[LU-16338] read-ahead more than file size for a small file

Related — Tue, 25 Apr 2023 03:46:12 +0000

The following scripts will read pages more than file size:

test_907()
{
        local file=$DIR/$tfile

        $LCTL set_param -n llite.*.read_ahead_stats=0
        fallocate -l 16K $file || error "failed to fallocate $file"
        cancel_lru_locks osc
        #dd if=$file of=/dev/null bs=1M
        $MULTIOP $file or1048576c
        $LCTL get_param llite.*.read_ahead_stats
}
run_test 907 "read ahaed for small file"

The readahead page stats are as follows:

== sanity test 907: read ahaed for small file ============ 04:38:01 (1669196281)
short read: 16384/1048576
short read: 0/1032192
llite.lustre-ffff938b7849d000.read_ahead_stats=
snapshot_time             4011.320890492 secs.nsecs
start_time                0.000000000 secs.nsecs
elapsed_time              4011.320890492 secs.nsecs
hits                      4 samples [pages]
misses                    1 samples [pages]
zero_size_window          4 samples [pages]
failed_to_reach_end       1 samples [pages]
failed_to_fast_read       1 samples [pages]
readahead_pages           1 samples [pages] 255 255 255

For small files, the read-ahead pages reach 255, it is not reasonable...

Whamcloud Community JIRA

[LU-16338] read-ahead more than file size for a small file