From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754552AbbBBBsH (ORCPT ); Sun, 1 Feb 2015 20:48:07 -0500 Received: from mail-pa0-f48.google.com ([209.85.220.48]:59211 "EHLO mail-pa0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753866AbbBBBsE (ORCPT ); Sun, 1 Feb 2015 20:48:04 -0500 Date: Mon, 2 Feb 2015 10:48:00 +0900 From: Sergey Senozhatsky To: Minchan Kim Cc: Sergey Senozhatsky , Sergey Senozhatsky , Andrew Morton , "linux-kernel@vger.kernel.org" , Linux-MM , Nitin Gupta , Jerome Marchand , Ganesh Mahendran Subject: Re: [PATCH v1 2/2] zram: remove init_lock in zram_make_request Message-ID: <20150202014800.GA6977@swordfish> References: <20150129020139.GB9672@blaptop> <20150129022241.GA2555@swordfish> <20150129052827.GB25462@blaptop> <20150129060604.GC2555@swordfish> <20150129063505.GA32331@blaptop> <20150129070835.GD2555@swordfish> <20150130144145.GA2840@blaptop> <20150201145036.GA1290@swordfish> <20150202013028.GB6402@blaptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150202013028.GB6402@blaptop> 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 Hello Minchan, On (02/02/15 10:30), Minchan Kim wrote: > > > static inline int init_done(struct zram *zram) > > > { > > > - return zram->meta != NULL; > > > + return zram->disksize != 0; > > > > we don't set ->disksize to 0 when create device. and I think > > it's better to use refcount here, but set it to 0 during device creation. > > (see the patch below) > > There was a reason I didn't use refcount there. > I should have written down it. > > We need something to prevent further I/O handling on other CPUs. > Otherwise, it's livelock. For example, new 'A' I/O rw path on CPU 1 > can see non-zero refcount if another CPU is going on rw. > Then, another new 'B' I/O rw path on CPU 2 can see non-zero refcount > if A I/O is going on. Then, another new 'C' I/O rw path on CPU 3 can > see non-zero refcount if B I/O is going on. Finally, 'A' IO is done > on CPU 1 and next I/O 'D' on CPU 1 can see non-zero refcount because > 'C' on CPU 3 is going on. Infinite loop. sure, I did think about this. and I actually didn't find any reason not to use ->refcount there. if user wants to reset the device, he first should umount it to make bdev->bd_holders check happy. and that's where IOs will be failed. so it makes sense to switch to ->refcount there, IMHO. > > here and later: > > we can't take zram_meta_get() first and then check for init_done(zram), > > because ->meta can be NULL, so it fill be ->NULL->refcount. > > True. > Actually, it was totally RFC I forgot adding the tag in the night but I can't > escape from my shame with the escuse. Thanks! no problem at all. you were throwing solutions all week long. > > > > > let's keep ->completion and ->refcount in zram and rename zram_meta_[get|put] > > to zram_[get|put]. > > Good idea but still want to name it as zram_meta_get/put because zram_get naming > might confuse struct zram's refcount rather than zram_meta. :) no objections. but I assume we agreed to keep ->io_done completion and ->refcount in zram. -ss