linux-kernel - Re: [RFC 0/3] zram memory control enhance

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Date:	Wed, 13 Aug 2014 10:34:22 -0500
From:	Seth Jennings <sjennings@...iantweb.net>
To:	Minchan Kim <minchan@...nel.org>
Cc:	linux-mm@...ck.org, 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>
Subject: Re: [RFC 0/3] zram memory control enhance

On Tue, Aug 05, 2014 at 05:02:00PM +0900, Minchan Kim wrote:
> Notice! It's RFC. I didn't test at all but wanted to hear opinion
> during merge window when it's really busy time for Andrew so we could
> use the slack time to discuss without hurting him. ;-)
> 
> Patch 1 is to move pages_allocated in zsmalloc from size_class to zs_pool
> so zs_get_total_size_bytes of zsmalloc would be faster than old.
> zs_get_total_size_bytes could be used next patches frequently.
> 
> Patch 2 adds new feature which exports how many of bytes zsmalloc consumes
> during testing workload. Normally, before fixing the zram's disksize
> we have tested various workload and wanted to how many of bytes zram
> consumed.
> For it, we could poll mem_used_total of zram in userspace but the problem is
> when memory pressure is severe and heavy swap out happens suddenly then
> heavy swapin or exist while polling interval of user space is a few second,
> it could miss max memory size zram had consumed easily.
> With lack of information, user can set wrong disksize of zram so the result
> is OOM. So this patch adds max_mem_used for zram and zsmalloc supports it
> 
> Patch 3 is to limit zram memory consumption. Now, zram has no bound for
> memory usage so it could consume up all of system memory. It makes system
> memory control for platform hard so I have heard the feature several time.
> 
> Feedback is welcome!

One thing you might consider doing is moving zram to use the new zpool
API.  That way, when making changes that effect the zsmalloc API,
consideration for zpool, and by extension, zpool users like zswap are
also taken into account.

Seth

> 
> Minchan Kim (3):
>   zsmalloc: move pages_allocated to zs_pool
>   zsmalloc/zram: add zs_get_max_size_bytes and use it in zram
>   zram: limit memory size for zram
> 
>  Documentation/blockdev/zram.txt |  2 ++
>  drivers/block/zram/zram_drv.c   | 58 +++++++++++++++++++++++++++++++++++++++++
>  drivers/block/zram/zram_drv.h   |  1 +
>  include/linux/zsmalloc.h        |  1 +
>  mm/zsmalloc.c                   | 50 +++++++++++++++++++++++++----------
>  5 files changed, 98 insertions(+), 14 deletions(-)
> 
> -- 
> 2.0.0
> 
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