From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S933847AbdACEec (ORCPT <rfc822;w@1wt.eu>);
        Mon, 2 Jan 2017 23:34:32 -0500
Received: from LGEAMRELO12.lge.com ([156.147.23.52]:50738 "EHLO
        lgeamrelo12.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1756140AbdACEe0 (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 2 Jan 2017 23:34:26 -0500
X-Original-SENDERIP: 156.147.1.126
X-Original-MAILFROM: minchan@kernel.org
X-Original-SENDERIP: 165.244.249.25
X-Original-MAILFROM: minchan@kernel.org
X-Original-SENDERIP: 10.177.223.161
X-Original-MAILFROM: minchan@kernel.org
Date: Tue, 3 Jan 2017 13:34:11 +0900
From: Minchan Kim <minchan@kernel.org>
To: Jan Kara <jack@suse.cz>
CC: Tim Chen <tim.c.chen@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ying Huang <ying.huang@intel.com>, <dave.hansen@intel.com>,
        <ak@linux.intel.com>, <aaron.lu@intel.com>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>, Hugh Dickins <hughd@google.com>,
        Shaohua Li <shli@kernel.org>, Rik van Riel <riel@redhat.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@kernel.org>,
        Hillf Danton <hillf.zj@alibaba-inc.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Peter Zijlstra <peterz@infradead.org>,
        Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH v4 0/9] mm/swap: Regular page swap optimizations
Message-ID: <20170103043411.GA15657@bbox>
References: <cover.1481317367.git.tim.c.chen@linux.intel.com>
 <20161227074503.GA10616@bbox>
 <20170102154841.GG18058@quack2.suse.cz>
MIME-Version: 1.0
In-Reply-To: <20170102154841.GG18058@quack2.suse.cz>
User-Agent: Mutt/1.5.24 (2015-08-30)
X-MIMETrack: Itemize by SMTP Server on LGEKRMHUB08/LGE/LG Group(Release 8.5.3FP6|November
 21, 2013) at 2017/01/03 13:34:17,
        Serialize by Router on LGEKRMHUB08/LGE/LG Group(Release 8.5.3FP6|November
 21, 2013) at 2017/01/03 13:34:17,
        Serialize complete at 2017/01/03 13:34:17
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Hi Jan,

On Mon, Jan 02, 2017 at 04:48:41PM +0100, Jan Kara wrote:
> Hi,
> 
> On Tue 27-12-16 16:45:03, Minchan Kim wrote:
> > > Patch 3 splits the swap cache radix tree into 64MB chunks, reducing
> > >         the rate that we have to contende for the radix tree.
> > 
> > To me, it's rather hacky. I think it might be common problem for page cache
> > so can we think another generalized way like range_lock? Ccing Jan.
> 
> I agree on the hackyness of the patch and that page cache would suffer with
> the same contention (although the files are usually smaller than swap so it
> would not be that visible I guess). But I don't see how range lock would
> help here - we need to serialize modifications of the tree structure itself
> and that is difficult to achieve with the range lock. So what you would
> need is either a different data structure for tracking swap cache entries
> or a finer grained locking of the radix tree.

Thanks for the comment, Jan.

I think there are more general options. One is to shrink batching pages like
Mel and Tim had approached.

https://patchwork.kernel.org/patch/9008421/
https://patchwork.kernel.org/patch/9322793/

Or concurrent page cache by peter.

https://www.kernel.org/doc/ols/2007/ols2007v2-pages-311-318.pdf

Ccing Nick who might have an interest on lockless page cache.

Thanks.