linux-kernel - Re: [RFC PATCH] mm: memblock: optimize memblock_find_in_range

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: <20130104150139.GB15633@mtj.dyndns.org>
Date:	Fri, 4 Jan 2013 10:01:39 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Lin Feng <linfeng@...fujitsu.com>
Cc:	akpm@...ux-foundation.org, mingo@...nel.org, yinghai@...nel.org,
	liwanp@...ux.vnet.ibm.com, benh@...nel.crashing.org,
	tangchen@...fujitsu.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] mm: memblock: optimize memblock_find_in_range_node()
 to minimize the search work

On Fri, Jan 04, 2013 at 05:24:53PM +0800, Lin Feng wrote:
> The memblock array is in ascending order and we traverse the memblock array in
> reverse order so we can add some simple check to reduce the search work.
> 
> Tejun fix a underflow bug in 5d53cb27d8, but I think we could break there for
> the same reason.
> 
> Cc: Tejun Heo <tj@...nel.org>
> Signed-off-by: Lin Feng <linfeng@...fujitsu.com>
> ---
>  mm/memblock.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 6259055..a710557 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -111,11 +111,18 @@ phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t start,
>  	end = max(start, end);
>  
>  	for_each_free_mem_range_reverse(i, nid, &this_start, &this_end, NULL) {
> +		/*
> +		 * exclude the regions out of the candidate range, since it's
> +		 * likely to find a suitable range, we ignore the worst case.
> +		 */
> +		if (this_start >= end)
> +			continue;
> +
>  		this_start = clamp(this_start, start, end);
>  		this_end = clamp(this_end, start, end);
>  
>  		if (this_end < size)
> -			continue;
> +			break;

I don't know.  This only saves looping when memblocks are below the
requested size, right?  I don't think it would matter in any way and
would prefer to keep the logic as simple as possible.

Thanks.

-- 
tejun
--
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/