From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f70.google.com (mail-wm0-f70.google.com [74.125.82.70]) by kanga.kvack.org (Postfix) with ESMTP id A4B5528026B for ; Tue, 27 Sep 2016 04:54:15 -0400 (EDT) Received: by mail-wm0-f70.google.com with SMTP id l138so322191wmg.3 for ; Tue, 27 Sep 2016 01:54:15 -0700 (PDT) Received: from outbound-smtp02.blacknight.com (outbound-smtp02.blacknight.com. [81.17.249.8]) by mx.google.com with ESMTPS id ju8si1270609wjb.191.2016.09.27.01.54.14 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 27 Sep 2016 01:54:14 -0700 (PDT) Received: from mail.blacknight.com (pemlinmail05.blacknight.ie [81.17.254.26]) by outbound-smtp02.blacknight.com (Postfix) with ESMTPS id 1700098E00 for ; Tue, 27 Sep 2016 08:54:14 +0000 (UTC) Date: Tue, 27 Sep 2016 09:54:12 +0100 From: Mel Gorman Subject: Re: page_waitqueue() considered harmful Message-ID: <20160927085412.GD2838@techsingularity.net> References: <20160927073055.GM2794@worktop> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20160927073055.GM2794@worktop> Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra Cc: Linus Torvalds , Andrew Morton , "Kirill A. Shutemov" , Johannes Weiner , Jan Kara , Rik van Riel , linux-mm On Tue, Sep 27, 2016 at 09:30:55AM +0200, Peter Zijlstra wrote: > > Also, if those bitlock ops had a different bit that showed contention, > > we could actually skip *all* of this, and just see that "oh, nobody is > > waiting on this page anyway, so there's no point in looking up those > > wait queues". We don't have that many "__wait_on_bit()" users, maybe > > we could say that the bitlocks do have to haev *two* bits: one for the > > lock bit itself, and one for "there is contention". > > That would be fairly simple to implement, the difficulty would be > actually getting a page-flag to use for this. We're running pretty low > in available bits :/ Simple is relative unless I drastically overcomplicated things and it wouldn't be the first time. 64-bit only side-steps the page flag issue as long as we can live with that. -- Mel Gorman SUSE Labs -- 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