From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754381AbbCECEq (ORCPT ); Wed, 4 Mar 2015 21:04:46 -0500 Received: from mail-pd0-f176.google.com ([209.85.192.176]:42118 "EHLO mail-pd0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754048AbbCECEo (ORCPT ); Wed, 4 Mar 2015 21:04:44 -0500 Date: Thu, 5 Mar 2015 11:04:36 +0900 From: Minchan Kim To: Sergey Senozhatsky Cc: Andrew Morton , Sergey Senozhatsky , Nitin Gupta , linux-kernel@vger.kernel.org, Jerome Marchand Subject: Re: [PATCH 0/2] make automatic device_id generation possible Message-ID: <20150305020436.GB5041@blaptop> References: <1425478601-19141-1-git-send-email-sergey.senozhatsky@gmail.com> <20150305001954.GA9563@blaptop> <20150305005829.GC14927@swordfish> <20150305012043.GD14927@swordfish> <20150305013301.GA5041@blaptop> <20150305014752.GF14927@swordfish> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150305014752.GF14927@swordfish> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 05, 2015 at 10:47:52AM +0900, Sergey Senozhatsky wrote: > On (03/05/15 10:33), Minchan Kim wrote: > > > hm, I can think of a huge build server with tons of users. /dev/zram$(id -u) > > > created during user login and destroyed during logout. so users use theirs own > > > zram devices with predictable device ids (which also makes it simpler for admin) > > > for compilation/etc., and don't pressure hdds that much. > > > > They upgraded the system and from now on, one of app tries automatic > > id with zram for some reason. What happens if he gets some user id > > before the user login? The system should have fallback in the case of > > failing to create own userid assignment. > > we upgraded our scripts but landed some bugs there? it's up to particular > implementation. in your example, I assume, someone used zram with num_devices >= 1000? > that's impossible. current num_devices limitation is 32. and uid-s start from 1000. I meant it. If we support use-defined id and someone have used your idea so he can make zram per-user as uid. After a while, new application stats automatic id assignment so upcoming users can consume upcoming user id. yeah, automaic id will start from 0 so it's very rare to reach 1000 but who knows? My point is in your usecase, the script would be very fragile so it should have second plan like automatic id. > > these scripts should check if device has been created anyway, it just adds -EEXIST > check. in general "what if user space does something wrong" thing can be beaten by > "what if user space does everything right" argument. when script fails we just go > and fix that script, I guess. Yes, I believe finally the script will go automatic id if it was broken. So, why does we should support user-defined id if they finally should turn around from user-defined to automatic? > > -ss > > > > > Hmm, Coexisting specific and automatic id assign seem to be not a > > godd idea. -- Kind regards, Minchan Kim