linux-kernel - Re: [PATCH 2/4] mm, migrate: allocation new page lazyily in unmap_and

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 for Android: free password hash cracker in your pocket

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

Message-ID: <20130802194102.GV715@cmpxchg.org>
Date:	Fri, 2 Aug 2013 15:41:02 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Joonsoo Kim <js1304@...il.com>,
	Minchan Kim <minchan@...nel.org>, Mel Gorman <mgorman@...e.de>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 2/4] mm, migrate: allocation new page lazyily in
 unmap_and_move()

On Fri, Aug 02, 2013 at 11:07:57AM +0900, Joonsoo Kim wrote:
> We don't need a new page and then go out immediately if some condition
> is met. Allocation has overhead in comparison with some condition check,
> so allocating lazyily is preferable solution.
> 
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 6f0c244..86db87e 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -864,10 +864,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
>  {
>  	int rc = 0;
>  	int *result = NULL;
> -	struct page *newpage = get_new_page(page, private, &result);
> -
> -	if (!newpage)
> -		return -ENOMEM;
> +	struct page *newpage = NULL;
>  
>  	if (page_count(page) == 1) {
>  		/* page was freed from under us. So we are done. */
> @@ -878,6 +875,10 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
>  		if (unlikely(split_huge_page(page)))
>  			goto out;
>  
> +	newpage = get_new_page(page, private, &result);
> +	if (!newpage)
> +		return -ENOMEM;

get_new_page() sets up result to communicate error codes from the
following checks.  While the existing ones (page freed and thp split
failed) don't change rc, somebody else might add a condition whose
error code should be propagated back into *result but miss it.

Please leave get_new_page() where it is.  The win from this change is
not big enough to risk these problems.

Thanks!
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/