linux-kernel - Re: [PATCH 3/3] zram: add mem_used

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Date:	Thu, 14 Aug 2014 11:32:36 -0400
From:	David Horner <ds2horner@...il.com>
To:	Dan Streetman <ddstreet@...e.org>
Cc:	Minchan Kim <minchan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Jerome Marchand <jmarchan@...hat.com>, juno.choi@....com,
	seungho1.park@....com, Luigi Semenzato <semenzato@...gle.com>,
	Nitin Gupta <ngupta@...are.org>,
	Seth Jennings <sjennings@...iantweb.net>
Subject: Re: [PATCH 3/3] zram: add mem_used_max via sysfs

On Thu, Aug 14, 2014 at 11:09 AM, Dan Streetman <ddstreet@...e.org> wrote:
> On Wed, Aug 13, 2014 at 9:12 PM, Minchan Kim <minchan@...nel.org> wrote:
>> -       if (zram->limit_bytes &&
>> -               zs_get_total_size_bytes(meta->mem_pool) > zram->limit_bytes) {
>> +       total_bytes = zs_get_total_size_bytes(meta->mem_pool);
>> +       if (zram->limit_bytes && total_bytes > zram->limit_bytes) {
>
> do you need to take the init_lock to read limit_bytes here?  It could
> be getting changed between these checks...

There is no real danger in freeing with an error.
It is more timing than a race.

The max calculation is still ok because committed allocations are
added atomically.
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