From: Catalin Marinas <catalin.marinas@arm.com>
To: David Hildenbrand <david@redhat.com>
Cc: Jianyong Wu <Jianyong.Wu@arm.com>,
Anshuman Khandual <Anshuman.Khandual@arm.com>,
"will@kernel.org" <will@kernel.org>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"ardb@kernel.org" <ardb@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"gshan@redhat.com" <gshan@redhat.com>,
Justin He <Justin.He@arm.com>, nd <nd@arm.com>
Subject: Re: [PATCH v2] arm64/mm: avoid fixmap race condition when create pud mapping
Date: Mon, 13 Dec 2021 09:57:08 +0000 [thread overview]
Message-ID: <YbcY9Kjd2ZzDxOZu@arm.com> (raw)
In-Reply-To: <3366ba9f-5993-1c52-de0c-53e618f20cd8@redhat.com>
On Mon, Dec 13, 2021 at 08:37:04AM +0100, David Hildenbrand wrote:
> On 13.12.21 08:27, Jianyong Wu wrote:
> >>> @@ -359,6 +365,7 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end,
> >>> } while (pudp++, addr = next, addr != end);
> >>>
> >>> pud_clear_fixmap();
> >>> + spin_unlock(&fixmap_lock);
> >>> }
> >>>
> >>> static void __create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys,
> >>>
> >>
> >> As the race could only happen with memory hotplug being enabled, could
> >> not we wrap this around with CONFIG_MEMORY_HOTPLUG, just to narrow
> >> its scope possibly speed up other non-hotplug cases ?
Assuming you can quantify the speed-up...
> > I think it's better.
>
> We better avoid using ifdef if not really necessary, it just uglifies
> the code. We could add
>
> if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
> ...
>
> But should we really try to micto-optimize this code and make it harder
> to read for the purpose of an unproven performance gain? (if there is no
> contention, we'll most probably not even recognize that we're taking a lock)
I agree, I don't see the point of this optimisation.
--
Catalin
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next prev parent reply other threads:[~2021-12-13 10:17 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-10 9:54 [PATCH v2] arm64/mm: avoid fixmap race condition when create pud mapping Jianyong Wu
2021-12-10 11:22 ` Catalin Marinas
2021-12-13 5:24 ` Jianyong Wu
2021-12-13 6:56 ` Anshuman Khandual
2021-12-13 7:27 ` Jianyong Wu
2021-12-13 7:37 ` David Hildenbrand
2021-12-13 9:57 ` Catalin Marinas [this message]
2021-12-13 10:16 ` Anshuman Khandual
2021-12-13 10:35 ` Ard Biesheuvel
2021-12-13 13:45 ` Will Deacon
2021-12-13 14:01 ` Ard Biesheuvel
2021-12-13 16:42 ` Will Deacon
2021-12-15 14:13 ` Qian Cai
2021-12-15 16:02 ` Catalin Marinas
2021-12-15 16:04 ` David Hildenbrand
2021-12-16 3:00 ` Jianyong Wu
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