Date: Thu, 11 Mar 2021 20:20:05 +0100 From: Hans Petter Selasky <hps@selasky.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: John Baldwin <jhb@freebsd.org>, src-committers@freebsd.org, dev-commits-src-all@freebsd.org, dev-commits-src-main@freebsd.org Subject: Re: git: d1cbe7908986 - main - Allocating the LinuxKPI current structure from an interrupt thread must be done using the M_NOWAIT flag after 1ae20f7c70ea . Message-ID: <8fe37b5e-29a7-ffeb-fddb-3b31a6e79ab0@selasky.org> In-Reply-To: <YEppt/dtNwdmxDHP@kib.kiev.ua> References: <202103100952.12A9qRKR040117@gitrepo.freebsd.org> <YEiZwWT28AeXzQjA@kib.kiev.ua> <2b1739ab-000c-ca28-5a59-0a3e19ef4591@selasky.org> <5aaa5f2a-a67d-a495-7f56-a6b31c2494c7@FreeBSD.org> <ba608afb-d8bb-242a-9170-e30b2291411e@selasky.org> <YEpi65EJZrFHf5Dj@kib.kiev.ua> <3dcd63b0-fe90-2855-f349-2117ca4b6b26@selasky.org> <YEppt/dtNwdmxDHP@kib.kiev.ua>
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On 3/11/21 8:04 PM, Konstantin Belousov wrote: > On Thu, Mar 11, 2021 at 07:41:53PM +0100, Hans Petter Selasky wrote: >> On 3/11/21 7:35 PM, Konstantin Belousov wrote: >>> And I dislike this. It is yet another case of introducing consumer-specific >>> logic into core. Isn't netepoch example enough? >>> >>> I presented another patch to Hans, where task and mm allocations are >>> switched to zones, and the zones have reserve applied. Then allocations >>> from ithreads use the reserve. >>> >>> There is one detail there, reserve is finite, for x86 I set it to the >>> total limit of interrupts. This somewhat breaks if interrupts are >>> deallocated and reallocated, but I think it is good enough even with >>> this wart. >> >> Hi, >> >> Your patch doesn't address the issue of initializing the pointers in >> question once. Still, for every call, we need to check if the pointer is >> valid. This is not neccessary. > I do not understand what you are saying there. > Which pointers? How does it not address? Hi, The current code calls linux_set_current() for every interrupt and timer callback. That means we continue to check td_lkpi_task for NULL for every one of these calls. Not strictly needed. > >> >> Also I don't see why we need to create a own UMA zone for these simple >> structures. Won't the per-CPU sysctl consume more memory than the actual >> task structures being allocated? > Dedicated UMA zone allows to gracefully solve the requirement of non-failing > allocation in non-sleepable context. This is much simpler and cleaner than > either trying to enumerate all existing ithreads or adding consumer-specific > controls into generic kernel facility. > Maybe I'm new to UMA zones. The M_USE_RESERVE can also be used with malloc() ? --HPS
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