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[217.140.101.70]) by mx.google.com with ESMTP id y18si3471377edc.58.2019.03.22.03.37.19 for ; Fri, 22 Mar 2019 03:37:20 -0700 (PDT) Received-SPF: pass (google.com: domain of steven.price@arm.com designates 217.140.101.70 as permitted sender) client-ip=217.140.101.70; Authentication-Results: mx.google.com; spf=pass (google.com: domain of steven.price@arm.com designates 217.140.101.70 as permitted sender) smtp.mailfrom=steven.price@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D55CB374; Fri, 22 Mar 2019 03:37:18 -0700 (PDT) Received: from [10.1.196.69] (e112269-lin.cambridge.arm.com [10.1.196.69]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B5DB43F575; Fri, 22 Mar 2019 03:37:15 -0700 (PDT) Subject: Re: [PATCH v5 10/19] mm: pagewalk: Add p4d_entry() and pgd_entry() To: Mike Rapoport Cc: Mark Rutland , Dave Hansen , Arnd Bergmann , Ard Biesheuvel , Peter Zijlstra , Catalin Marinas , x86@kernel.org, Will Deacon , linux-kernel@vger.kernel.org, linux-mm@kvack.org, =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Ingo Molnar , Borislav Petkov , Andy Lutomirski , "H. Peter Anvin" , James Morse , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, "Liang, Kan" References: <20190321141953.31960-1-steven.price@arm.com> <20190321141953.31960-11-steven.price@arm.com> <20190321211510.GA27213@rapoport-lnx> <03f5ad0f-2450-c53f-b1e6-d2c0f2d4879c@arm.com> <20190322102930.GA24367@rapoport-lnx> From: Steven Price Message-ID: Date: Fri, 22 Mar 2019 10:37:14 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <20190322102930.GA24367@rapoport-lnx> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 22/03/2019 10:29, Mike Rapoport wrote: > On Fri, Mar 22, 2019 at 10:11:59AM +0000, Steven Price wrote: >> On 21/03/2019 21:15, Mike Rapoport wrote: >>> On Thu, Mar 21, 2019 at 02:19:44PM +0000, Steven Price wrote: >>>> pgd_entry() and pud_entry() were removed by commit 0b1fbfe50006c410 >>>> ("mm/pagewalk: remove pgd_entry() and pud_entry()") because there were >>>> no users. We're about to add users so reintroduce them, along with >>>> p4d_entry() as we now have 5 levels of tables. >>>> >>>> Note that commit a00cc7d9dd93d66a ("mm, x86: add support for >>>> PUD-sized transparent hugepages") already re-added pud_entry() but with >>>> different semantics to the other callbacks. Since there have never >>>> been upstream users of this, revert the semantics back to match the >>>> other callbacks. This means pud_entry() is called for all entries, not >>>> just transparent huge pages. >>>> >>>> Signed-off-by: Steven Price >>>> --- >>>> include/linux/mm.h | 9 ++++++--- >>>> mm/pagewalk.c | 27 ++++++++++++++++----------- >>>> 2 files changed, 22 insertions(+), 14 deletions(-) >>>> >>>> diff --git a/include/linux/mm.h b/include/linux/mm.h >>>> index 76769749b5a5..2983f2396a72 100644 >>>> --- a/include/linux/mm.h >>>> +++ b/include/linux/mm.h >>>> @@ -1367,10 +1367,9 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma, >>>> >>>> /** >>>> * mm_walk - callbacks for walk_page_range >>>> + * @pgd_entry: if set, called for each non-empty PGD (top-level) entry >>>> + * @p4d_entry: if set, called for each non-empty P4D (1st-level) entry >>> >>> IMHO, p4d implies the 4th level :) >> >> You have a good point there... I was simply working back from the >> existing definitions (below) of PTE:4th, PMD:3rd, PUD:2nd. But it's >> already somewhat broken by PGD:0th and my cop-out was calling it "top". >> >>> I think it would make more sense to start counting from PTE rather than >>> from PGD. Then it would be consistent across architectures with fewer >>> levels. >> >> It would also be the opposite way round to architectures such as Arm >> which number their levels, for example [1] refers to levels 0-3 (with 3 >> being PTE in Linux terms). > > By consistent I meant that for architectures with fewer levels we won't be > describing PTE as level 4 when the architecture only has 2 levels. Ah I see, although we've apparently been doing that for over a decade already[2] :) [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e6473092bd9116583ce9ab8cf1b6570e1aa6fc83 >> [1] >> https://developer.arm.com/docs/100940/latest/translation-tables-in-armv8-a >> >> Probably the least confusing thing is to drop the level numbers in >> brackets since I don't believe they directly match any architecture, and >> hopefully any user of the page walking code is already familiar with the >> P?D terms used by the kernel. > > That's a fair assumption :) > Still, maybe we keep your (top-level) for PGD and use (lowest level) for > PTE and drop those in the middle? Yes that's a good compromise. Thanks, Steve