Messages in this thread | | | Date | Thu, 31 Jul 2014 21:23:01 -0400 | From | Tejun Heo <> | Subject | Re: [PATCH percpu/for-3.17 1/2] percpu: implement percpu_pool |
| |
Hello, Andrew.
On Thu, Jul 31, 2014 at 06:16:56PM -0700, Andrew Morton wrote: > Yet nowhere in either the changelog or the code comments is it even > mentioned that this allocator is unreliable and that callers *must* > implement (and test!) fallback paths.
Hmmm, yeah, somehow the atomic behavior seemed obvious to me. I'll try to make it clear that this thing can and does fail.
> > an obvious solution is adding a failure > > injection for debugging, but really except for being a bit ghetto, > > this is just the atomic allocation for percpu areas. > > If it was a try-GFP_ATOMIC-then-fall-back-to-pool thing then it would > work fairly well. But it's not even that - a caller could trivially > chew through that pool in a single timeslice. Especially on !SMP. > Especially squared with !PREEMPT or SCHED_FIFO.
Yeap, occassional pool depletion would be a normal thing to happen, which isn't a correctness issue and most likely not even a performance issue.
> But please make very sure that this is how we position it. I don't > know how to do this. Maybe prefix the names with "blk_" to signify > that it is block-private (and won't even be there if !CONFIG_BLOCK). > > Or rename percpu_pool_alloc() to percpu_pool_try_alloc() - that should > wake people up.
Sounds good to me. I'll rename it to percpu_pool_try_alloc() and make it clear in the comment that the allocation is opportunistic.
Thanks.
-- tejun
| |