Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753946AbdDJRrT (ORCPT ); Mon, 10 Apr 2017 13:47:19 -0400 Received: from mail-lf0-f50.google.com ([209.85.215.50]:32771 "EHLO mail-lf0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752689AbdDJRrR (ORCPT ); Mon, 10 Apr 2017 13:47:17 -0400 Subject: Re: [PATCH v3] lightnvm: physical block device (pblk) target To: Bart Van Assche , "jg@lightnvm.io" References: <1491591015-7554-1-git-send-email-javier@cnexlabs.com> <1491591015-7554-2-git-send-email-javier@cnexlabs.com> <1491839741.4199.7.camel@sandisk.com> Cc: "linux-kernel@vger.kernel.org" , "linux-block@vger.kernel.org" From: =?UTF-8?Q?Matias_Bj=c3=b8rling?= Message-ID: <7f8a2c0c-8a06-1036-164f-168924ec2a3f@lightnvm.io> Date: Mon, 10 Apr 2017 19:47:08 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <1491839741.4199.7.camel@sandisk.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2696 Lines: 56 On 04/10/2017 05:55 PM, Bart Van Assche wrote: > On Sun, 2017-04-09 at 11:15 +0200, Javier Gonz?lez wrote: >> On 8 Apr 2017, at 22.56, Bart Van Assche wrote: >>> On 04/07/17 11:50, Javier Gonz?lez wrote: >> struct ppa_addr, which is the physical address format is not affected, >> but pblk's internal L2P address representation (pblk_addr) is. You can >> see that the type either represents struct ppa_addr or ppa_addr_32. How >> would you define a type that can either be u64 or u32 with different bit >> offsets at run-time? Note that address conversions to this type is in >> the fast path and this format allows us to only use bit shifts. > > Selecting the appropriate representation at run-time would require to pass > pblk_addr by reference instead of by value to any function that expects a > pblk_addr. It would also require to have two versions of every data structure > that depends on pblk_addr and to use casts to convert to the appropritate > version. However, this approach is probably only worth to be implemented if > it doesn't introduce too much additional complexity. > Hi Bart, thanks for the feedback! I've spent the time today to implement it such that 32bit entries are used if the device addressing can fit. We do see a slight overhead, however not enough to be a deal-breaker. We'll post an updated version with the flag removed. >>>> +#ifdef CONFIG_NVM_DEBUG >>>> + atomic_add(nr_entries, &pblk->inflight_writes); >>>> + atomic_add(nr_entries, &pblk->req_writes); >>>> +#endif >>> >>> Has it been considered to use the "static key" feature such that >>> consistency checks can be enabled at run-time instead of having to >>> rebuild the kernel to enable CONFIG_NVM_DEBUG? >> >> I haven't considered it. I'll look into it. I would like to have this >> counters and the corresponding sysfs entry only available on debug mode >> since it allows us to have a good picture of the FTL state. > > If there are sysfs entries that depend on CONFIG_NVM_DEBUG then the static > key mechanism is probably not a good alternative for CONFIG_NVM_DEBUG. > >>> Has it been considered to add support for keeping a subset of the L2P >>> translation table in memory instead of keeping it in memory in its entirety? >> >> Yes. L2P caching is on our roadmap and will be included in the future. > > That's great. This will also help with reducing the time between discovery of > a lightnvm device and the time at which I/O can start since the L2P table must > be available before I/O can start. Definitely. I would love if one could jump in and implement it. We have a bunch of features that we want in before implementing a translation cache. > > Bart. >