linux-kernel - Re: [PATCH] mm: khugepaged: fix the incorrect statistics when collapsing large file folios

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <C40089DF-C1D6-4A62-85FB-DAD3CC76844D@nvidia.com>
Date: Mon, 14 Oct 2024 11:42:22 -0400
From: Zi Yan <ziy@...dia.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: akpm@...ux-foundation.org, hughd@...gle.com, willy@...radead.org,
 david@...hat.com, 21cnbao@...il.com, ryan.roberts@....com,
 shy828301@...il.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: khugepaged: fix the incorrect statistics when
 collapsing large file folios

On 14 Oct 2024, at 6:24, Baolin Wang wrote:

> Khugepaged already supports collapsing file large folios (including shmem mTHP)
> by commit 7de856ffd007 ("mm: khugepaged: support shmem mTHP collapse"), and the
> control parameters in khugepaged: 'khugepaged_max_ptes_swap' and 'khugepaged_max_ptes_none',
> still compare based on PTE granularity to determine whether a file collapse is
> needed. However, the statistics for 'present' and 'swap' in hpage_collapse_scan_file()
> do not take into account the large folios, which may lead to incorrect judgments
> regarding the khugepaged_max_ptes_swap/none parameters, resulting in unnecessary
> file collapses.
>
> To fix this issue, take into account the large folios' statistics for 'present'
> and 'swap' variables in the hpage_collapse_scan_file().
>
> Fixes: 7de856ffd007 ("mm: khugepaged: support shmem mTHP collapse")
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> ---
>  mm/khugepaged.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index ba28ba09fe89..6f8d46d107b4 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -2267,7 +2267,7 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
>  			continue;
>
>  		if (xa_is_value(folio)) {
> -			++swap;
> +			swap += 1 << xas_get_order(&xas);

xas_get_order() scans xarry sibling entries to get the order. You probably
can call xas_get_order() outside the loop after rcu_read_lock() and use
the result inside, since xas order is not changed, right?

>  			if (cc->is_khugepaged &&
>  			    swap > khugepaged_max_ptes_swap) {
>  				result = SCAN_EXCEED_SWAP_PTE;
> @@ -2314,7 +2314,7 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
>  		 * is just too costly...
>  		 */
>
> -		present++;
> +		present += folio_nr_pages(folio);
>
>  		if (need_resched()) {
>  			xas_pause(&xas);
> -- 
> 2.39.3

Otherwise, LGTM. Thanks. Reviewed-by: Zi Yan <ziy@...dia.com>

--
Best Regards,
Yan, Zi

Download attachment "signature.asc" of type "application/pgp-signature" (855 bytes)