linux-kernel - Re: [PATCH v3 08/34] ia64: mm: Add p?d

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Message-ID: <20190304190637.GA13947@agluck-desk>
Date:   Mon, 4 Mar 2019 11:06:37 -0800
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Steven Price <steven.price@....com>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Mark Rutland <Mark.Rutland@....com>,
        linux-ia64@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Will Deacon <will.deacon@....com>, linux-mm@...ck.org,
        "H. Peter Anvin" <hpa@...or.com>,
        "Liang, Kan" <kan.liang@...ux.intel.com>, x86@...nel.org,
        Ingo Molnar <mingo@...hat.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        Jérôme Glisse <jglisse@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-kernel@...r.kernel.org, James Morse <james.morse@....com>
Subject: Re: [PATCH v3 08/34] ia64: mm: Add p?d_large() definitions

On Mon, Mar 04, 2019 at 01:16:47PM +0000, Steven Price wrote:
> On 01/03/2019 21:57, Kirill A. Shutemov wrote:
> > On Wed, Feb 27, 2019 at 05:05:42PM +0000, Steven Price wrote:
> >> walk_page_range() is going to be allowed to walk page tables other than
> >> those of user space. For this it needs to know when it has reached a
> >> 'leaf' entry in the page tables. This information is provided by the
> >> p?d_large() functions/macros.
> >>
> >> For ia64 leaf entries are always at the lowest level, so implement
> >> stubs returning 0.
> > 
> > Are you sure about this? I see pte_mkhuge defined for ia64 and Kconfig
> > contains hugetlb references.
> > 
> 
> I'm not completely familiar with ia64, but my understanding is that it
> doesn't have the situation where a page table walk ends early - there is
> always the full depth of entries. The p?d_huge() functions always return 0.
> 
> However my understanding is that it does support huge TLB entries, so
> when populating the TLB a region larger than a standard page can be mapped.
> 
> I'd definitely welcome review by someone more familiar with ia64 to
> check my assumptions.

ia64 has several ways to manage page tables. The one
used by Linux has multi-level table walks like other
architectures, but we don't allow mixing of different
page sizes within a "region" (there are eight regions
selected by the high 3 bits of the virtual address).

Is the series in some GIT tree that I can pull, rather
than tracking down all 34 pieces?  I can try it out and
see if things work/break.

-Tony