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

Jeff Garzik
2004-04-29T00:10:31Z

Andrew Morton wrote:
> Swapout is good. It frees up unused memory. I run my desktop machines at
> swappiness=100.

The definition of "unused" is quite subjective and app-dependent...

I've see reports with increasing frequency about the swappiness of the
2.6.x kernels, from people who were already annoyed at the swappiness of
2.4.x kernels :)

Favorite pathological (and quite common) examples are the various 4am
cron jobs that scan your entire filesystem. Running that process
overnight on a quiet machines practically guarantees a huge burst of
disk activity, with unwanted results:
1) Inode and page caches are blown away
2) A lot of your desktop apps are swapped out

Additionally, a (IMO valid) maxim of sysadmins has been "a properly
configured server doesn't swap". There should be no reason why this
maxim becomes invalid over time. When Linux starts to swap out apps the
sysadmin knows will be useful in an hour, or six hours, or a day just
because it needs a bit more file cache, I get worried.

There IMO should be some way to balance the amount of anon-vma's such
that the sysadmin can say "stop taking 70% of my box's memory for
disposable cache, use it instead for apps you would otherwise swap out,
you memory-hungry kernel you."

Jeff