discard_ctl, false);
+ return;
+ }
/* Perform discarding */
minlen = discard_minlen[discard_index];
--
2.24.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH v2 2/3] btrfs: fix racy access to discard_ctl data
2020-12-02 19:39 [PATCH v2 0/3] btrfs async discard fixes & improvements Pavel Begunkov
2020-12-02 19:39 ` [PATCH v2 1/3] btrfs: fix async discard stall Pavel Begunkov
@ 2020-12-02 19:39 ` Pavel Begunkov
2020-12-02 19:39 ` [PATCH v2 3/3] btrfs: don't overabuse discard lock Pavel Begunkov
2020-12-02 21:51 ` [PATCH v2 0/3] btrfs async discard fixes & improvements Josef Bacik
3 siblings, 0 replies; 5+ messages in thread
From: Pavel Begunkov @ 2020-12-02 19:39 UTC (permalink / raw)
To: Chris Mason, Josef Bacik, David Sterba, linux-btrfs
Because only one discard worker may be running at any given point, it
could have been safe to modify ->prev_discard, etc. without
synchronisation, if not for @override flag in
btrfs_discard_schedule_work() and delayed_work_pending() returning false
while workfn is running.
That may lead lead to torn reads of u64 for some architectures, but
that's not a big problem as only slightly affects the discard rate.
Suggested-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
fs/btrfs/discard.c | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)
diff --git a/fs/btrfs/discard.c b/fs/btrfs/discard.c
index 4ca852445873..a338f44fec3b 100644
--- a/fs/btrfs/discard.c
+++ b/fs/btrfs/discard.c
@@ -475,13 +475,6 @@ static void btrfs_discard_workfn(struct work_struct *work)
discard_ctl->discard_extent_bytes += trimmed;
}
- /*
- * Updated without locks as this is inside the workfn and nothing else
- * is reading the values
- */
- discard_ctl->prev_discard = trimmed;
- discard_ctl->prev_discard_time = ktime_get_ns();
-
/* Determine next steps for a block_group */
if (block_group->discard_cursor >= btrfs_block_group_end(block_group)) {
if (discard_state == BTRFS_DISCARD_BITMAPS) {
@@ -497,7 +490,10 @@ static void btrfs_discard_workfn(struct work_struct *work)
}
}
+ now = ktime_get_ns();
spin_lock(&discard_ctl->lock);
+ discard_ctl->prev_discard = trimmed;
+ discard_ctl->prev_discard_time = now;
discard_ctl->block_group = NULL;
spin_unlock(&discard_ctl->lock);
--
2.24.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH v2 3/3] btrfs: don't overabuse discard lock
2020-12-02 19:39 [PATCH v2 0/3] btrfs async discard fixes & improvements Pavel Begunkov
2020-12-02 19:39 ` [PATCH v2 1/3] btrfs: fix async discard stall Pavel Begunkov
2020-12-02 19:39 ` [PATCH v2 2/3] btrfs: fix racy access to discard_ctl data Pavel Begunkov
@ 2020-12-02 19:39 ` Pavel Begunkov
2020-12-02 21:51 ` [PATCH v2 0/3] btrfs async discard fixes & improvements Josef Bacik
3 siblings, 0 replies; 5+ messages in thread
From: Pavel Begunkov @ 2020-12-02 19:39 UTC (permalink / raw)
To: Chris Mason, Josef Bacik, David Sterba, linux-btrfs
btrfs_discard_workfn() drops discard_ctl->lock just to take it again in
a moment in btrfs_discard_schedule_work(). Avoid that and also reuse
ktime.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
fs/btrfs/discard.c | 43 +++++++++++++++++++++++--------------------
1 file changed, 23 insertions(+), 20 deletions(-)
diff --git a/fs/btrfs/discard.c b/fs/btrfs/discard.c
index a338f44fec3b..cd3b23f7ceb2 100644
--- a/fs/btrfs/discard.c
+++ b/fs/btrfs/discard.c
@@ -326,28 +326,15 @@ void btrfs_discard_queue_work(struct btrfs_discard_ctl *discard_ctl,
btrfs_discard_schedule_work(discard_ctl, false);
}
-/**
- * btrfs_discard_schedule_work - responsible for scheduling the discard work
- * @discard_ctl: discard control
- * @override: override the current timer
- *
- * Discards are issued by a delayed workqueue item. @override is used to
- * update the current delay as the baseline delay interval is reevaluated on
- * transaction commit. This is also maxed with any other rate limit.
- */
-void btrfs_discard_schedule_work(struct btrfs_discard_ctl *discard_ctl,
- bool override)
+static void __btrfs_discard_schedule_work(struct btrfs_discard_ctl *discard_ctl,
+ u64 now, bool override)
{
struct btrfs_block_group *block_group;
- const u64 now = ktime_get_ns();
-
- spin_lock(&discard_ctl->lock);
if (!btrfs_run_discard_work(discard_ctl))
- goto out;
-
+ return;
if (!override && delayed_work_pending(&discard_ctl->work))
- goto out;
+ return;
block_group = find_next_block_group(discard_ctl, now);
if (block_group) {
@@ -389,7 +376,24 @@ void btrfs_discard_schedule_work(struct btrfs_discard_ctl *discard_ctl,
mod_delayed_work(discard_ctl->discard_workers,
&discard_ctl->work, nsecs_to_jiffies(delay));
}
-out:
+}
+
+/**
+ * btrfs_discard_schedule_work - responsible for scheduling the discard work
+ * @discard_ctl: discard control
+ * @override: override the current timer
+ *
+ * Discards are issued by a delayed workqueue item. @override is used to
+ * update the current delay as the baseline delay interval is reevaluated on
+ * transaction commit. This is also maxed with any other rate limit.
+ */
+void btrfs_discard_schedule_work(struct btrfs_discard_ctl *discard_ctl,
+ bool override)
+{
+ u64 now = ktime_get_ns();
+
+ spin_lock(&discard_ctl->lock);
+ __btrfs_discard_schedule_work(discard_ctl, now, override);
spin_unlock(&discard_ctl->lock);
}
@@ -495,9 +499,8 @@ static void btrfs_discard_workfn(struct work_struct *work)
discard_ctl->prev_discard = trimmed;
discard_ctl->prev_discard_time = now;
discard_ctl->block_group = NULL;
+ __btrfs_discard_schedule_work(discard_ctl, now, false);
spin_unlock(&discard_ctl->lock);
-
- btrfs_discard_schedule_work(discard_ctl, false);
}
/**
--
2.24.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v2 0/3] btrfs async discard fixes & improvements
2020-12-02 19:39 [PATCH v2 0/3] btrfs async discard fixes & improvements Pavel Begunkov
` (2 preceding siblings ...)
2020-12-02 19:39 ` [PATCH v2 3/3] btrfs: don't overabuse discard lock Pavel Begunkov
@ 2020-12-02 21:51 ` Josef Bacik
3 siblings, 0 replies; 5+ messages in thread
From: Josef Bacik @ 2020-12-02 21:51 UTC (permalink / raw)
To: Pavel Begunkov, Chris Mason, David Sterba, linux-btrfs
On 12/2/20 2:39 PM, Pavel Begunkov wrote:
> v2: fix async discard stalls [1/3]
>
> Two others are same but rebased on top. [2/3] fixes not important
> stats torn reads, [3/3] saves a bit of locking.
>
> note: based on for-next
>
> Pavel Begunkov (3):
> btrfs: fix async discard stall
> btrfs: fix racy access to discard_ctl data
> btrfs: don't overabuse discard lock
>
> fs/btrfs/discard.c | 66 +++++++++++++++++++++++-----------------------
> 1 file changed, 33 insertions(+), 33 deletions(-)
>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Thanks,
Josef
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2020-12-02 21:52 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2020-12-02 19:39 [PATCH v2 0/3] btrfs async discard fixes & improvements Pavel Begunkov
2020-12-02 19:39 ` [PATCH v2 1/3] btrfs: fix async discard stall Pavel Begunkov
2020-12-02 19:39 ` [PATCH v2 2/3] btrfs: fix racy access to discard_ctl data Pavel Begunkov
2020-12-02 19:39 ` [PATCH v2 3/3] btrfs: don't overabuse discard lock Pavel Begunkov
2020-12-02 21:51 ` [PATCH v2 0/3] btrfs async discard fixes & improvements Josef Bacik
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