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

["Brett E." <brettspamacct@fastclick.com>]

Jeff Garzik wrote:

> 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

Or how about "Use ALL the cache you want Mr. Kernel.  But when I want 
more physical memory pages, just reap cache pages and only swap out when 
the cache is down to a certain size(configurable, say 100megs or 
something)."