From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752607AbbA2BPt (ORCPT ); Wed, 28 Jan 2015 20:15:49 -0500 Received: from mail-pa0-f42.google.com ([209.85.220.42]:57653 "EHLO mail-pa0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751035AbbA2BPp (ORCPT ); Wed, 28 Jan 2015 20:15:45 -0500 Date: Thu, 29 Jan 2015 08:33:43 +0900 From: Minchan Kim To: Sergey Senozhatsky Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Nitin Gupta , Jerome Marchand , Ganesh Mahendran Subject: Re: [PATCH v1 2/2] zram: remove init_lock in zram_make_request Message-ID: <20150128233343.GC4706@blaptop> References: <1422432945-6764-1-git-send-email-minchan@kernel.org> <1422432945-6764-2-git-send-email-minchan@kernel.org> <20150128145651.GB965@swordfish> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150128145651.GB965@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 Wed, Jan 28, 2015 at 11:56:51PM +0900, Sergey Senozhatsky wrote: > On (01/28/15 17:15), Minchan Kim wrote: > > Admin could reset zram during I/O operation going on so we have > > used zram->init_lock as read-side lock in I/O path to prevent > > sudden zram meta freeing. > > > > However, the init_lock is really troublesome. > > We can't do call zram_meta_alloc under init_lock due to lockdep splat > > because zram_rw_page is one of the function under reclaim path and > > hold it as read_lock while other places in process context hold it > > as write_lock. So, we have used allocation out of the lock to avoid > > lockdep warn but it's not good for readability and fainally, I met > > another lockdep splat between init_lock and cpu_hotpulug from > > kmem_cache_destroy during wokring zsmalloc compaction. :( > > > > Yes, the ideal is to remove horrible init_lock of zram in rw path. > > This patch removes it in rw path and instead, put init_done bool > > variable to check initialization done with smp_[wmb|rmb] and > > srcu_[un]read_lock to prevent sudden zram meta freeing > > during I/O operation. > > > > Signed-off-by: Minchan Kim > > --- > > drivers/block/zram/zram_drv.c | 85 +++++++++++++++++++++++++++++++------------ > > drivers/block/zram/zram_drv.h | 5 +++ > > 2 files changed, 66 insertions(+), 24 deletions(-) > > > > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c > > index a598ada817f0..b33add453027 100644 > > --- a/drivers/block/zram/zram_drv.c > > +++ b/drivers/block/zram/zram_drv.c > > @@ -32,6 +32,7 @@ > > #include > > #include > > #include > > +#include > > > > #include "zram_drv.h" > > > > @@ -53,9 +54,31 @@ static ssize_t name##_show(struct device *d, \ > > } \ > > static DEVICE_ATTR_RO(name); > > > > -static inline int init_done(struct zram *zram) > > +static inline bool init_done(struct zram *zram) > > { > > - return zram->meta != NULL; > > + /* > > + * init_done can be used without holding zram->init_lock in > > + * read/write handler(ie, zram_make_request) but we should make sure > > + * that zram->init_done should set up after meta initialization is > > + * done. Look at setup_init_done. > > + */ > > + bool ret = zram->init_done; > > I don't like re-introduced ->init_done. > another idea... how about using `zram->disksize == 0' instead of > `->init_done' (previously `->meta != NULL')? should do the trick. It could be. > > > and I'm not sure I get this rmb... What makes you not sure? I think it's clear and common pattern for smp_[wmb|rmb]. :) > > -ss -- Kind regards, Minchan Kim