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Subject: Re: [PATCH] mm: page_owner: fetch backtrace only for tracked pages
To:     Sergei Trofimovich <slyfox@gentoo.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org
References: <20210401212445.3534721-1-slyfox@gentoo.org>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <0c18e497-07d1-887f-e49e-b6315f396ab8@suse.cz>
Date:   Wed, 7 Apr 2021 17:49:14 +0200
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On 4/1/21 11:24 PM, Sergei Trofimovich wrote:
> Very minor optimization.

I'm not entirely sure about accuracy of "only for tracked pages". Missing
page_ext is something I'm not even sure how possible it is in practice, probably
just an error condition (failed to be allocated?). Or did you observe this in
practice? But anyway, the change is not wrong.

> CC: Andrew Morton <akpm@linux-foundation.org>
> CC: linux-mm@kvack.org
> Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  mm/page_owner.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 63e4ecaba97b..7147fd34a948 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -140,14 +140,14 @@ void __reset_page_owner(struct page *page, unsigned int order)
>  {
>  	int i;
>  	struct page_ext *page_ext;
> -	depot_stack_handle_t handle = 0;
> +	depot_stack_handle_t handle;
>  	struct page_owner *page_owner;
>  
> -	handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
> -
>  	page_ext = lookup_page_ext(page);
>  	if (unlikely(!page_ext))
>  		return;
> +
> +	handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
>  	for (i = 0; i < (1 << order); i++) {
>  		__clear_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags);
>  		page_owner = get_page_owner(page_ext);
>