From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f172.google.com (mail-wi0-f172.google.com [209.85.212.172]) by kanga.kvack.org (Postfix) with ESMTP id AB8A56B0038 for ; Wed, 17 Sep 2014 09:56:23 -0400 (EDT) Received: by mail-wi0-f172.google.com with SMTP id e4so1284715wiv.5 for ; Wed, 17 Sep 2014 06:56:23 -0700 (PDT) Received: from casper.infradead.org (casper.infradead.org. [2001:770:15f::2]) by mx.google.com with ESMTPS id gn3si6763023wib.26.2014.09.17.06.56.21 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 17 Sep 2014 06:56:21 -0700 (PDT) Date: Wed, 17 Sep 2014 15:56:14 +0200 From: Peter Zijlstra Subject: Re: Best way to pin a page in ext4? Message-ID: <20140917135614.GJ2840@worktop.localdomain> References: <20140915185102.0944158037A@closure.thunk.org> <36321733-F488-49E3-8733-C6758F83DFA1@dilger.ca> <20140916180759.GI6205@thunk.org> 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: Hugh Dickins Cc: Theodore Ts'o , Andreas Dilger , Christoph Lameter , linux-mm , linux-ext4@vger.kernel.org On Tue, Sep 16, 2014 at 05:07:18PM -0700, Hugh Dickins wrote: > On the page migration issue: it's not quite as straightforward as > Christoph suggests. He and I agree completely that mlocked pages > should be migratable, but some real-time-minded people disagree: > so normal compaction is still forbidden to migrate mlocked pages in > the vanilla kernel (though we in Google patch that prohibition out). > So pinning by refcount is no worse for compaction than mlocking, > in the vanilla kernel. These realtime people are fully aware of this -- they should be at least, I've been telling them for years. Also, they would be very happy with means to actually pin pages -- as per the patches Christoph referred to. The advantage of also having mpin() and co is that we can migrate the memory into non-movable blocks before returning etc. In any case, I think we can (and should) change the behaviour of mlock to be migratable (possibly with an easy way to revert in -rt for migratory purposes until we get mpin sorted). -- 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