linux-kernel - Re: [PATCH] mm/pgtable: Drop pgtable_t variable from pte_fn

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Message-ID: <20190503132733.GA5201@bombadil.infradead.org>
Date:   Fri, 3 May 2019 06:27:33 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Martin Schwidefsky <schwidefsky@...ibm.com>
Cc:     Anshuman Khandual <anshuman.khandual@....com>,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Michal Hocko <mhocko@...e.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>, jglisse@...hat.com,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>, x86@...nel.org,
        linux-efi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] mm/pgtable: Drop pgtable_t variable from pte_fn_t
 functions

On Thu, May 02, 2019 at 04:14:57PM +0200, Martin Schwidefsky wrote:
> On Thu, 2 May 2019 06:46:23 -0700
> Matthew Wilcox <willy@...radead.org> wrote:
> 
> > On Thu, May 02, 2019 at 06:48:46PM +0530, Anshuman Khandual wrote:
> > > Drop the pgtable_t variable from all implementation for pte_fn_t as none of
> > > them use it. apply_to_pte_range() should stop computing it as well. Should
> > > help us save some cycles.  
> > 
> > You didn't add Martin Schwidefsky for some reason.  He introduced
> > it originally for s390 for sub-page page tables back in 2008 (commit
> > 2f569afd9c).  I think he should confirm that he no longer needs it.
> 
> With its 2K pte tables s390 can not deal with a (struct page *) as a reference
> to a page table. But if there are no user of the apply_to_page_range() API
> left which actually make use of the token argument we can safely drop it.

Interestingly, I don't think there ever was a user which used that
argument.  Looking at your 2f56 patch, you only converted one function
(presumably there was only one caller of apply_to_page_range() at the
time), and it didn't u se any of the arguments.  Xen was the initial user,
and the two other functions they added also didn't use that argument.

Looking at a quick sample of users added since, none of them appear to
have ever used that argument.  So removing it seems best.

Acked-by: Matthew Wilcox <willy@...radead.org>