linux-kernel - Re: [RFC PATCH 02/12] khugepaged: Generalize alloc_charge

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Message-ID: <acb63b4b-2f0d-45c4-859f-16a326d472a6@arm.com>
Date: Fri, 20 Dec 2024 17:45:04 +0000
From: Ryan Roberts <ryan.roberts@....com>
To: "Christoph Lameter (Ampere)" <cl@...two.org>
Cc: Matthew Wilcox <willy@...radead.org>, Dev Jain <dev.jain@....com>,
 akpm@...ux-foundation.org, david@...hat.com,
 kirill.shutemov@...ux.intel.com, anshuman.khandual@....com,
 catalin.marinas@....com, vbabka@...e.cz, mhocko@...e.com,
 apopple@...dia.com, dave.hansen@...ux.intel.com, will@...nel.org,
 baohua@...nel.org, jack@...e.cz, srivatsa@...il.mit.edu,
 haowenchao22@...il.com, hughd@...gle.com, aneesh.kumar@...nel.org,
 yang@...amperecomputing.com, peterx@...hat.com, ioworker0@...il.com,
 wangkefeng.wang@...wei.com, ziy@...dia.com, jglisse@...gle.com,
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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 02/12] khugepaged: Generalize alloc_charge_folio()

On 20/12/2024 17:41, Christoph Lameter (Ampere) wrote:
> On Tue, 17 Dec 2024, Ryan Roberts wrote:
> 
>> We previously decided that all existing THP stats would continue to only count
>> PMD-sized THP for fear of breaking userspace in subtle ways, and instead would
>> introduce new mTHP stats that can count for each order. We already have
>> MTHP_STAT_ANON_FAULT_ALLOC and MTHP_STAT_ANON_FAULT_FALLBACK (amongst others) so
>> these new stats fit the pattern well, IMHO.
> 
> Could we move all the stats somewhere into sysfs where we can get them by
> page order? /proc/vmstat keeps getting new counters.

This is exactly what has been done already for mthp stats. They live at:

/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/stats/.

So there is a directory per size, and there is a file per stat.