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authorJan Kara <jack@suse.cz>2007-05-06 14:49:25 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-05-07 12:12:52 -0700
commitec0f16372277052a29a6c17527c6cae5e898b3fd (patch)
tree35636edac6ed01baf301f3aca96f090caae82c9d /mm/readahead.c
parentb813e931b4c8235bb42e301096ea97dbdee3e8fe (diff)
downloadlwn-ec0f16372277052a29a6c17527c6cae5e898b3fd.tar.gz
lwn-ec0f16372277052a29a6c17527c6cae5e898b3fd.zip
readahead: improve heuristic detecting sequential reads
Introduce ra.offset and store in it an offset where the previous read ended. This way we can detect whether reads are really sequential (and thus we should not mark the page as accessed repeatedly) or whether they are random and just happen to be in the same page (and the page should really be marked accessed again). Signed-off-by: Jan Kara <jack@suse.cz> Acked-by: Nick Piggin <nickpiggin@yahoo.com.au> Cc: WU Fengguang <wfg@mail.ustc.edu.cn> 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.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/mm/readahead.c b/mm/readahead.c
index 93d9ee692fd8..0a6fed9d365c 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -207,6 +207,8 @@ out:
* If page_cache_readahead sees that it is again being called for
* a page which it just looked at, it can return immediately without
* making any state changes.
+ * offset: Offset in the prev_page where the last read ended - used for
+ * detection of sequential file reading.
* ahead_start,
* ahead_size: Together, these form the "ahead window".
* ra_pages: The externally controlled max readahead for this fd.
@@ -473,6 +475,7 @@ page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra,
/* Note that prev_page == -1 if it is a first read */
sequential = (offset == ra->prev_page + 1);
ra->prev_page = offset;
+ ra->offset = 0;
max = get_max_readahead(ra);
newsize = min(req_size, max);