- cancel look-ahead if readahead size is small compared to the look-ahead size, to avoid too small I/O size, and not to add more memory/io pressure on the possibly loaded system. - prevent issuing tiny readahead size, by applying a minimal limit Signed-off-by: Fengguang Wu --- mm/readahead.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-) --- linux-2.6.20-rc4-mm1.orig/mm/readahead.c +++ linux-2.6.20-rc4-mm1/mm/readahead.c @@ -932,17 +932,21 @@ static int adjust_rala(unsigned long ra_ unsigned long *ra_size, unsigned long *la_size) { /* - * Substract the old look-ahead to get real safe size for the next - * read-ahead request. + * Cancel asynchrous read-ahead, + * if there is a major upsurge of load, or fall of this stream's speed. */ - if (*ra_size > *la_size) - *ra_size -= *la_size; - else { + if (*ra_size <= *la_size * 2) { ra_account(NULL, RA_EVENT_READAHEAD_SHRINK, *ra_size); return 0; } /* + * Substract the old look-ahead to get real safe size for the next + * read-ahead request. + */ + *ra_size -= *la_size; + + /* * Set new la_size according to the (still large) ra_size. */ *la_size = *ra_size / LOOKAHEAD_RATIO; @@ -956,6 +960,13 @@ static void limit_rala(unsigned long ra_ unsigned long stream_shift; /* + * Protect against too small I/O sizes, + * by mapping [0, 4*min] to [min, 4*min]. + */ + if (*ra_size < 4 * MIN_RA_PAGES) + *ra_size = MIN_RA_PAGES + *ra_size * 3 / 4; + + /* * Apply basic upper limits. */ if (*ra_size > ra_max) -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/