[PATCH 4/9] readahead: quick startup on sequential mmap readahead

[Fengguang Wu <wfg@mail.ustc.edu.cn>]

When the user explicitly sets MADV_SEQUENTIAL, we should really avoid the slow
readahead size ramp-up phase and start full-size readahead immediately.

This patch won't change behavior for the auto-detected sequential mmap reads.
Its previous read-around size is ra_pages/2, so it will be doubled to the full
readahead size anyway.

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---
 mm/filemap.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- linux-2.6.24-rc4-mm1.orig/mm/filemap.c
+++ linux-2.6.24-rc4-mm1/mm/filemap.c
@@ -1320,7 +1320,7 @@ static void do_sync_mmap_readahead(struc
 
 	if (VM_SequentialReadHint(vma) ||
 			offset - 1 == (ra->prev_pos >> PAGE_CACHE_SHIFT)) {
-		page_cache_sync_readahead(mapping, ra, file, offset, 1);
+		page_cache_sync_readahead(mapping, ra, file, offset, ra->ra_pages);
 		return;
 	}
 

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