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authorWu Fengguang <fengguang.wu@intel.com>2009-06-16 15:31:24 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-06-16 19:47:29 -0700
commit51daa88ebd8e0d437289f589af29d4b39379ea76 (patch)
treecbf2990a12ee4285d4e906c2c5614689922b8ab1 /mm/readahead.c
parent160334a0cfa8e578b718f81038026326845d07d7 (diff)
downloadlinux-51daa88ebd8e0d437289f589af29d4b39379ea76.tar.gz
readahead: remove sync/async readahead call dependency
The readahead call scheme is error-prone in that it expects the call sites to check for async readahead after doing a sync one. I.e. if (!page) page_cache_sync_readahead(); page = find_get_page(); if (page && PageReadahead(page)) page_cache_async_readahead(); This is because PG_readahead could be set by a sync readahead for the _current_ newly faulted in page, and the readahead code simply expects one more callback on the same page to start the async readahead. If the caller fails to do so, it will miss the PG_readahead bits and never able to start an async readahead. Eliminate this insane constraint by piggy-backing the async part into the current readahead window. Now if an async readahead should be started immediately after a sync one, the readahead logic itself will do it. So the following code becomes valid: (the 'else' in particular) if (!page) page_cache_sync_readahead(); else if (PageReadahead(page)) page_cache_async_readahead(); Cc: Nick Piggin <npiggin@suse.de> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com> Cc: Ying Han <yinghan@google.com> 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.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/mm/readahead.c b/mm/readahead.c
index 16378b90843..d7c6e143a12 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -421,6 +421,16 @@ ondemand_readahead(struct address_space *mapping,
ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;
readit:
+ /*
+ * Will this read hit the readahead marker made by itself?
+ * If so, trigger the readahead marker hit now, and merge
+ * the resulted next readahead window into the current one.
+ */
+ if (offset == ra->start && ra->size == ra->async_size) {
+ ra->async_size = get_next_ra_size(ra, max);
+ ra->size += ra->async_size;
+ }
+
return ra_submit(ra, mapping, filp);
}