Re: [PATCH 1/5] sbitmap: don't consume nr for inactive waitqueue to avoid lost wakeups

[Gabriel Krisman Bertazi]

Kemeng Shi <shikemeng@xxxxxxxxxx> writes:

> If we decremented queue without waiters, we should not decremente freed
> bits number "nr", or all "nr" could be consumed in a empty queue and no
> wakeup will be called.
> Currently, for case "wait_cnt > 0", "nr" will not be decremented if we
> decremented queue without watiers and retry is returned to avoid lost
> wakeups. However for case "wait_cnt == 0", "nr" will be decremented
> unconditionally and maybe decremented to zero. Although retry is
> returned by active state of queue, it's not actually executed for "nr"
> is zero.
>

Hi Kemeng,

Fwiw, I sent a patch rewriting this algorithm which is now merged in
axboe/for-next.  It drops the per-waitqueue wait_cnt entirely.  You can
find it here:

https://lore.kernel.org/lkml/20221110153533.go5qs3psm75h27mx@quack3/T/

Thanks!


-- 
Gabriel Krisman Bertazi