linux-kernel - Re: free_pages

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-Id: <20080107190822.b13c9f97.akpm@linux-foundation.org>
Date:	Mon, 7 Jan 2008 19:08:22 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Yinghai Lu" <yhlu.kernel@...il.com>
Cc:	"Christoph Lameter" <clameter@....com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Adrian Bunk" <bunk@...sta.de>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: free_pages_check

On Mon, 7 Jan 2008 18:43:46 -0800 "Yinghai Lu" <yhlu.kernel@...il.com> wrote:

> wonder why free_pages_check mm/page_alloc.c is using bit OR than logical OR
> 
> @@ -450,9 +450,9 @@ static inline void __free_one_page(struc
> 
>  static inline int free_pages_check(struct page *page)
>  {
> -       if (unlikely(page_mapcount(page) |
> -               (page->mapping != NULL)  |
> -               (page_count(page) != 0)  |
> +       if (unlikely(page_mapcount(page) ||
> +               (page->mapping != NULL)  ||
> +               (page_count(page) != 0)  ||
>                 (page->flags & (
>                         1 << PG_lru     |
>                         1 << PG_private |

It's a hack^Wtrick to avoid the generation of a series of not-taken
branches.  I don't recall anyone verifying that it is actually of any
benefit, but the theory is good.

The lack of a comment, however, is not.
--
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/