Re: ~500 megs cached yet 2.6.5 goes into swap hell

Lincoln Dale
2004-04-30T00:14:15Z

At 02:51 AM 30/04/2004, Andy Isaacson wrote:
>What I want is for purely sequential workloads which far exceed cache
>size (dd, updatedb, tar czf /backup/home.nightly.tar.gz /home) to avoid
>thrashing my entire desktop out of memory. I DON'T CARE if the tar
>completed in 45 minutes rather than 80. (It wouldn't, anyways, because
>it only needs about 5 MB of cache to get every bit of the speedup it was
>going to get.) But the additional latency when I un-xlock in the
>morning is annoying, and there is no benefit.
>
>For a more useful example, ideally I *should not be able to tell* that
>"dd if=/hde1 of=/hdf1" is running. [1] There is *no* benefit to cacheing
>more than about 2 pages, under this workload. But with current kernels,
>IME, that workload results in a gargantuan buffer cache and lots of
>swapout of apps I was using 3 minutes ago. I've taken to walking away
>for some coffee, coming back when it's done, and "sudo swapoff
>/dev/hda3; sudo swapon -a" to avoid the latency that is so annoying when
>trying to use bloaty apps.

the mechanism already exists; teach tar/dd and any other app that you don't
want to pollute the page-cache with data with to use O_DIRECT.

i suspect updatedb is a different case as its probably filling the system
with dcache/inode entries.

cheers,

lincoln.