diff options
| author | Fengguang Wu <wfg@mail.ustc.edu.cn> | 2007-07-19 01:48:07 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2007-07-19 10:04:44 -0700 |
| commit | fe3cba17c49471e99d3421e675fc8b3deaaf0b70 (patch) | |
| tree | df696c4584c6db2e439f068d2474fcb946ca587d /mm/readahead.c | |
| parent | d8983910a4045fa21022cfccf76ed13eb40fd7f5 (diff) | |
| download | linux-fe3cba17c49471e99d3421e675fc8b3deaaf0b70.tar.bz2 | |
mm: share PG_readahead and PG_reclaim
Share the same page flag bit for PG_readahead and PG_reclaim.
One is used only on file reads, another is only for emergency writes. One
is used mostly for fresh/young pages, another is for old pages.
Combinations of possible interactions are:
a) clear PG_reclaim => implicit clear of PG_readahead
it will delay an asynchronous readahead into a synchronous one
it actually does _good_ for readahead:
the pages will be reclaimed soon, it's readahead thrashing!
in this case, synchronous readahead makes more sense.
b) clear PG_readahead => implicit clear of PG_reclaim
one(and only one) page will not be reclaimed in time
it can be avoided by checking PageWriteback(page) in readahead first
c) set PG_reclaim => implicit set of PG_readahead
will confuse readahead and make it restart the size rampup process
it's a trivial problem, and can mostly be avoided by checking
PageWriteback(page) first in readahead
d) set PG_readahead => implicit set of PG_reclaim
PG_readahead will never be set on already cached pages.
PG_reclaim will always be cleared on dirtying a page.
so not a problem.
In summary,
a) we get better behavior
b,d) possible interactions can be avoided
c) racy condition exists that might affect readahead, but the chance
is _really_ low, and the hurt on readahead is trivial.
Compound pages also use PG_reclaim, but for now they do not interact with
reclaim/readahead code.
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/readahead.c')
| -rw-r--r-- | mm/readahead.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/mm/readahead.c b/mm/readahead.c index 5b3c9b7d70fa..205a4a431516 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -448,6 +448,12 @@ page_cache_readahead_ondemand(struct address_space *mapping, return 0; if (page) { + /* + * It can be PG_reclaim. + */ + if (PageWriteback(page)) + return 0; + ClearPageReadahead(page); /* |