linux-kernel - Re: [PATCH v3 00/21] huge page clearing optimizations

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Message-ID: <YqD9ZRNtU1F6zBn/@casper.infradead.org>
Date:   Wed, 8 Jun 2022 20:49:57 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Ankur Arora <ankur.a.arora@...cle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andi Kleen <ak@...ux.intel.com>, Arnd Bergmann <arnd@...db.de>,
        Jason Gunthorpe <jgg@...dia.com>, jon.grimm@....com,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Joao Martins <joao.m.martins@...cle.com>
Subject: Re: [PATCH v3 00/21] huge page clearing optimizations

On Tue, Jun 07, 2022 at 10:56:01AM -0700, Linus Torvalds wrote:
> I worry a bit about the insanity of the "gigantic" pages, and the
> mem_map_next() games it plays, but that code is from 2008 and I really
> doubt it makes any sense to keep around at least for x86. The source
> of that abomination is powerpc, and I do not think that whole issue
> with MAX_ORDER_NR_PAGES makes any difference on x86, at least.

Oh, argh, I meant to delete mem_map_next(), and forgot.

If you need to use struct page (a later message hints you don't), just
use nth_page() directly.  I optimised it so it's not painful except on
SPARSEMEM && !SPARSEMEM_VMEMMAP back in December in commit 659508f9c936.
And nobody cares about performance on SPARSEMEM && !SPARSEMEM_VMEMMAP
systems.