From: Wu Fengguang backing_dev_info.ra_thrash_bytes is dynamicly updated to be a little above the thrashing safe read-ahead size. It is used in the initial method where the thrashing threshold for the particular reader is still unknown. Signed-off-by: Wu Fengguang Signed-off-by: Andrew Morton --- mm/readahead.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff -puN mm/readahead.c~readahead-initial-method-thrashing-guard-size mm/readahead.c --- devel/mm/readahead.c~readahead-initial-method-thrashing-guard-size 2006-06-09 01:22:48.000000000 -0700 +++ devel-akpm/mm/readahead.c 2006-06-09 01:22:48.000000000 -0700 @@ -799,6 +799,22 @@ out: } /* + * Update `backing_dev_info.ra_thrash_bytes' to be a _biased_ average of + * read-ahead sizes. Which makes it an a-bit-risky(*) estimation of the + * _minimal_ read-ahead thrashing threshold on the device. + * + * (*) Note that being a bit risky can _help_ overall performance. + */ +static inline void update_ra_thrash_bytes(struct backing_dev_info *bdi, + unsigned long ra_size) +{ + ra_size <<= PAGE_CACHE_SHIFT; + bdi->ra_thrash_bytes = (bdi->ra_thrash_bytes < ra_size) ? + (ra_size + bdi->ra_thrash_bytes * 1023) / 1024: + (ra_size + bdi->ra_thrash_bytes * 7) / 8; +} + +/* * The node's accumulated aging activities. */ static unsigned long node_readahead_aging(void) @@ -1153,6 +1169,10 @@ state_based_readahead(struct address_spa limit_rala(growth_limit, la_old, &ra_size, &la_size); + /* ra_size in its _steady_ state reflects thrashing threshold */ + if (page && ra_old + ra_old / 8 >= ra_size) + update_ra_thrash_bytes(mapping->backing_dev_info, ra_size); + ra_set_class(ra, RA_CLASS_STATE); ra_set_index(ra, index, ra->readahead_index); ra_set_size(ra, ra_size, la_size); _