linux-kernel - RE: [PATCH 0/4] mm: zpool: add common api for zswap to use zbud/zsmalloc

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Date:	Mon, 21 Apr 2014 10:47:16 +0800
From:	Weijie Yang <weijie.yang@...sung.com>
To:	'Dan Streetman' <ddstreet@...e.org>,
	'Seth Jennings' <sjennings@...iantweb.net>,
	'Minchan Kim' <minchan@...nel.org>,
	'Nitin Gupta' <ngupta@...are.org>
Cc:	'Andrew Morton' <akpm@...ux-foundation.org>,
	'Bob Liu' <bob.liu@...cle.com>,
	'Hugh Dickins' <hughd@...gle.com>,
	'Mel Gorman' <mgorman@...e.de>,
	'Rik van Riel' <riel@...hat.com>,
	'Johannes Weiner' <hannes@...xchg.org>,
	'Sergey Senozhatsky' <sergey.senozhatsky@...il.com>,
	'Linux-MM' <linux-mm@...ck.org>,
	'linux-kernel' <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 0/4] mm: zpool: add common api for zswap to use
 zbud/zsmalloc



On Sat, Apr 19, 2014 at 11:52 PM, Dan Streetman <ddstreet@...e.org> wrote:
> In order to allow zswap users to choose between zbud and zsmalloc for
> the compressed storage pool, this patch set adds a new api "zpool" that
> provides an interface to both zbud and zsmalloc.  Only a minor change
> to zbud's interface was needed, as detailed in the first patch;
> zsmalloc required shrinking to be added and a minor interface change,
> as detailed in the second patch.
> 
> I believe Seth originally was using zsmalloc for swap, but there were
> concerns about how significant the impact of shrinking zsmalloc would
> be when zswap had to start reclaiming pages.  That still may be an
> issue, but this at least allows users to choose themselves whether
> they want a lower-density or higher-density compressed storage medium.
> At least for situations where zswap reclaim is never or rarely reached,
> it probably makes sense to use the higher density of zsmalloc.
> 
> Note this patch series does not change zram to use zpool, although that
> change should be possible as well.

I think this idea is acceptable, because for embedded devices reclaiming is
risky due to its write lifetime. By using zsmalloc, zswap user can not only take
the benefit of higher-density compressed storage but aslo supporting the
GFP_HIGHMEM in 32bit system.

I will pay attention to this patch set and give my opinion after my review.

Thanks for your work

> 
> Dan Streetman (4):
>   mm: zpool: zbud_alloc() minor param change
>   mm: zpool: implement zsmalloc shrinking
>   mm: zpool: implement common zpool api to zbud/zsmalloc
>   mm: zpool: update zswap to use zpool
> 
>  drivers/block/zram/zram_drv.c |   2 +-
>  include/linux/zbud.h          |   3 +-
>  include/linux/zpool.h         | 166 ++++++++++++++++++
>  include/linux/zsmalloc.h      |   7 +-
>  mm/Kconfig                    |  43 +++--
>  mm/Makefile                   |   1 +
>  mm/zbud.c                     |  28 ++--
>  mm/zpool.c                    | 380 ++++++++++++++++++++++++++++++++++++++++++
>  mm/zsmalloc.c                 | 168 +++++++++++++++++--
>  mm/zswap.c                    |  70 ++++----
>  10 files changed, 787 insertions(+), 81 deletions(-)
>  create mode 100644 include/linux/zpool.h
>  create mode 100644 mm/zpool.c
> 
> --
> 1.8.3.1

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