On Sun, Apr 26, 2009 at 11:51:22PM +0200, Michael Monnerie wrote:
> On Samstag 25 April 2009 Eric Sandeen wrote:
> > *from Documentation/sysctl/vm.txt:
> > vfs_cache_pressure
> > ------------------
> > Controls the tendency of the kernel to reclaim the memory which is
> > used for caching of directory and inode objects.
> > At the default value of vfs_cache_pressure=100 the kernel will
> > attempt to reclaim dentries and inodes at a "fair" rate with respect
> > to pagecache and swapcache reclaim. Decreasing vfs_cache_pressure
> > causes the kernel to prefer to retain dentry and inode caches.
> > Increasing vfs_cache_pressure beyond 100 causes the kernel to prefer
> > to reclaim dentries and inodes.
> So if I decrease it, lets say to 60, Linux prefers to remember
> files/dirs over their content. An increase to 150 would mean Linux
> prefers to keep file contents over dirs/files?
Yep, that's right.
> If so, I think for a fileserver for many users accessing many
> dirs/files, I'd prefer a lower value, in order to prevent searching.
> Disk contents can be read fast, with all the read-ahead caching of
> disks/controllers and Linux itself, but the scattered dirs take loooong
> to scan sometimes. (Example: a foto collection with 50.000 files in many
> dirs). Am I right?
Approximate answer is: it depends on the frequency of meta-data reads vs.
data reads. Your reasoning is fine if whoever access the photo collection
does not frequently read the photos themselves.
Best answer is: benchmark it with the exact workload you have to deal with
Josef 'Jeff' Sipek.
Intellectuals solve problems; geniuses prevent them
- Albert Einstein