On Sun, Jul 15, 2018 at 12:25 PM, Shakeel Butt <shake...@google.com> wrote: > On Sat, Jul 14, 2018 at 7:10 PM Yafang Shao <laoar.s...@gmail.com> wrote: >> >> On Sat, Jul 14, 2018 at 11:38 PM, Shakeel Butt <shake...@google.com> wrote: >> > On Sat, Jul 14, 2018 at 1:32 AM Yafang Shao <laoar.s...@gmail.com> wrote: >> >> >> >> try_charge maybe executed in packet receive path, which is in interrupt >> >> context. >> >> In this situation, the 'current' is the interrupted task, which may has >> >> no relation to the rx softirq, So it is nonsense to use 'current'. >> >> >> > >> > Have you actually seen this occurring? >> >> Hi Shakeel, >> >> I'm trying to produce this issue, but haven't find it occur yet. >> >> > I am not very familiar with the >> > network code but I can think of two ways try_charge() can be called >> > from network code. Either through kmem charging or through >> > mem_cgroup_charge_skmem() and both locations correctly handle >> > interrupt context. >> > >> >> Why do you say that mem_cgroup_charge_skmem() correctly hanle >> interrupt context ? >> >> Let me show you why mem_cgroup_charge_skmem isn't hanling interrupt >> context correctly. >> >> mem_cgroup_charge_skmem() is calling try_charge() twice. >> The first one is with GFP_NOWAIT as the gfp_mask, and the second one >> is with (GFP_NOWAIT | __GFP_NOFAIL) as the gfp_mask. >> >> If page_counter_try_charge() failes at the first time, -ENOMEM is returned. >> Then mem_cgroup_charge_skmem() will call try_charge() once more with >> __GFP_NOFAIL set, and this time if If page_counter_try_charge() failes >> again the ' >> force' label in try_charge() will be executed and 0 is returned. >> >> No matter what, the 'current' will be used and touched, that is >> meaning mem_cgroup_charge_skmem() isn't hanling the interrupt context >> correctly. >> > > Hi Yafang, > > If you check mem_cgroup_charge_skmem(), the memcg passed is not > 'current' but is from the sock object i.e. sk->sk_memcg for which the > network buffer is allocated for. >
That's correct, the memcg if from the sock object. But the point is, in this situation why 'current' is used in try_charge() ? As 'current' is not related with the memcg, which is just a interrupted task. > If the network buffers is allocated through kmem interface, the > charging is bypassed altogether (through memcg_kmem_bypass()) for > interrupt context. > Yes. Thanks Yafang