linux-kernel - Re: [PATCH v4 0/8] staging: zcache: Support zero-filled pages more efficiently

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Date:	Wed, 20 Mar 2013 07:34:02 +0800
From:	Ric Mason <ric.masonn@...il.com>
To:	Wanpeng Li <liwanp@...ux.vnet.ibm.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Konrad Rzeszutek Wilk <konrad@...nok.org>,
	Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/8] staging: zcache: Support zero-filled pages more
 efficiently

On 03/19/2013 05:25 PM, Wanpeng Li wrote:
> Hi Greg,
>
> Since you have already merge 1/8, feel free to merge 2/8~8/8, I have already
> rebased against staging-next.
>
> Changelog:
>   v3 -> v4:
>    * handle duplication in page_is_zero_filled, spotted by Bob
>    * fix zcache writeback in dubugfs
>    * fix pers_pageframes|_max isn't exported in debugfs
>    * fix static variable defined in debug.h but used in multiple C files
>    * rebase on Greg's staging-next
>   v2 -> v3:
>    * increment/decrement zcache_[eph|pers]_zpages for zero-filled pages, spotted by Dan
>    * replace "zero" or "zero page" by "zero_filled_page", spotted by Dan
>   v1 -> v2:
>    * avoid changing tmem.[ch] entirely, spotted by Dan.
>    * don't accumulate [eph|pers]pageframe and [eph|pers]zpages for
>      zero-filled pages, spotted by Dan
>    * cleanup TODO list
>    * add Dan Acked-by.
>
> Motivation:
>
> - Seth Jennings points out compress zero-filled pages with LZO(a lossless
>    data compression algorithm) will waste memory and result in fragmentation.
>    https://lkml.org/lkml/2012/8/14/347
> - Dan Magenheimer add "Support zero-filled pages more efficiently" feature
>    in zcache TODO list https://lkml.org/lkml/2013/2/13/503
>
> Design:
>
> - For store page, capture zero-filled pages(evicted clean page cache pages and
>    swap pages), but don't compress them, set pampd which store zpage address to
>    0x2(since 0x0 and 0x1 has already been ocuppied) to mark special zero-filled
>    case and take advantage of tmem infrastructure to transform handle-tuple(pool
>    id, object id, and an index) to a pampd. Twice compress zero-filled pages will
>    contribute to one zcache_[eph|pers]_pageframes count accumulated.
> - For load page, traverse tmem hierachical to transform handle-tuple to pampd
>    and identify zero-filled case by pampd equal to 0x2 when filesystem reads
>    file pages or a page needs to be swapped in, then refill the page to zero
>    and return.
>
> Test:
>
> dd if=/dev/zero of=zerofile bs=1MB count=500
> vmtouch -t zerofile
> vmtouch -e zerofile
>
> formula:
> - fragmentation level = (zcache_[eph|pers]_pageframes * PAGE_SIZE - zcache_[eph|pers]_zbytes)
>    * 100 / (zcache_[eph|pers]_pageframes * PAGE_SIZE)
> - memory zcache occupy = zcache_[eph|pers]_zbytes
>
> Result:
>
> without zero-filled awareness:
> - fragmentation level: 98%
> - memory zcache occupy: 238MB
> with zero-filled awareness:
> - fragmentation level: 0%
> - memory zcache occupy: 0MB
>
> Wanpeng Li (8):
>    introduce zero filled pages handler
>    zero-filled pages awareness
>    handle zcache_[eph|pers]_pages for zero-filled page
>    fix pers_pageframes|_max aren't exported in debugfs
>    fix zcache writeback in debugfs
>    fix static variables are defined in debug.h but use in multiple C files
>    introduce zero-filled page stat count
>    clean TODO list

You can add Reviewed-by: Ric Mason <ric.masonn@...il.com> to this patchset.

>
>   drivers/staging/zcache/TODO          |    3 +-
>   drivers/staging/zcache/debug.c       |    5 +-
>   drivers/staging/zcache/debug.h       |   77 +++++++++++++---------
>   drivers/staging/zcache/zcache-main.c |  147 ++++++++++++++++++++++++++++++----
>   4 files changed, 185 insertions(+), 47 deletions(-)
>

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