linux-kernel - Re: [PATCH v6 0/5] zram/zsmalloc promotion

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Date:	Mon, 19 Aug 2013 14:07:04 +0800
From:	Bob Liu <bob.liu@...cle.com>
To:	Luigi Semenzato <semenzato@...gle.com>
CC:	Minchan Kim <minchan@...nel.org>, Mel Gorman <mgorman@...e.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Nitin Gupta <ngupta@...are.org>,
	Konrad Rzeszutek Wilk <konrad@...nok.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Pekka Enberg <penberg@...helsinki.fi>,
	Sonny Rao <sonnyrao@...gle.com>,
	Stephen Barber <smbarber@...gle.com>
Subject: Re: [PATCH v6 0/5] zram/zsmalloc promotion

Hi Luigi,

On 08/19/2013 01:29 PM, Luigi Semenzato wrote:
> 
> We are gearing up to evaluate zswap, but we have only ported kernels
> up to 3.8 to our hardware, so we may be missing important patches.
> 
> In our experience, and with all due respect, the linux MM is a complex
> beast, and it's difficult to predict how hard it will be for us to
> switch to zswap.  Even with the relatively simple zram, our load

I think it will be easy if zswap can also create a pseudo block device(I
already done the simple implementation [PATCH 0/4] mm: merge zram into
zswap), then it's transparent for original zram users.

> triggered bugs in other parts of the MM that took a fair amount of
> work to resolve.
> 
> I may be wrong, but the in-memory compressed block device implemented
> by zram seems like a simple device which uses a well-established API
> to the rest of the kernel.  If it is removed from the kernel, will it
> be difficult for us to carry our own patch?  Because we may have to do
> that for a while.  Of course we would prefer it if it stayed in, at
> least temporarily.
> 
> Also, could someone confirm or deny that the maximum compression ratio
> in zbud is 2?  Because we easily achieve a 2.6-2.8 compression ratio
> with our loads using zram with zsmalloc and LZO or snappy.  Losing
> that memory will cause a noticeable regression, which will encourage
> us to stick with zram.
> 
> I am hoping that our load is not so unusual that we are the only Linux
> users in this situation, and that zsmalloc (or other
> allocator-compressor with similar characteristics) will continue to
> exist, whether it is used by zram or zswap.
> 
> Thanks!
> 

-- 
Regards,
-Bob
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