From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <owner-linux-mm@kvack.org>
Received: from psmtp.com (na3sys010amx202.postini.com [74.125.245.202])
	by kanga.kvack.org (Postfix) with SMTP id 4D42F6B0036
	for <linux-mm@kvack.org>; Thu,  4 Jul 2013 00:24:52 -0400 (EDT)
Date: Thu, 4 Jul 2013 13:24:50 +0900
From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Subject: Re: [RFC PATCH 0/5] Support multiple pages allocation
Message-ID: <20130704042450.GA7132@lge.com>
References: <1372840460-5571-1-git-send-email-iamjoonsoo.kim@lge.com>
 <20130703152824.GB30267@dhcp22.suse.cz>
 <51D44890.4080003@gmail.com>
 <51D44AE7.1090701@gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <51D44AE7.1090701@gmail.com>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: Zhang Yanfei <zhangyanfei.yes@gmail.com>
Cc: Michal Hocko <mhocko@suse.cz>, Andrew Morton <akpm@linux-foundation.org>, Mel Gorman <mgorman@suse.de>, David Rientjes <rientjes@google.com>, Glauber Costa <glommer@gmail.com>, Johannes Weiner <hannes@cmpxchg.org>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Rik van Riel <riel@redhat.com>, Hugh Dickins <hughd@google.com>, Minchan Kim <minchan@kernel.org>, Jiang Liu <jiang.liu@huawei.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org

On Thu, Jul 04, 2013 at 12:01:43AM +0800, Zhang Yanfei wrote:
> On 07/03/2013 11:51 PM, Zhang Yanfei wrote:
> > On 07/03/2013 11:28 PM, Michal Hocko wrote:
> >> On Wed 03-07-13 17:34:15, Joonsoo Kim wrote:
> >> [...]
> >>> For one page allocation at once, this patchset makes allocator slower than
> >>> before (-5%). 
> >>
> >> Slowing down the most used path is a no-go. Where does this slow down
> >> come from?
> > 
> > I guess, it might be: for one page allocation at once, comparing to the original
> > code, this patch adds two parameters nr_pages and pages and will do extra checks
> > for the parameter nr_pages in the allocation path.
> > 
> 
> If so, adding a separate path for the multiple allocations seems better.

Hello, all.

I modify the code for optimizing one page allocation via likely macro.
I attach a new one at the end of this mail.

In this case, performance degradation for one page allocation at once is -2.5%.
I guess, remained overhead comes from two added parameters.
Is it unreasonable cost to support this new feature?
I think that readahead path is one of the most used path, so this penalty looks
endurable. And after supporting this feature, we can find more use cases.

I will try to add a new function for the multiple allocations and test it. But,
IMHO, adding a new function is not good idea, because we should duplicate
various checks which are already in __alloc_pages_nodemask and even if
we introduce a new function, we cannot avoid to pass two parameters
to get_page_from_freelist(), so slight performance degradation on
one page allocation is inevitable. Anyway, I will do and test it.

Thanks.

-------------------------------8<----------------------------