linux-kernel - Re: [PATCH] mm: Do not allocate duplicate stack variables in shrink_page

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Message-ID: <20190131165215.i3iotkg64iz5ithp@ca-dmjordan1.us.oracle.com>
Date:   Thu, 31 Jan 2019 11:52:15 -0500
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     akpm@...ux-foundation.org, mhocko@...e.com, hannes@...xchg.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: Do not allocate duplicate stack variables in
 shrink_page_list()

On Thu, Jan 31, 2019 at 06:37:02PM +0300, Kirill Tkhai wrote:
> On path shrink_inactive_list() ---> shrink_page_list()
> we allocate stack variables for the statistics twice.
> This is completely useless, and this just consumes stack
> much more, then we really need.
> 
> The patch kills duplicate stack variables from shrink_page_list(),
> and this reduce stack usage and object file size significantly:
> 
> Stack usage:
> Before: vmscan.c:1122:22:shrink_page_list	648	static
> After:  vmscan.c:1122:22:shrink_page_list	616	static
> 
> Size of vmscan.o:
>          text	   data	    bss	    dec	    hex	filename
> Before: 56866	   4720	    128	  61714	   f112	mm/vmscan.o
> After:  56770	   4720	    128	  61618	   f0b2	mm/vmscan.o
> 
> Signed-off-by: Kirill Tkhai <ktkhai@...tuozzo.com>
> ---
>  mm/vmscan.c |   44 ++++++++++++++------------------------------
>  1 file changed, 14 insertions(+), 30 deletions(-)


> @@ -1534,6 +1517,7 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
>  		.priority = DEF_PRIORITY,
>  		.may_unmap = 1,
>  	};
> +	struct reclaim_stat dummy_stat;
>  	unsigned long ret;
>  	struct page *page, *next;
>  	LIST_HEAD(clean_pages);
> @@ -1547,7 +1531,7 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
>  	}
>  
>  	ret = shrink_page_list(&clean_pages, zone->zone_pgdat, &sc,
> -			TTU_IGNORE_ACCESS, NULL, true);
> +			TTU_IGNORE_ACCESS, &dummy_stat, true);
>  	list_splice(&clean_pages, page_list);
>  	mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE, -ret);
>  	return ret;

Stack usage stays the same coming from reclaim_clean_pages_from_list, with a
dummy variable added back after many were taken away in 3c710c1ad11b ("mm,
vmscan: extract shrink_page_list...").

But overall seems like a win to me.  You can add

Reviewed-by: Daniel Jordan <daniel.m.jordan@...cle.com>