From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752081AbYE1NxA (ORCPT ); Wed, 28 May 2008 09:53:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750989AbYE1Nww (ORCPT ); Wed, 28 May 2008 09:52:52 -0400 Received: from e5.ny.us.ibm.com ([32.97.182.145]:58660 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750909AbYE1Nwv (ORCPT ); Wed, 28 May 2008 09:52:51 -0400 Subject: Re: [PATCH 2/3] Reserve huge pages for reliable MAP_PRIVATE hugetlbfs mappings until fork() From: Adam Litke To: Mel Gorman Cc: akpm@linux-foundation.org, abh@cray.com, dean@arctic.org, linux-kernel@vger.kernel.org, wli@holomorphy.com, dwg@au1.ibm.com, linux-mm@kvack.org, andi@firstfloor.org, kenchen@google.com, apw@shadowen.org In-Reply-To: <20080527185108.16194.87892.sendpatchset@skynet.skynet.ie> References: <20080527185028.16194.57978.sendpatchset@skynet.skynet.ie> <20080527185108.16194.87892.sendpatchset@skynet.skynet.ie> Content-Type: text/plain Organization: IBM Date: Wed, 28 May 2008 08:52:44 -0500 Message-Id: <1211982764.12036.58.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.22.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2008-05-27 at 19:51 +0100, Mel Gorman wrote: > This patch reserves huge pages at mmap() time for MAP_PRIVATE mappings in a > similar manner to the reservations taken for MAP_SHARED mappings. The reserve count is > accounted both globally and on a per-VMA basis for private mappings. This > guarantees that a process that successfully calls mmap() will successfully > fault all pages in the future unless fork() is called. > > The characteristics of private mappings of hugetlbfs files behaviour after > this patch are; > > 1. The process calling mmap() is guaranteed to succeed all future faults until > it forks(). > 2. On fork(), the parent may die due to SIGKILL on writes to the private > mapping if enough pages are not available for the COW. For reasonably > reliable behaviour in the face of a small huge page pool, children of > hugepage-aware processes should not reference the mappings; such as > might occur when fork()ing to exec(). > 3. On fork(), the child VMAs inherit no reserves. Reads on pages already > faulted by the parent will succeed. Successful writes will depend on enough > huge pages being free in the pool. > 4. Quotas of the hugetlbfs mount are checked at reserve time for the mapper > and at fault time otherwise. > > Before this patch, all reads or writes in the child potentially needs page > allocations that can later lead to the death of the parent. This applies > to reads and writes of uninstantiated pages as well as COW. After the > patch it is only a write to an instantiated page that causes problems. > > Signed-off-by: Mel Gorman Acked-by: Adam Litke -- Adam Litke - (agl at us.ibm.com) IBM Linux Technology Center