linux-kernel - Re: [PATCH 07/10] Increase compressed page size threshold

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Date:	Mon, 9 Aug 2010 21:32:11 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Nitin Gupta <ngupta@...are.org>
Cc:	Pekka Enberg <penberg@...helsinki.fi>,
	Minchan Kim <minchan.kim@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <greg@...ah.com>,
	Linux Driver Project <devel@...uxdriverproject.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 07/10] Increase compressed page size threshold

Hi Nitin,

On Mon, Aug 9, 2010 at 8:26 PM, Nitin Gupta <ngupta@...are.org> wrote:
> Compression takes much more time than decompression. So, its quite
> wasteful in terms of both CPU cycles and memory usage to have a very
> low compressed page size threshold and thereby storing such not-so-well
> compressible pages as-is (uncompressed). So, increasing it from
> PAGE_SIZE/2 to PAGE_SIZE/8*7. A low threshold was useful when we had
> "backing swap" support where we could forward such pages to the backing
> device (applicable only when zram was used as swap disk).
>
> It is not yet configurable through sysfs but may be exported in future,
> along with threshold for average compression ratio.
>
> Signed-off-by: Nitin Gupta <ngupta@...are.org>

The description makes sense but lacks any real data. What kind of
workloads did you test this with? Where does it help most? How much?

                        Pekka
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