Date: Mon, 3 Apr 2017 15:34:20 +0900
From: Minchan Kim <minchan@kernel.org>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, kernel-team@lge.com
Subject: Re: [PATCH 3/5] zram: use zram_slot_lock instead of raw
 bit_spin_lock op
Message-ID: <20170403063420.GA7713@bbox>
References: <1491196653-7388-1-git-send-email-minchan@kernel.org>
 <1491196653-7388-4-git-send-email-minchan@kernel.org>
 <20170403060858.GA17309@jagdpanzerIV.localdomain>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20170403060858.GA17309@jagdpanzerIV.localdomain>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1279
Lines: 40

Hi Sergey,

On Mon, Apr 03, 2017 at 03:08:58PM +0900, Sergey Senozhatsky wrote:
> Hello Minchan,
> 
> On (04/03/17 14:17), Minchan Kim wrote:
> > With this clean-up phase, I want to use zram's wrapper function
> > to lock table access which is more consistent with other zram's
> > functions.
> 
> which reminds me of...
> 
> there was a discussion a long time ago, -rt people absolutely
> hate bit spin_locks and they suggested us to replace it with
> normal spin_locks (and I promised to take a look at it, but
> got interrupted and never really returned back to it).
> 
> for !lockdep builds the impact is somewhat small; for lockdep
> builds we increase the memory usage, but
> 
> a) lockdep builds are debug builds by definition, no one runs lockdep
>    enabled kernels in production
> 
> b) we have lockdep in zram now, which is nice

It's really one I want to have.

> 
> c) spin_locks probably have better fairness guarantees

In fact, it wouldn't be an imporant because zram's slot lock contention
is not heavy.
> 
> 
> what do you think? can we, in this patch set, also replce bit
> spin_locks with a normal spin_lock?

With changing only zram side from bit_spin_lock to spin_lock,
it would be crippled. I mean zsmalloc should be changed, too
and it's really hard. :(