From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753250AbaE1DyT (ORCPT ); Tue, 27 May 2014 23:54:19 -0400 Received: from mail-pa0-f51.google.com ([209.85.220.51]:64753 "EHLO mail-pa0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751713AbaE1DyS (ORCPT ); Tue, 27 May 2014 23:54:18 -0400 Date: Tue, 27 May 2014 20:53:00 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Chen Yucong cc: Shaohua Li , akpm@linux-foundation.org, ddstreet@ieee.org, mgorman@suse.de, k.kozlowski@samsung.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] swap: Avoid scanning invalidated region for cheap seek In-Reply-To: <1401069659-29589-1-git-send-email-slaoub@gmail.com> Message-ID: References: <1401069659-29589-1-git-send-email-slaoub@gmail.com> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 26 May 2014, Chen Yucong wrote: > For cheap seek, when we scan the region between si->lowset_bit > and scan_base, if san_base is greater than si->highest_bit, the > scan operation between si->highest_bit and scan_base is not > unnecessary. > > This patch can be used to avoid scanning invalidated region for > cheap seek. > > Signed-off-by: Chen Yucong I was going to suggest that you are adding a little code to a common path, in order to optimize a very unlikely case: which does not seem worthwhile to me. But digging a little deeper, I think you have hit upon something more interesting (though still in no need of your patch): it looks to me like that is not even a common path, but dead code. Shaohua, am I missing something, or does all SWP_SOLIDSTATE "seek is cheap" now go your si->cluster_info scan_swap_map_try_ssd_cluster() route? So that the "last_in_cluster < scan_base" loop in the body of scan_swap_map() is just redundant, and should have been deleted? Hugh > --- > mm/swapfile.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/mm/swapfile.c b/mm/swapfile.c > index beeeef8..7f0f27e 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -489,6 +489,7 @@ static unsigned long scan_swap_map(struct swap_info_struct *si, > { > unsigned long offset; > unsigned long scan_base; > + unsigned long upper_bound; > unsigned long last_in_cluster = 0; > int latency_ration = LATENCY_LIMIT; > > @@ -551,9 +552,11 @@ static unsigned long scan_swap_map(struct swap_info_struct *si, > > offset = si->lowest_bit; > last_in_cluster = offset + SWAPFILE_CLUSTER - 1; > + upper_bound = (scan_base <= si->highest_bit) ? > + scan_base : (si->highest_bit + 1); > > /* Locate the first empty (unaligned) cluster */ > - for (; last_in_cluster < scan_base; offset++) { > + for (; last_in_cluster < upper_bound; offset++) { > if (si->swap_map[offset]) > last_in_cluster = offset + SWAPFILE_CLUSTER; > else if (offset == last_in_cluster) { > -- > 1.7.10.4