linux-kernel - Re: [PATCH 3/5] zram: use zram_slot_lock instead of raw bit_spin

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Message-ID: <20170403080632.GB17309@jagdpanzerIV.localdomain>
Date:   Mon, 3 Apr 2017 17:06:32 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        kernel-team@....com
Subject: Re: [PATCH 3/5] zram: use zram_slot_lock instead of raw
 bit_spin_lock op

On (04/03/17 15:34), Minchan Kim wrote:
[..]
> > 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.

mostly agree. I think (and I may be mistaken) direct IO
causes contention; but direct IO is probably not a usual
zram workload.

> > 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. :(

hm, good point.

	-ss