This is the 7th version of adaptive read-ahead patch.
There are various code cleanups and polish ups:
- new tunable parameters: readahead_hit_rate/readahead_live_chunk
- support sparse sequential accesses
- delay look-ahead in laptop mode
- disable look-ahead for loopback file
- make mandatory thrashing protection more simple and robust
- attempt to improve responsiveness on large I/O request size
Support for sparse reads is disabled by default. One must increase
/proc/sys/vm/readahead_hit_rate to explicitly enable it. Please
refer to Documentation/sysctl/vm.txt for details.
Currently the linux kernel does not support inter-file read-ahead.
Tero Grundstr?m takes an intresting approach that achieves it: pack
a dir of small files into a loopback file with reiserfs filesystem, and
turn on sparse read support. But be prepared to waste some memory by
this way :(
For crazy laptop users who prefer aggressive read-ahead, here is the way:
# echo 10000 > /proc/sys/vm/readahead_ratio
# blockdev --setra 524280 /dev/hda # this is the max possible value
Notes:
- It is still an untested feature.
- It is safer to use blockdev+fadvise to increase ra-max for a single file,
which needs patching your movie player.
- Be sure to restore them to sane values in normal operations!
Regards,
Wu
Would you cc Nick Piggin on the radix tree patches? He has some work in
progress that may have to be synced between both of you.
On Wed, Nov 09, 2005 at 12:39:56PM -0800, Christoph Lameter wrote:
> Would you cc Nick Piggin on the radix tree patches? He has some work in
> progress that may have to be synced between both of you.
Ok, I should have cc'ed him, but thanks for your reminding anyway :)
Regards,
Wu