linux-kernel - Re: [RFC 2/3] zsmalloc/zram: add zs_get_max_size

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Date:	Thu, 7 Aug 2014 22:47:42 -0400
From:	David Horner <ds2horner@...il.com>
To:	minchan@...nel.org
Cc:	linux-kernel-mm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 2/3] zsmalloc/zram: add zs_get_max_size_bytes and use it in zram

 [2/3]


 But why isn't mem_used_max writable? (save tearing down and rebuilding
 device to reset max)

 static DEVICE_ATTR(mem_used_max, S_IRUGO, mem_used_max_show, NULL);

 static DEVICE_ATTR(mem_used_max, S_IRUGO | S_IWUSR, mem_used_max_show, NULL);

   with a check in the store() that the new value is positive and less
than current max?


 I'm also a little puzzled why there is a new API zs_get_max_size_bytes if
 the data is accessible through sysfs?
 Especially if max limit will be (as you propose for [3/3]) through accessed
 through zsmalloc and hence zram needn't access.



  [3/3]
 I concur that the zram limit is best implemented in zsmalloc.
 I am looking forward to that revised code.


> From: Minchan Kim <minchan <at> kernel.org>
> Subject: [RFC 2/3] zsmalloc/zram: add zs_get_max_size_bytes and use it in
> zram
> <http://news.gmane.org/find-root.php?message_id=1407225723%2d23754%2d3%2dgit%2dsend%2demail%2dminchan%40kernel.org>
> Newsgroups: gmane.linux.kernel.mm
> <http://news.gmane.org/gmane.linux.kernel.mm>, gmane.linux.kernel
> <http://news.gmane.org/gmane.linux.kernel>
> Date: 2014-08-05 08:02:02 GMT (5 hours and 4 minutes ago)
>
> Normally, zram user can get maximum memory zsmalloc consumed via
> polling mem_used_total with sysfs in userspace.
>
> But it has a critical problem because user can miss peak memory
> usage during update interval so that gap between them could be
> huge when memory pressure is really heavy.
>
> This patch adds new API zs_get_max_size_bytes in zsmalloc so
> user(ex, zram) doesn't need to poll in short interval to get
> exact value.
>
> User can just see max memory usage once his test workload is
> done. It's pretty handy and accurate.
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