On Fri, Sep 10, 2010 at 06:02:48PM +0200, Johannes Stezenbach wrote: > > Linear read heuristic might be a good guess, but it would > be nice to hear a comment from a vm/fs expert which > confirms this works as intended. Apparently I'm unworthy to get a response from someone knowledgable :-( Anyway I found lmdd (from lmbench) can do random reads, and indeed causes the data to enter the block (page?) cache, replacing the previous data. Johannes zzz:~# echo 3 >/proc/sys/vm/drop_caches zzz:~# ./lmdd if=~js/qemu/test.img bs=1M count=1000 1000.0000 MB in 17.7554 secs, 56.3210 MB/sec zzz:~# ./lmdd if=~js/qemu/test.img bs=1M count=1000 1000.0000 MB in 0.9112 secs, 1097.4178 MB/sec zzz:~# ./lmdd if=~js/qemu/test2.img bs=1M count=1000 rand=1G norepeat= norepeat on 238035072 norepeat on 724579648 1000.0000 MB in 21.4419 secs, 46.6376 MB/sec zzz:~# ./lmdd if=~js/qemu/test2.img bs=1M count=1000 rand=1G norepeat= norepeat on 238035072 norepeat on 724579648 1000.0000 MB in 14.3859 secs, 69.5125 MB/sec zzz:~# ./lmdd if=~js/qemu/test2.img bs=1M count=1000 rand=1G norepeat= norepeat on 238035072 norepeat on 724579648 1000.0000 MB in 0.8764 secs, 1141.0810 MB/sec -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>