linux-kernel - Re: [PATCH] smaps: count large pages smaller than PMD size to anonymous

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Message-ID: <926c6f86-82c6-41bb-a24d-5418163d5c5e@redhat.com>
Date: Tue, 3 Dec 2024 15:17:20 +0100
From: David Hildenbrand <david@...hat.com>
To: Wenchao Hao <haowenchao22@...il.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Matthew Wilcox <willy@...radead.org>, Oscar Salvador <osalvador@...e.de>,
 Muhammad Usama Anjum <usama.anjum@...labora.com>,
 Andrii Nakryiko <andrii@...nel.org>, Ryan Roberts <ryan.roberts@....com>,
 Peter Xu <peterx@...hat.com>, Barry Song <21cnbao@...il.com>,
 linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 linux-mm@...ck.org
Subject: Re: [PATCH] smaps: count large pages smaller than PMD size to
 anonymous_thp

On 03.12.24 14:49, Wenchao Hao wrote:
> Currently, /proc/xxx/smaps reports the size of anonymous huge pages for
> each VMA, but it does not include large pages smaller than PMD size.
> 
> This patch adds the statistics of anonymous huge pages allocated by
> mTHP which is smaller than PMD size to AnonHugePages field in smaps.
> 
> Signed-off-by: Wenchao Hao <haowenchao22@...il.com>
> ---
>   fs/proc/task_mmu.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 38a5a3e9cba2..b655011627d8 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -717,6 +717,12 @@ static void smaps_account(struct mem_size_stats *mss, struct page *page,
>   		if (!folio_test_swapbacked(folio) && !dirty &&
>   		    !folio_test_dirty(folio))
>   			mss->lazyfree += size;
> +
> +		/*
> +		 * Count large pages smaller than PMD size to anonymous_thp
> +		 */
> +		if (!compound && PageHead(page) && folio_order(folio))
> +			mss->anonymous_thp += folio_size(folio);
>   	}
>   
>   	if (folio_test_ksm(folio))


I think we decided to leave this (and /proc/meminfo) be one of the last
interfaces where this is only concerned with PMD-sized ones:

Documentation/admin-guide/mm/transhuge.rst:

The number of PMD-sized anonymous transparent huge pages currently used by the
system is available by reading the AnonHugePages field in ``/proc/meminfo``.
To identify what applications are using PMD-sized anonymous transparent huge
pages, it is necessary to read ``/proc/PID/smaps`` and count the AnonHugePages
fields for each mapping. (Note that AnonHugePages only applies to traditional
PMD-sized THP for historical reasons and should have been called
AnonHugePmdMapped).



-- 
Cheers,

David / dhildenb