linux-kernel - Re: [PATCH 2/2] zram: user per-cpu compression streams

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Date:	Tue, 3 May 2016 14:57:15 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] zram: user per-cpu compression streams

On (05/03/16 14:40), Minchan Kim wrote:
[..]
> > At least, we need sanity check code, still?
> > Otherwise, user can echo "garbage" > /sys/xxx/max_comp_stream" and then
> > cat /sys/xxx/max_comp_stream returns num_online_cpus.
> 
> One more thing,
> 
> User:
> echo 4 > /sys/xxx/max_comp_stream"
> cat /sys/xxx/max_comp_streams
> 8

sure, it can also be

cat /sys/xxx/max_comp_streams
5
cat /sys/xxx/max_comp_streams
6
cat /sys/xxx/max_comp_streams
7
cat /sys/xxx/max_comp_streams
3

depending on the availability of CPUs. but why would user space
constantly check max_comp_streams?

> which is rather weird?
> 
> We should keep user's value and return it to user although it's techically
> lying. IMO, it would be best way to prevent confusing for user until we
> removes max_comp_streams finally.

well, I preferred to show the actual state of the device. besides,
does anyone really do

	write buffer to file
	if (success)
		read from file and compare with the buffer

?

	-ss