Re: [PATCH] perf lock contention: Do not use BPF task local storage
From: Martin KaFai Lau
Date: Tue Jan 10 2023 - 01:29:23 EST
On 1/9/23 7:29 PM, Hou Tao wrote:
Hi Martin,
On 1/10/2023 5:22 AM, Martin KaFai Lau wrote:
On 1/9/23 12:56 PM, Namhyung Kim wrote:
Hello,
On Mon, Nov 21, 2022 at 9:33 AM Martin KaFai Lau <martin.lau@xxxxxxxxx> wrote:
On 11/18/22 11:01 AM, Namhyung Kim wrote:
We could fix the task local storage to use the safe BPF allocator,
but it takes time so let's change this until it happens actually.
I also got another report on the kfree_rcu path. I am also looking into this
direction on using the BPF allocator.
Any progress on this? Are there any concerns about the change?
Yep, I am working on it. It is not a direct replacement from kzalloc to
bpf_mem_cache_alloc. eg. Some changes in the bpf mem allocator is needed to
ensure the free list cannot be reused before the rcu grace period. There is a
similar RFC patchset going into this direction that I am trying with.
.
Do you mean "[RFC PATCH bpf-next 0/6] bpf: Handle reuse in bpf memory alloc"
[0], right ?
Yes, that is the RFC patch I was referring :). I was planning to comment after
looking at the patch in details. I have shared some of my quick thoughts in that
thread for the local storage usages.
The main concern [1] for the proposal is the possibility of OOM
will increase when RCU tasks trace grace period is slow, because the immediate
reuse is disabled and the reuse is only possible after one RCU tasks trace grace
period. Using a memory cgroup and setting a hard-limit on the cgroup may reduce
the influence of the OOM problem, but it is not good enough. So do you have
other ways to mitigate the potential OOM problem ?
[0]: https://lore.kernel.org/bpf/20221230041151.1231169-1-houtao@xxxxxxxxxxxxxxx/
[1]:
https://lore.kernel.org/bpf/CAADnVQ+z-Y6Yv2i-icAUy=Uyh9yiN4S1AOrLd=K8mu32TXORkw@xxxxxxxxxxxxxx/