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SubjectRe: [PATCH part2 v6 0/3] staging: zcache: Support zero-filled pages more efficiently
cc Bob
On 04/07/2013 05:03 PM, Wanpeng Li wrote:
> On Wed, Apr 03, 2013 at 06:16:20PM +0800, Wanpeng Li wrote:
>> Changelog:
>> v5 -> v6:
>> * shove variables in debug.c and in debug.h just have an extern, spotted by Konrad
>> * update patch description, spotted by Konrad
>> v4 -> v5:
>> * fix compile error, reported by Fengguang, Geert
>> * add check for !is_ephemeral(pool), spotted by Bob
>> 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.
>>
> Hi Dan,
>
> Some issues against Ramster:
>
> - Ramster who takes advantage of zcache also should support zero-filled
> pages more efficiently, correct? It doesn't handle zero-filled pages well
> currently.
> - Ramster DebugFS counters are exported in /sys/kernel/mm/, but zcache/frontswap/cleancache
> all are exported in /sys/kernel/debug/, should we unify them?
> - If ramster also should move DebugFS counters to a single file like
> zcache do?
>
> If you confirm these issues are make sense to fix, I will start coding. ;-)
>
> Regards,
> Wanpeng Li
>
>> 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 (3):
>> staging: zcache: fix static variables defined in debug.h but used in
>> mutiple C files
>> staging: zcache: introduce zero-filled page stat count
>> staging: zcache: clean TODO list
>>
>> drivers/staging/zcache/TODO | 3 +-
>> drivers/staging/zcache/debug.c | 35 +++++++++++++++
>> drivers/staging/zcache/debug.h | 79 ++++++++++++++++++++-------------
>> drivers/staging/zcache/zcache-main.c | 4 ++
>> 4 files changed, 88 insertions(+), 33 deletions(-)
>>
>> --
>> 1.7.5.4
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