linux-kernel - Re: [PATCH] mm/page_alloc: cleanup __alloc_pages_direct

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Date:   Mon, 19 Aug 2019 15:50:41 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Pengfei Li <lpf.vector@...il.com>, akpm@...ux-foundation.org
Cc:     mhocko@...e.com, osalvador@...e.de, pavel.tatashin@...rosoft.com,
        mgorman@...hsingularity.net, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/page_alloc: cleanup __alloc_pages_direct_compact()

On 8/17/19 12:51 PM, Pengfei Li wrote:
> This patch cleans up the if(page).
> 
> No functional change.
> 
> Signed-off-by: Pengfei Li <lpf.vector@...il.com>

I don't see much benefit here. The indentation wasn't that bad that it
had to be reduced using goto. But the patch is not incorrect so I'm not
NACKing.

> ---
>  mm/page_alloc.c | 28 ++++++++++++++++------------
>  1 file changed, 16 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 272c6de1bf4e..51f056ac09f5 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3890,6 +3890,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
>  		enum compact_priority prio, enum compact_result *compact_result)
>  {
>  	struct page *page = NULL;
> +	struct zone *zone;
>  	unsigned long pflags;
>  	unsigned int noreclaim_flag;
>  
> @@ -3911,23 +3912,26 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
>  	 */
>  	count_vm_event(COMPACTSTALL);
>  
> -	/* Prep a captured page if available */
> -	if (page)
> +	if (page) {
> +		/* Prep a captured page if available */
>  		prep_new_page(page, order, gfp_mask, alloc_flags);
> -
> -	/* Try get a page from the freelist if available */
> -	if (!page)
> +	} else {
> +		/* Try get a page from the freelist if available */
>  		page = get_page_from_freelist(gfp_mask, order, alloc_flags, ac);
>  
> -	if (page) {
> -		struct zone *zone = page_zone(page);
> -
> -		zone->compact_blockskip_flush = false;
> -		compaction_defer_reset(zone, order, true);
> -		count_vm_event(COMPACTSUCCESS);
> -		return page;
> +		if (!page)
> +			goto failed;
>  	}
>  
> +	zone = page_zone(page);
> +	zone->compact_blockskip_flush = false;
> +	compaction_defer_reset(zone, order, true);
> +
> +	count_vm_event(COMPACTSUCCESS);
> +
> +	return page;
> +
> +failed:
>  	/*
>  	 * It's bad if compaction run occurs and fails. The most likely reason
>  	 * is that pages exist, but not enough to satisfy watermarks.
>