Re: Reducing inode cache usage on 2.4?

From: Andrea Arcangeli
Date: Mon Dec 20 2004 - 10:25:00 EST

On Mon, Dec 20, 2004 at 10:46:04AM -0200, Marcelo Tosatti wrote:
> On Mon, Dec 20, 2004 at 01:47:46PM +0000, James Pearson wrote:
> > I've tested the patch on my test setup - running a 'find $disk -type f'
> > and a cat of large files to /dev/null at the same time does indeed
> > reduce the size of the inode and dentry caches considerably - the first
> > column numbers for fs_inode, linvfs_icache and dentry_cache in
> > /proc/slabinfo hover at about 400-600 (over 900000 previously).
> >
> > However, is this going a bit to far the other way? When I boot the
> > machine with 4Gb RAM, the inode and dentry caches are squeezed to the
> > same amounts, but it may be the case that it would be more beneficial to
> > have more in the inode and dentry caches? i.e. I guess some sort of
> > tunable factor that limits the minimum size of the inode and dentry
> > caches in this case?
> One can increase vm_vfs_scan_ratio if required, but hopefully this change
> will benefit all workloads.
> Andrew, Andrea, do you think of any workloads which might be hurt by this change?

I wouldn't touch the defaults, but the sysctl is there so if you've a
strange workload you can tune for it.

There's nothing wrong with dcache/icache growing a lot. A cat of a large
file is polluting the cache, so that's not a workload that should shrink
the dcache/icache. I'd prefer a feedback based on a real useful workload
before even considering touching the defaults at this time.
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