From guent...@gmail.com Sun Oct 26 17:01:26 2014 X-Original-To: mayur...@devio.us Delivered-To: mayur...@devio.us X-Virus-Scanned: amavisd-new at devio.us Authentication-Results: wolfman.devio.us (amavisd-new); dkim=pass (2048-bit key) header.d=gmail.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=Y1DSnnU9Wt7FwAio1jfk5gZlL2jKuJHPCCViFatjQ70=; b=QGMPBl8DVLa7kSfBRI1pTbf0edQnJ8VAwk3s3vDKeXKBR9LTLzJ63504oLMcqdVDYy aC9ABaVEoT+K3LE31Gh1aJs5xIcfUgfznIWB3jgm8AzBXtsWET6eN5M0qDsuf8l9vy8j WoPgIQs1rag8xEALXfc0TgBS6lu6EYEPNxQJ6+gepqkhJkr/FZpPsBaz1DKJ7Yusk6Ip Hr/6QTjDnha2DAPeIEle7bpCYBnpQw5lFIYW1B/EhpAGYQnqLHl40NyQFCZwN1ohV4Nj Xa5t/cNwJwDLte70c+aVrpc+FA8TbzxJu1AdwoNvNkXISfb4R9c3ZUG1+4LekbHWisjL LBXg== MIME-Version: 1.0 X-Received: by 10.107.164.129 with SMTP id d1mr18706558ioj.37.1414357262671; Sun, 26 Oct 2014 14:01:02 -0700 (PDT) References: <20141026190245.b09d21b5...@wolfman.devio.us> Subject: Re: 64-bit amd64 : actual memory limitations? From: Philip Guenther <guent...@gmail.com> To: Mayuresh Kathe <mayur...@devio.us> Cc: OpenBSD misc <misc@openbsd.org> Content-Type: text/plain; charset=UTF-8
On Sun, Oct 26, 2014 at 12:02 PM, Mayuresh Kathe <mayur...@devio.us> wrote: > 64-bit supposedly supports upto 16 exabytes of memory ('ram'). > would such large capacities actually be possible to ue with > openbsd for amd64 architecture? > use-case: working with large in-memory storage for financial applications. Currently, in the amd64 pmap we only allocate a single PML4 slot for the 'direct' map, limiting the system to 512GB of physical memory. Multiplying that by a factor of 4 or even 64 would be easy, but lacking someone actually planning to *use and test* that it just hasn't been seen as worth the effort to do, verify the change in kva layout doesn't break some hidden assumption, etc. (IIRC, dlg@ did this once just to get a dmesg from a 2TB machine going to other, non-OpenBSD use.) There's an upper limit to that growth: there's only 256 PML4 slots for kva, from which this comes, so at some point the kva remaining for normal use and management would shrink too much and the whole pmap would need to be rethought... Philip Guenther thanks for the details, but, since i am nowhere close to being a systems programmer, would like to know if there's any chance such support might be added in, in the near future? thanks.