Re: Reducing inode cache usage on 2.4?

[Marcelo Tosatti <marcelo.tosatti@cyclades.com>]

On Mon, Dec 20, 2004 at 06:54:09PM +0100, Andrea Arcangeli wrote:
> On Mon, Dec 20, 2004 at 01:06:34PM -0200, Marcelo Tosatti wrote:
> > The thing is right now we dont try to reclaim from icache/dcache _at all_ 
> > if enough clean pagecache pages are found and reclaimed.
> > 
> > Its sounds unfair to me.
> 
> If most ram is in pagecache there's not much point to shrink the dcache.
> The more ram goes into dcache/icache, the less ram will be in pagecache,
> and the more likely we'll start shrinking dcache/icache. Also keep in
> mind in a highmem machine the pagecache will be in highmemory and the
> dcache/icache in lowmemory (on very very big boxes the lowmem_reserve
> algorithm pratically splits the two in non-overkapping zones), so
> especially on a big highmem machine shrinking dcache/icache during a
> pagecache allocation (because this is what the workload is doing: only
> pagecache allocations) is a worthless effort.
> 
> This is the best solution we have right now, but there have been several
> discussions in the past on how to shrink dcache/icache. But if we want
> to talk on how to change this, we should talk about 2.6/2.7 only IMHO.
> 
> > Why not? If we have a lot of them they will probably be hurting performace, which seems
> > to be the case now.
> 
> The slowdown could be because the icache/dcache hash size is too small.
> It signals collisions in the dcache/icache hashtable. 2.6 with bootmem
> allocated hashes should be better. Optimizing 2.4 for performance if not
> worth the risk IMHO. I would suggest to check if you can reproduce in
> 2.6, and fix it there, if it's still there.
> 
> > Following this logic any workload which generates pagecache and happen
> > to, most times, have enough pagecache clean to be reclaimed should not
> > reclaim the i/dcache's.  Which is not right.
> 
> This mostly happens for cache-polluting-workloads like in this testcase.
> If the cache would be activated, there would be less pages in the
> inactive list and you had a better chance to invoke the dcache/icache
> shrinking.

OK I buy your arguments I'll revert Andrew's patch.