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SubjectRe: [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@gmail.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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