linux-kernel - Re: [RFC PATCH 08/15] fs: proc: use PAGES_PER_SECTION for page offline checking period.

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Message-ID: <YQ5hIFZX02BMS+Yb@kernel.org>
Date:   Sat, 7 Aug 2021 13:32:00 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Zi Yan <ziy@...dia.com>
Cc:     David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
        Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Michal Hocko <mhocko@...nel.org>,
        John Hubbard <jhubbard@...dia.com>,
        linux-kernel@...r.kernel.org, Oscar Salvador <osalvador@...e.de>,
        Ying Chen <chenying.kernel@...edance.com>,
        Feng Zhou <zhoufeng.zf@...edance.com>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [RFC PATCH 08/15] fs: proc: use PAGES_PER_SECTION for page
 offline checking period.

On Thu, Aug 05, 2021 at 03:02:46PM -0400, Zi Yan wrote:
> From: Zi Yan <ziy@...dia.com>
> 
> It keeps the existing behavior after MAX_ORDER is increased beyond
> a section size.
> 
> Signed-off-by: Zi Yan <ziy@...dia.com>
> Cc: Mike Rapoport <rppt@...nel.org>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Ying Chen <chenying.kernel@...edance.com>
> Cc: Feng Zhou <zhoufeng.zf@...edance.com>
> Cc: linux-fsdevel@...r.kernel.org
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> ---
>  fs/proc/kcore.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
> index 3f148759a5fd..77b7ba48fb44 100644
> --- a/fs/proc/kcore.c
> +++ b/fs/proc/kcore.c
> @@ -486,7 +486,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
>  			}
>  		}
>  
> -		if (page_offline_frozen++ % MAX_ORDER_NR_PAGES == 0) {
> +		if (page_offline_frozen++ % PAGES_PER_SECTION == 0) {

The behavior changes here. E.g. with default configuration on x86 instead
of cond_resched() every 2M we get cond_resched() every 128M.

I'm not saying it's wrong but at least it deserves an explanation why.

>  			page_offline_thaw();
>  			cond_resched();
>  			page_offline_freeze();
> -- 
> 2.30.2
> 

-- 
Sincerely yours,
Mike.