Messages in this thread | | | Date | Mon, 13 Dec 2021 09:57:08 +0000 | From | Catalin Marinas <> | Subject | Re: [PATCH v2] arm64/mm: avoid fixmap race condition when create pud mapping |
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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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