linux-kernel - Re: [RFC PATCH 01/12] khugepaged: Rename hpage_collapse_scan

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Message-ID: <0a33f5c1-c974-4d4a-94dd-6741399e186e@arm.com>
Date: Tue, 17 Dec 2024 06:43:34 +0000
From: Ryan Roberts <ryan.roberts@....com>
To: Matthew Wilcox <willy@...radead.org>, Dev Jain <dev.jain@....com>
Cc: akpm@...ux-foundation.org, david@...hat.com,
 kirill.shutemov@...ux.intel.com, anshuman.khandual@....com,
 catalin.marinas@....com, cl@...two.org, vbabka@...e.cz, mhocko@...e.com,
 apopple@...dia.com, dave.hansen@...ux.intel.com, will@...nel.org,
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 zhengqi.arch@...edance.com, jhubbard@...dia.com, 21cnbao@...il.com,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 01/12] khugepaged: Rename hpage_collapse_scan_pmd() ->
 ptes()

On 17/12/2024 04:18, Matthew Wilcox wrote:
> On Mon, Dec 16, 2024 at 10:20:54PM +0530, Dev Jain wrote:
>> -static int hpage_collapse_scan_pmd(struct mm_struct *mm,
>> +static int hpage_collapse_scan_ptes(struct mm_struct *mm,
> 
> i don't think this is necessary at all.  you're scanning a pmd.
> you might not be scanning in order to collapse to a pmd, but pmd
> is the level you're scanning at.
> 

Sorry Matthew, I don't really understand this statement. Prior to the change we
were scanning all PTE entries in a PTE table with the aim of collapsing to a PMD
entry. After the change we are scanning some PTE entries in a PTE table with the
aim of collapsing to either to a multi-PTE-mapped folio or a single-PMD-mapped
folio.

So personally I think "scan_pmd" was a misnomer even before the change - we are
scanning the ptes.