From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Daniel Colascione Newsgroups: gmane.emacs.devel Subject: Re: When should ralloc.c be used? Date: Fri, 28 Oct 2016 02:52:19 -0700 Message-ID: References: <838ttfnmev.fsf@gnu.org> <837f8znk8f.fsf@gnu.org> <83zilvm2ud.fsf@gnu.org> <83r377m0i8.fsf@gnu.org> <83eg36n6v5.fsf@gnu.org> <83shrl523p.fsf@gnu.org> <83eg354ux3.fsf@gnu.org> <4f0c2868-d408-a5c4-d5a8-90dae750eb33@dancol.org> <878tt9ggdk.fsf@ritchie.wxcvbn.org> <83k2cssypt.fsf@gnu.org> <6350b2df-fde9-e716-d279-9f29438f8ee5@dancol.org> <83d1ikswsf.fsf@gnu.org> <7ab47b94-c662-1351-0dd3-ed5269842438@dancol.org> <83bmy4stax.fsf@gnu.org> NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Trace: blaine.gmane.org 1477648422 19053 195.159.176.226 (28 Oct 2016 09:53:42 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 28 Oct 2016 09:53:42 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 Cc: eggert@cs.ucla.edu, monnier@iro.umontreal.ca, emacs-devel@gnu.org To: Eli Zaretskii Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Fri Oct 28 11:53:38 2016 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1c03qh-0001yZ-Ad for ged-emacs-devel@m.gmane.org; Fri, 28 Oct 2016 11:53:19 +0200 Original-Received: from localhost ([::1]:47880 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1c03qj-0000lI-Rn for ged-emacs-devel@m.gmane.org; Fri, 28 Oct 2016 05:53:21 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:53706) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1c03pu-0000kF-JP for emacs-devel@gnu.org; Fri, 28 Oct 2016 05:52:31 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1c03pq-0007Yl-MJ for emacs-devel@gnu.org; Fri, 28 Oct 2016 05:52:30 -0400 Original-Received: from dancol.org ([2600:3c01::f03c:91ff:fedf:adf3]:44974) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1c03pq-0007YW-CX; Fri, 28 Oct 2016 05:52:26 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=dancol.org; s=x; h=Content-Transfer-Encoding:Content-Type:In-Reply-To:MIME-Version:Date:Message-ID:From:Cc:References:To:Subject; bh=lyY9YbbQc70guhvtHZEbL8LDF+a0fWI/Oe/yJCgjL2w=; b=FMI/i+Ax2W3cARdxa2KBroT+1220fSN2VBrsRkZfKmTCcHyws+fdVTGZI12aiqt4d7o9Q5R28GFYYLzKXm9zlO+eQzK++DF2yMO3ZhFtICcsyOZLsM/YbIO0FVgw5WAtf3cIL9E1yoQhSedda6PhKP0Oll9SDyHzE/tdUyWKEPJovwRvCWOhZz+QiBLRBupHfozDOhDJtxwKTHzcdn/8iqG2iPQD7CI42LpTNCQJb5m5BxUUWDUqpQi+VNks2PUm/rCdtDKCKAJW6B1R03kVg4CkRu5mTXSQoWByuKltPqEPb+ZwlYKuBOoLKuypHZYeHrXtOMxR2BBHJrV42ZIMPA==; Original-Received: from c-73-97-199-232.hsd1.wa.comcast.net ([73.97.199.232] helo=[192.168.1.173]) by dancol.org with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.84_2) (envelope-from ) id 1c03pn-0005ex-K5; Fri, 28 Oct 2016 02:52:23 -0700 In-Reply-To: <83bmy4stax.fsf@gnu.org> X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 2600:3c01::f03c:91ff:fedf:adf3 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Original-Sender: "Emacs-devel" Xref: news.gmane.org gmane.emacs.devel:208934 Archived-At: On 10/28/2016 02:43 AM, Eli Zaretskii wrote: >> Cc: monnier@iro.umontreal.ca, eggert@cs.ucla.edu, emacs-devel@gnu.org >> From: Daniel Colascione >> Date: Fri, 28 Oct 2016 01:44:33 -0700 >> >>>> Say you have a strict-accounting system with 1GB of RAM and 1GB of swap. >>>> I can write a program that reserves 20GB of address space. >>> >>> I thought such a reservation should fail, because you don't have >>> enough virtual memory for 20GB of addresses. IOW, I thought the >>> ability to reserve address space is restricted by the actual amount of >>> virtual memory available on the system at the time of the call. You >>> seem to say I was wrong. >> >> I'm not sure you're even wrong :-) What does "virtual memory" mean to >> you? > > Physical + swap, as usual. > >> When we allocate memory, we can consume two resources: address space and >> commit. That 100GB mmap above doesn't consume virtual memory, but it >> does consume address space. Address space is a finite resource, but >> usually much larger than commit, which is the sum of RAM and swap space. >> When you commit a page, the resource you're consuming is commit. > > If reserving a range of addresses doesn't necessarily mean they will > be later available for committing, then what is the purpose of > reserving them in the first place? What good does it do? Reserving address space is useful for making sure you have a contiguous range of virtual addresses that you can use later. > We have in w32heap.c:mmap_realloc code that attempts to commit pages > that were previously reserved. That code does recover from a failure > to commit, but such a failure is deemed unusual and causes special > warnings under debugger. I never saw these warnings happen, except > when we had bugs in that code. You seem to say that this is based on > false premises, and there's nothing unusual about MEM_COMMIT to fail > for the range of pages previously reserved with MEM_RESERVE. The MEM_COMMIT failure might be rare in practice --- systems have a lot of memory these days --- but MEM_COMMIT failing for a memory region previously reserved with MEM_RESERVE is perfectly legal. MEM_RESERVE does not stake a claim on the system's memory resources. It consumes only your own address space.