linux-kernel - Re: [PATCH] mm/zsmalloc: avoid unnecessary iteration in get_pages_per

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]

Date:	Thu, 5 May 2016 19:03:29 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Ganesh Mahendran <opensource.ganesh@...il.com>
Cc:	minchan@...nel.org, ngupta@...are.org,
	sergey.senozhatsky.work@...il.com, akpm@...ux-foundation.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/zsmalloc: avoid unnecessary iteration in
 get_pages_per_zspage()

On (05/05/16 13:17), Ganesh Mahendran wrote:
> if we find a zspage with usage == 100%, there is no need to
> try other zspages.

Hello,

well... we iterate there from 0 to 1<<2, which is not awfully
a lot to break it in the middle, and we do this only when we
initialize a new pool (for every size class).

the check is
 - true   15 times
 - false  492 times

so it _sort of_ feels like this new if-condition doesn't
buy us a lot, and most of the time it just sits there with
no particular gain. let's hear from Minchan.

	-ss

> Signed-off-by: Ganesh Mahendran <opensource.ganesh@...il.com>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Nitin Gupta <ngupta@...are.org>
> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
> ---
>  mm/zsmalloc.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index fda7177..310c7b0 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -765,6 +765,9 @@ static int get_pages_per_zspage(int class_size)
>  		if (usedpc > max_usedpc) {
>  			max_usedpc = usedpc;
>  			max_usedpc_order = i;
> +
> +			if (max_usedpc == 100)
> +				break;
>  		}
>  	}
>  
> -- 
> 1.7.9.5
>