Messages in this thread | | | Date | Thu, 15 Feb 2024 14:45:18 +0100 | Subject | Re: [PATCH net-next] page_pool: disable direct recycling based on pool->cpuid on destroy | From | Alexander Lobakin <> |
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From: Lorenzo Bianconi <lorenzo@kernel.org> Date: Thu, 15 Feb 2024 14:37:10 +0100
>> From: Toke Høiland-Jørgensen <toke@redhat.com> >> Date: Thu, 15 Feb 2024 13:05:30 +0100 >> >>> Alexander Lobakin <aleksander.lobakin@intel.com> writes: >>> >>>> Now that direct recycling is performed basing on pool->cpuid when set, >>>> memory leaks are possible: >>>> >>>> 1. A pool is destroyed. >>>> 2. Alloc cache is emptied (it's done only once). >>>> 3. pool->cpuid is still set. >>>> 4. napi_pp_put_page() does direct recycling basing on pool->cpuid. >>>> 5. Now alloc cache is not empty, but it won't ever be freed. >>> >>> Did you actually manage to trigger this? pool->cpuid is only set for the >>> system page pool instance which is never destroyed; so this seems a very >>> theoretical concern? >> >> To both Lorenzo and Toke: >> >> Yes, system page pools are never destroyed, but we might latter use >> cpuid in non-persistent PPs. Then there will be memory leaks. >> I was able to trigger this by creating bpf/test_run page_pools with the >> cpuid set to test direct recycling of live frames. > > what about avoiding the page to be destroyed int this case? I do not like the
I think I didn't get what you wanted to say here :s
Rewriting cpuid doesn't introduce any new checks on hotpath. Destroying the pool is slowpath and we shouldn't hurt hotpath to handle it.
> idea of overwriting the cpuid field for it.
We also overwrite pp->p.napi field a couple lines below. It happens only when destroying the pool, we don't care about the fields at this point.
> > Regards, > Lorenzo > >> >>> >>> I guess we could still do this in case we find other uses for setting >>> the cpuid; I don't think the addition of the READ_ONCE() will have any >>> measurable overhead on the common arches? >> >> READ_ONCE() is cheap, but I thought it's worth mentioning in the >> commitmsg anyway :) >> >>> >>> -Toke
Thanks, Olek
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