From: Wu Fengguang Date: Tue, 16 Jun 2009 22:31:24 +0000 (-0700) Subject: readahead: remove sync/async readahead call dependency X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=51daa88ebd8e0d437289f589af29d4b39379ea76;p=linux-beck.git 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 Signed-off-by: Wu Fengguang Cc: Ying Han Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/mm/readahead.c b/mm/readahead.c index 16378b90843e..d7c6e143a129 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); }