linux-kernel - Re: [PATCH v5 00/25] Transparent Contiguous PTEs for User Mappings

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Date: Thu, 8 Feb 2024 17:34:33 +0000
From: Mark Rutland <mark.rutland@....com>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
	Marc Zyngier <maz@...nel.org>, James Morse <james.morse@....com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matthew Wilcox <willy@...radead.org>,
	David Hildenbrand <david@...hat.com>,
	Kefeng Wang <wangkefeng.wang@...wei.com>,
	John Hubbard <jhubbard@...dia.com>, Zi Yan <ziy@...dia.com>,
	Barry Song <21cnbao@...il.com>,
	Alistair Popple <apopple@...dia.com>,
	Yang Shi <shy828301@...il.com>, Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	"Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
	"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	linux-arm-kernel@...ts.infradead.org, x86@...nel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 00/25] Transparent Contiguous PTEs for User Mappings

On Fri, Feb 02, 2024 at 08:07:31AM +0000, Ryan Roberts wrote:
> Hi All,

Hi Ryan,

I assume this is the same as your 'features/granule_perf/contpte-lkml_v' branch
on https://gitlab.arm.com/linux-arm/linux-rr/

I've taken a quick look, and I have a few initial/superficial comments before
digging into the detail on the important changes.

> Patch Layout
> ============
> 
> In this version, I've split the patches to better show each optimization:
> 
>   - 1-2:    mm prep: misc code and docs cleanups

I'm not confident enough to comment on patch 2, but these look reasonable to
me.

>   - 3-8:    mm,arm,arm64,powerpc,x86 prep: Replace pte_next_pfn() with more
>             general pte_advance_pfn()

These look fine to me.

>   - 9-18:   arm64 prep: Refactor ptep helpers into new layer

The result of patches 9-17 looks good to me, but the intermediate stages where
some functions are converted is a bit odd, and it's a bit painful for review
since you need to skip ahead a few patches to see the end result to tell that
the conversions are consistent and complete.

IMO it'd be easier for review if that were three patches:

1) Convert READ_ONCE() -> ptep_get()
2) Convert set_pte_at() -> set_ptes()
3) All the "New layer" renames and addition of the trivial wrappers

Patch 18 looks fine to me.

>   - 19:     functional contpte implementation
>   - 20-25:  various optimizations on top of the contpte implementation

I'll try to dig into these over the next few days.

Mark.