Messages in this thread | | | Date | Mon, 20 Dec 2004 18:54:09 +0100 | From | Andrea Arcangeli <> | Subject | Re: Reducing inode cache usage on 2.4? |
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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. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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