From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753864Ab3CRLBi (ORCPT ); Mon, 18 Mar 2013 07:01:38 -0400 Received: from cantor2.suse.de ([195.135.220.15]:34414 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752471Ab3CRLBh (ORCPT ); Mon, 18 Mar 2013 07:01:37 -0400 Date: Mon, 18 Mar 2013 12:01:36 +0100 From: Michal Hocko To: "K. Y. Srinivasan" Cc: gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, devel@linuxdriverproject.org, olaf@aepfle.de, apw@canonical.com, andi@firstfloor.org, akpm@linux-foundation.org, linux-mm@kvack.org, kamezawa.hiroyuki@gmail.com, hannes@cmpxchg.org, yinghan@google.com Subject: Re: [PATCH 2/2] Drivers: hv: balloon: Support 2M page allocations for ballooning Message-ID: <20130318110136.GH10192@dhcp22.suse.cz> References: <1363470088-24565-1-git-send-email-kys@microsoft.com> <1363470125-24606-1-git-send-email-kys@microsoft.com> <1363470125-24606-2-git-send-email-kys@microsoft.com> <20130318105257.GG10192@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130318105257.GG10192@dhcp22.suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 18-03-13 11:52:57, Michal Hocko wrote: > On Sat 16-03-13 14:42:05, K. Y. Srinivasan wrote: > > While ballooning memory out of the guest, attempt 2M allocations first. > > If 2M allocations fail, then go for 4K allocations. In cases where we > > have performed 2M allocations, split this 2M page so that we can free this > > page at 4K granularity (when the host returns the memory). > > Maybe I am missing something but what is the advantage of 2M allocation > when you split it up immediately so you are not using it as a huge page? OK, it seems that Patch 1/2 says some advantages. That description should be part of this patch IMO. You are saying that a) it reduces fragmentation on the host b) it makes ballooning more effective. Have you measured any effects on the ability to allocate huge pages on the host? What prevents from depleting high order pages on the host with many guests? Also have you measured any effect on THP allocation success rate on the host? Could you clarify how this helps ballooning when you split the page right after you allocate it? -- Michal Hocko SUSE Labs