linux-kernel - Re: [PATCH v5 4/4] mm: correct the docs for thp_fault_alloc and thp_fault

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Message-ID: <2eae1247-02dc-47e1-b9b2-317a73937651@arm.com>
Date: Fri, 12 Apr 2024 11:21:06 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Barry Song <21cnbao@...il.com>, akpm@...ux-foundation.org,
 linux-mm@...ck.org
Cc: cerasuolodomenico@...il.com, chrisl@...nel.org, david@...hat.com,
 kasong@...cent.com, linux-kernel@...r.kernel.org, peterx@...hat.com,
 surenb@...gle.com, v-songbaohua@...o.com, willy@...radead.org,
 yosryahmed@...gle.com, yuzhao@...gle.com, corbet@....net
Subject: Re: [PATCH v5 4/4] mm: correct the docs for thp_fault_alloc and
 thp_fault_fallback

On 12/04/2024 08:37, Barry Song wrote:
> From: Barry Song <v-songbaohua@...o.com>
> 
> The documentation does not align with the code. In
> __do_huge_pmd_anonymous_page(), THP_FAULT_FALLBACK is incremented when
> mem_cgroup_charge() fails, despite the allocation succeeding, whereas
> THP_FAULT_ALLOC is only incremented after a successful charge.
> 
> Signed-off-by: Barry Song <v-songbaohua@...o.com>
> Cc: Chris Li <chrisl@...nel.org>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Domenico Cerasuolo <cerasuolodomenico@...il.com>
> Cc: Kairui Song <kasong@...cent.com>
> Cc: Matthew Wilcox (Oracle) <willy@...radead.org>
> Cc: Peter Xu <peterx@...hat.com>
> Cc: Ryan Roberts <ryan.roberts@....com>
> Cc: Suren Baghdasaryan <surenb@...gle.com>
> Cc: Yosry Ahmed <yosryahmed@...gle.com>
> Cc: Yu Zhao <yuzhao@...gle.com>
> Cc: Jonathan Corbet <corbet@....net>

Reviewed-by: Ryan Roberts <ryan.roberts@....com>

> ---
>  Documentation/admin-guide/mm/transhuge.rst | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
> index f436ff982f22..98e3a99ea780 100644
> --- a/Documentation/admin-guide/mm/transhuge.rst
> +++ b/Documentation/admin-guide/mm/transhuge.rst
> @@ -369,7 +369,7 @@ monitor how successfully the system is providing huge pages for use.
>  
>  thp_fault_alloc
>  	is incremented every time a huge page is successfully
> -	allocated to handle a page fault.
> +	allocated and charged to handle a page fault.
>  
>  thp_collapse_alloc
>  	is incremented by khugepaged when it has found
> @@ -377,7 +377,7 @@ thp_collapse_alloc
>  	successfully allocated a new huge page to store the data.
>  
>  thp_fault_fallback
> -	is incremented if a page fault fails to allocate
> +	is incremented if a page fault fails to allocate or charge
>  	a huge page and instead falls back to using small pages.
>  
>  thp_fault_fallback_charge