Changelog:
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.
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):
staging: zcache: Support zero-filled pages more efficiently
staging: zcache: zero-filled pages awareness
staging: zcache: handle zcache_[eph|pers]_zpages for zero-filled page
staging: zcache: fix pers_pageframes|_max aren't exported in debugfs
staging: zcache: fix zcache writeback in debugfs
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 | 5 +-
drivers/staging/zcache/debug.h | 77 +++++++++++--------
drivers/staging/zcache/zcache-main.c | 141 ++++++++++++++++++++++++++++++++--
4 files changed, 183 insertions(+), 43 deletions(-)
--
1.7.7.6
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