Re: memory usage

[Samuel Thibault <samuel.thibault@ens-lyon.org>]

Hi,

Samuel Thibault, le Mon 06 Aug 2007 21:10:02 +0200, a écrit :
> Also, something odd: say I have a big file /tmp/foo
> 
> $ cat /tmp/foo > /dev/null
> ... "inactive" grows in vmstat, takes some time...
> $ cat /tmp/foo > /dev/null
> takes almost no time since it's all cached.
> $ find /var -printf ""
> ... "inactive" falls down to the original value
> $ cat /tmp/foo > /dev/null
> ... "inactive" grows in vmstat again, takes some time...
> 
> It looks like resolving directories/files entries somehow flushes out
> the page cache.  There actually doesn't seem to be any caching for
> directories/files: find /var/log always reads from the disk (the led
> flashes).

I've found the "problem": vm/vm_object.c:171: 
int             vm_object_cached_max = 200;    /* may be patched*/

Only 200 objects at a time may be held in memory. By nowadays'
standards, that seems quite low. In the case I've raised (find /var),
it's just not enough (the result can't fit into 200 objects).  We should
probably raise it in debian at least.

Samuel