From: Fengguang Wu - keep lookahead_index if the current chunk is lost, so that when we revisted this stream, the state based method see a consistent state. - correct the thrashing-threshold computation - discount read-ahead size more, to free more memory to the system on pressure - disable look-ahead when thrashed, just to be safe Signed-off-by: Fengguang Wu Signed-off-by: Andrew Morton --- mm/readahead.c | 28 +++++++++++++--------------- 1 files changed, 13 insertions(+), 15 deletions(-) diff -puN mm/readahead.c~readahead-thrashing-recovery-method-fix mm/readahead.c --- a/mm/readahead.c~readahead-thrashing-recovery-method-fix +++ a/mm/readahead.c @@ -1530,28 +1530,26 @@ thrashing_recovery_readahead(struct addr ra->readahead_index - offset); #endif - /* - * Some thrashing occur in (ra_index, la_index], in which case the - * old read-ahead chunk is lost soon after the new one is allocated. - * Ensure that we recover all needed pages in the old chunk. - */ - if (offset < ra->ra_index) - ra_size = ra->ra_index - offset; - else { + if (offset < ra->ra_index) { + /* + * Thrashed when we are in [la_index, ra_index), i.e. + * the old chunk is lost soon after the new one is allocated. + * Ensure that we recover all needed pages in the old chunk. + * And futher keep the lookahead_index untouched. + */ + ra_size = ra->lookahead_index - offset; + } else { /* After thrashing, we know the exact thrashing-threshold. */ - ra_size = offset - ra->ra_index; + ra_size = offset - ra->la_index; update_ra_thrash_bytes(mapping->backing_dev_info, ra_size); - /* And we'd better be a bit conservative. */ - ra_size = ra_size * 3 / 4; + /* And be cooperative: the system may be hunting for memory. */ + ra_size = MIN_RA_PAGES + ra_size / 2; } - if (ra_size > ra_max) - ra_size = ra_max; - ra_set_class(ra, RA_CLASS_THRASHING); ra_set_index(ra, offset, offset); - ra_set_size(ra, ra_size, ra_size / LOOKAHEAD_RATIO); + ra_set_size(ra, ra_size, 0); return ra_submit(ra, mapping, filp); } _