From 045a2529a3513faed2d45bd82f9013b124309d94 Mon Sep 17 00:00:00 2001 From: Wu Fengguang Date: Tue, 16 Jun 2009 15:31:33 -0700 Subject: readahead: move the random read case to bottom Split all readahead cases, and move the random one to bottom. No behavior changes. This is to prepare for the introduction of context readahead, and make it easy for inserting accounting/tracing points for each case. Signed-off-by: Wu Fengguang Cc: Vladislav Bolkhovitin Cc: Jens Axboe Cc: Jeff Moyer Cc: Nick Piggin Cc: Ying Han Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/readahead.c | 46 +++++++++++++++++++++++++--------------------- 1 file changed, 25 insertions(+), 21 deletions(-) (limited to 'mm/readahead.c') diff --git a/mm/readahead.c b/mm/readahead.c index a7f01fcce9e7..ceed7e4790bd 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -339,33 +339,25 @@ ondemand_readahead(struct address_space *mapping, unsigned long req_size) { unsigned long max = max_sane_readahead(ra->ra_pages); - pgoff_t prev_offset; - int sequential; + + /* + * start of file + */ + if (!offset) + goto initial_readahead; /* * It's the expected callback offset, assume sequential access. * Ramp up sizes, and push forward the readahead window. */ - if (offset && (offset == (ra->start + ra->size - ra->async_size) || - offset == (ra->start + ra->size))) { + if ((offset == (ra->start + ra->size - ra->async_size) || + offset == (ra->start + ra->size))) { ra->start += ra->size; ra->size = get_next_ra_size(ra, max); ra->async_size = ra->size; goto readit; } - prev_offset = ra->prev_pos >> PAGE_CACHE_SHIFT; - sequential = offset - prev_offset <= 1UL || req_size > max; - - /* - * Standalone, small read. - * Read as is, and do not pollute the readahead state. - */ - if (!hit_readahead_marker && !sequential) { - return __do_page_cache_readahead(mapping, filp, - offset, req_size, 0); - } - /* * Hit a marked page without valid readahead state. * E.g. interleaved reads. @@ -391,12 +383,24 @@ ondemand_readahead(struct address_space *mapping, } /* - * It may be one of - * - first read on start of file - * - sequential cache miss - * - oversize random read - * Start readahead for it. + * oversize read */ + if (req_size > max) + goto initial_readahead; + + /* + * sequential cache miss + */ + if (offset - (ra->prev_pos >> PAGE_CACHE_SHIFT) <= 1UL) + goto initial_readahead; + + /* + * standalone, small random read + * Read as is, and do not pollute the readahead state. + */ + return __do_page_cache_readahead(mapping, filp, offset, req_size, 0); + +initial_readahead: ra->start = offset; ra->size = get_init_ra_size(req_size, max); ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size; -- cgit v1.2.1