Date: Fri, 23 Dec 2022 16:27:53 +0100 From: Mateusz Guzik <mjguzik@gmail.com> To: "Alexander V. Chernikov" <melifaro@ipfw.ru> Cc: Zhenlei Huang <zlei.huang@gmail.com>, freebsd-jail@freebsd.org Subject: Re: Is it possible to employ epoch to simplify managing prison lifecycle Message-ID: <CAGudoHEncQfMXuG1UHrGRbaHchVfp2pC79mZvHNBUDh-XNhDFA@mail.gmail.com> In-Reply-To: <4E70D6D2-4E80-4AAD-BB3C-9295F586D1FF@ipfw.ru> References: <9BD54A54-A809-4D3E-BCBA-639E6C61FE37@FreeBSD.org> <CAGudoHHe8zo%2B7x4Myhotj60BJsASuV109Aj_Rkhg95RNVsTeaw@mail.gmail.com> <4E70D6D2-4E80-4AAD-BB3C-9295F586D1FF@ipfw.ru>
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On 12/23/22, Alexander V. Chernikov <melifaro@ipfw.ru> wrote: > > >> On 16 Dec 2022, at 16:29, Mateusz Guzik <mjguzik@gmail.com> wrote: >> >> On 12/16/22, Zhenlei Huang <zlei.huang@gmail.com> wrote: >>> Hi, >>> >>> While hacking `sys/kern/kern_jail.c` I got lost. >>> >>> There're lots of ref / unref and flags to prevent visit invalid prison >>> while >>> concurrent modification is possible and some refs looks weird. >>> >>> Is it possible to employ epoch(9) to simplify managing of prison >>> lifecycle >>> ? >>> >> >> Some of the ref/unref cycles are probably avoidable to begin with, but >> ultimately the thing to do here is to employ per-cpu reference >> counting, if at all needed. >> >> I have a wip patch to provide such a mechanism, it may or may not land >> this month. > That would be nice. I=E2=80=99d love to convert nextops refcounting to th= at one. > Do you envision similar semantics as Linux percpu_ref? I mean, does one n= eed > to explicitly mark =E2=80=9Cnot in active use=E2=80=9D stage? There *something* needed to disable per-cpu operation, otherwise how can you ever know if the count is 0, apart from going over all cpus every time, which defeats the point. More specifically, I have a on/off switch for said per-cpu op. This is modeled after what I did for counters in vfs, see vfs_ref et al. --=20 Mateusz Guzik <mjguzik gmail.com>
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