From: Steven Pratt The current current get_init_ra_size is not optimal across different IO sizes and max_readahead values. Here is a quick summary of sizes computed under current design and under the attached patch. All of these assume 1st IO at offset 0, or 1st detected sequential IO. 32k max, 4k request old new ----------------- 8k 8k 16k 16k 32k 32k 128k max, 4k request old new ----------------- 32k 16k 64k 32k 128k 64k 128k 128k 128k max, 32k request old new ----------------- 32k 64k <----- 64k 128k 128k 128k 512k max, 4k request old new ----------------- 4k 32k <---- 16k 64k 64k 128k 128k 256k 512k 512k Cc: Oleg Nesterov Cc: Steven Pratt Cc: Ram Pai Cc: Trond Myklebust Signed-off-by: Andrew Morton --- mm/readahead.c | 6 +++--- 1 files changed, 3 insertions(+), 3 deletions(-) diff -puN mm/readahead.c~readahead-fix-initial-window-size-calculation mm/readahead.c --- devel/mm/readahead.c~readahead-fix-initial-window-size-calculation 2006-02-27 17:23:58.000000000 -0800 +++ devel-akpm/mm/readahead.c 2006-02-27 17:23:58.000000000 -0800 @@ -83,10 +83,10 @@ static unsigned long get_init_ra_size(un { unsigned long newsize = roundup_pow_of_two(size); - if (newsize <= max / 64) - newsize = newsize * newsize; + if (newsize <= max / 32) + newsize = newsize * 4; else if (newsize <= max / 4) - newsize = max / 4; + newsize = newsize * 2; else newsize = max; return newsize; _