Hi Kent,
After some test, we saw log in dmesg like below:
[ 1505.282400] bcache: bch_allocator_thread() bcache: invalidating
buckets: free_inc 0/127
[ 1505.285843] bcache: bch_allocator_thread() bcache: not writing prios:
free_inc 0/127
[ 1508.005957] bcache: bch_allocator_thread() bcache: invalidating
buckets: free_inc 0/127
[ 1508.009357] bcache: bch_allocator_thread() bcache: not writing prios:
free_inc 0/127
[ 1512.493609] bcache: bch_allocator_thread() bcache: invalidating
buckets: free_inc 0/127
[ 1512.497070] bcache: bch_allocator_thread() bcache: not writing prios:
free_inc 0/127
Does this show some clue to you?
Regards,
Jack
On 04/22/2013 11:51 PM, Kent Overstreet wrote:
> On Mon, Apr 22, 2013 at 10:27:03PM +0200, Jack Wang wrote:
>> Thanks for reply, Kent, two of my colleagues saw this behaviour, so I
>> think we can reproduce this.
>> If you could give me more detailed guide to narrow it down, I can try it
>> on my side.
>
> So, my current hypothesis is that the problem is the allocator spinning,
> and the IO is from it continually rewriting prios/gens.
>
> But I'm still not sure what's causing the allocator to spin, that's what
> the last patch was supposed to fix.
>
> Can you see if you can reproduce it with this patch, and then tell me
> what shows up in the dmesg log? I expect you'll get a _lot_ of output -
> flip timestamps on in your kernel config, if they're not already on.
> Thanks!
>
> commit 60a09d37d301f88dd0f0f413408821a067966d1a
> Author: Kent Overstreet <koverstreet@xxxxxxxxxx>
> Date: Mon Apr 22 14:49:33 2013 -0700
>
> bcache: Allocator debug patch
>
> diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c
> index 2879487..37c22c6 100644
> --- a/drivers/md/bcache/alloc.c
> +++ b/drivers/md/bcache/alloc.c
> @@ -393,12 +393,15 @@ void bch_allocator_thread(struct closure *cl)
> allocator_wait(ca, !list_empty(&ca->discards));
> do_discard(ca, bucket);
> } else {
> - fifo_push(&ca->free, bucket);
> + BUG_ON(!fifo_push(&ca->free, bucket));
> closure_wake_up(&ca->set->bucket_wait);
> }
> }
>
> allocator_wait(ca, ca->set->gc_mark_valid);
> +
> + printk(KERN_DEBUG "bcache: invalidating buckets: free_inc %zu/%zu\n",
> + fifo_used(&ca->free_inc), ca->free_inc.size);
> invalidate_buckets(ca);
>
> allocator_wait(ca, !atomic_read(&ca->set->prio_blocked) ||
> @@ -407,8 +410,12 @@ void bch_allocator_thread(struct closure *cl)
> if (CACHE_SYNC(&ca->set->sb) &&
> (!fifo_empty(&ca->free_inc) ||
> ca->need_save_prio > 64)) {
> + printk(KERN_DEBUG "bcache: writing prios: free_inc %zu/%zu\n",
> + fifo_used(&ca->free_inc), ca->free_inc.size);
> bch_prio_write(ca);
> - }
> + } else
> + printk(KERN_DEBUG "bcache: not writing prios: free_inc %zu/%zu\n",
> + fifo_used(&ca->free_inc), ca->free_inc.size);
> }
> }
>
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