Tejun Heo <tj@xxxxxxxxxx> writes:
> cfq_find_alloc_queue() checks whether a queue actually needs to be
> allocated, which is unnecessary as its sole caller, cfq_get_queue(),
> only calls it if so. Also, the oom queue fallback logic is scattered
> between cfq_get_queue() and cfq_find_alloc_queue(). There really
> isn't much going on in the latter and things can be made simpler by
> folding it into cfq_get_queue().
>
> This patch collapses cfq_find_alloc_queue() into cfq_get_queue(). The
> change is fairly straight-forward with one exception - async_cfqq is
> now initialized to NULL and the "!is_sync" test in the last if
> conditional is replaced with "async_cfqq" test. This is because gcc
> (5.1.1) gets confused for some reason and warns that async_cfqq may be
> used uninitialized otherwise. Oh well, the code isn't necessarily
> worse this way.
>
> This patch doesn't cause any functional difference.
The resulting code (introduced by the last patch, I know) is not ideal:
rcu_read_lock();
cfqg = cfq_lookup_create_cfqg(cfqd, bio_blkcg(bio));
if (!cfqg) {
cfqq = &cfqd->oom_cfqq;
goto out;
}
if (!is_sync) {
if (!ioprio_valid(cic->ioprio)) {
struct task_struct *tsk = current;
ioprio = task_nice_ioprio(tsk);
ioprio_class = task_nice_ioclass(tsk);
}
async_cfqq = cfq_async_queue_prio(cfqd, ioprio_class,
ioprio);
cfqq = *async_cfqq;
if (cfqq)
goto out;
}
As you mentioned, we don't need to lookup the cfqg for the async queue.
What's more is we could fallback to the oom_cfqq even if we had an
existing async cfqq. I'm guessing you structured the code this way to
make the error path cleaner. I don't think it's a big deal, as it
should be a rare occurrence, so...
Reviewed-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
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