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charset="UTF-8" X-Rspamd-Queue-Id: 478631C0020 X-Stat-Signature: emg4xa6mth7to73a7g58nykzqr5yhj9m X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1674233134-576405 X-HE-Meta: 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 PX8kskcC TR66rGGi4kNk/KEOS6Cb0JOCw5gVym+IFGTvhc8gIEBkelE/pvNhyb7zTWwxhiydTtw34RhhiazzgFtmJbKD6NvpGb1B8sdiFM/0eSnwYiCFEpLFVlBLjaeqIedSHu0WWp6JcNWNElsqdeq7Z4VVYsmguzA86X2KJQcPW4cJnAa72faYWfgWadtKsqmYyyjxAlLSKdRuPCjEfs3Fl8bNXGa9dUu7bXJv+GYu8mD/t5sG2aN6w9C0Zmi5ugXPyvgkCbd+0DQwMSiVwlbTL3wpCXI7IOCUI837IM7VH4Yv/8dFkHqnYF4YmVRwvqg1w1RN1Z63Fv0VY7WNt+fdvibju62h8ppE564++xiUkc3nlvXjQwi3oUUdp9ZPAAA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Jan 20, 2023 at 8:20 AM Suren Baghdasaryan wrote: > > On Fri, Jan 20, 2023 at 12:52 AM Michal Hocko wrote: > > > > On Thu 19-01-23 10:52:03, Suren Baghdasaryan wrote: > > > On Thu, Jan 19, 2023 at 4:59 AM Michal Hocko wrote: > > > > > > > > On Mon 09-01-23 12:53:34, Suren Baghdasaryan wrote: > > > > > call_rcu() can take a long time when callback offloading is enabled. > > > > > Its use in the vm_area_free can cause regressions in the exit path when > > > > > multiple VMAs are being freed. To minimize that impact, place VMAs into > > > > > a list and free them in groups using one call_rcu() call per group. > > > > > > > > After some more clarification I can understand how call_rcu might not be > > > > super happy about thousands of callbacks to be invoked and I do agree > > > > that this is not really optimal. > > > > > > > > On the other hand I do not like this solution much either. > > > > VM_AREA_FREE_LIST_MAX is arbitrary and it won't really help all that > > > > much with processes with a huge number of vmas either. It would still be > > > > in housands of callbacks to be scheduled without a good reason. > > > > > > > > Instead, are there any other cases than remove_vma that need this > > > > batching? We could easily just link all the vmas into linked list and > > > > use a single call_rcu instead, no? This would both simplify the > > > > implementation, remove the scaling issue as well and we do not have to > > > > argue whether VM_AREA_FREE_LIST_MAX should be epsilon or epsilon + 1. > > > > > > Yes, I agree the solution is not stellar. I wanted something simple > > > but this is probably too simple. OTOH keeping all dead vm_area_structs > > > on the list without hooking up a shrinker (additional complexity) does > > > not sound too appealing either. > > > > I suspect you have missed my idea. I do not really want to keep the list > > around or any shrinker. It is dead simple. Collect all vmas in > > remove_vma and then call_rcu the whole list at once after the whole list > > (be it from exit_mmap or remove_mt). See? > > Yes, I understood your idea but keeping dead objects until the process > exits even when the system is low on memory (no shrinkers attached) > seems too wasteful. If we do this I would advocate for attaching a > shrinker. Maybe even simpler, since we are hit with this VMA freeing flood during exit_mmap (when all VMAs are destroyed), we pass a hint to vm_area_free to batch the destruction and all other cases call call_rcu()? I don't think there will be other cases of VMA destruction floods. > > > > > -- > > Michal Hocko > > SUSE Labs