From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f71.google.com (mail-pa0-f71.google.com [209.85.220.71]) by kanga.kvack.org (Postfix) with ESMTP id E26DB6B007E for ; Fri, 6 May 2016 00:36:55 -0400 (EDT) Received: by mail-pa0-f71.google.com with SMTP id xm6so142445290pab.3 for ; Thu, 05 May 2016 21:36:55 -0700 (PDT) Received: from lgeamrelo12.lge.com (LGEAMRELO12.lge.com. [156.147.23.52]) by mx.google.com with ESMTP id 3si15312158pfj.2.2016.05.05.21.36.54 for ; Thu, 05 May 2016 21:36:55 -0700 (PDT) Date: Fri, 6 May 2016 13:37:02 +0900 From: Minchan Kim Subject: Re: [PATCH] mm/zsmalloc: avoid unnecessary iteration in get_pages_per_zspage() Message-ID: <20160506043702.GB18573@bbox> References: <1462425447-13385-1-git-send-email-opensource.ganesh@gmail.com> <20160505100329.GA497@swordfish> <20160506030935.GA18573@bbox> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Ganesh Mahendran Cc: Sergey Senozhatsky , Nitin Gupta , Andrew Morton , Linux-MM , linux-kernel Hi Ganesh, On Fri, May 06, 2016 at 12:25:18PM +0800, Ganesh Mahendran wrote: > Hi, Minchan: > > 2016-05-06 11:09 GMT+08:00 Minchan Kim : > > On Thu, May 05, 2016 at 07:03:29PM +0900, Sergey Senozhatsky wrote: > >> 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 > > > > Thanks for the data, Sergey! > > > >> > >> 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. > >> > > > > I agree with Sergey. > > First of al, I appreciates your patch, Ganesh! But as Sergey pointed > > out, I don't see why it improves current zsmalloc. > > This patch does not obviously improve zsmalloc. > It just reduces unnecessary code path. > > From data provided by Sergey, 15 * (4 - 1) = 45 times loop will be avoided. > So 45 times of below caculation will be reduced: > --- > zspage_size = i * PAGE_SIZE; > waste = zspage_size % class_size; > usedpc = (zspage_size - waste) * 100 / zspage_size; > > if (usedpc > max_usedpc) { As well, it bloats code side without much gain. I don't think it's worth to do until someone really has trouble with slow zs_create_pool performance. add/remove: 0/0 grow/shrink: 1/0 up/down: 15/0 (15) function old new delta zs_create_pool 960 975 +15 > --- > > Thanks. > > > If you want to merge strongly, please convince me with more detail > > reason. > > > > Thanks. > > > > > >> -ss > >> > >> > Signed-off-by: Ganesh Mahendran > >> > Cc: Minchan Kim > >> > Cc: Nitin Gupta > >> > Cc: Sergey Senozhatsky > >> > --- > >> > 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 > >> > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org