From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755026AbaEHQCS (ORCPT ); Thu, 8 May 2014 12:02:18 -0400 Received: from mga02.intel.com ([134.134.136.20]:50178 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752733AbaEHQCR (ORCPT ); Thu, 8 May 2014 12:02:17 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.97,1010,1389772800"; d="scan'208";a="537157694" From: "Kirill A. Shutemov" To: Armin Rigo Cc: "Kirill A. Shutemov" , Andrew Morton , Linus Torvalds , linux-kernel@vger.kernel.org, linux-mm@kvack.org, peterz@infradead.org, mingo@kernel.org In-Reply-To: References: <1399552888-11024-1-git-send-email-kirill.shutemov@linux.intel.com> Subject: Re: [PATCHv2 0/2] remap_file_pages() decommission Content-Transfer-Encoding: 7bit Message-Id: <20140508160205.A0EC7E009B@blue.fi.intel.com> Date: Thu, 8 May 2014 19:02:05 +0300 (EEST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Armin Rigo wrote: > Hi everybody, > > Here is a note from the PyPy project (mentioned earlier in this > thread, and at https://lwn.net/Articles/587923/ ). > > Yes, we use remap_file_pages() heavily on the x86-64 architecture. > However, the individual calls to remap_file_pages() are not > performance-critical, so it is easy to switch to using multiple > mmap()s. We need to perform more measurements to know exactly what > the overhead would be, in terms notably of kernel memory. > > However, an issue with that approach is the upper bound on the number > of VMAs. By default, it is not large enough. Right now, it is > possible to remap say 10% of the individual pages from an anonymous > mmap of multiple GBs in size; but doing so with individual calls to > mmap hits this arbitrary limit. The limit is not totaly random. We use ELF format for coredumps and ELF has limitation (16-bit field) on number of sections it can store. With ELF extended numbering we can bypass 16-bit limit, but some userspace can be surprised by that. > I have no particular weight to give > for or against keeping remap_file_pages() in the kernel, but if it is > removed or emulated, it would be a plus if the programs would run on a > machine with the default configuration --- i.e. if you remove or > emulate remap_file_pages(), please increase the default limit as well. It's fine to me. Andrew? -- Kirill A. Shutemov