Re: [PATCH] Making i/dhash_entries cmdline work as it use to.

[David Howells]

Jose R. Santos <jrsantos@xxxxxxxxxxxxxx> wrote:
> Also, any particular reason why MAX_SYS_HASH_TABLE_ORDER was set to 14?
> I am already seeing the need to go higher on my 64GB setup and was 
> wondering if this could be bumped up to 19.

Yes. IBM did some testing and found that was about optimal. No significant
gain was found with anything greater.

> I'm sending a patch that get the cmdline options working as the did before
> where the could override the kernel calculations and increases 
> MAX_SYS_HASH_TABLE_ORDER to 19.  Only tested on PPC64 at the moment.

You need to be careful increasing the maximum order - you have to remember
that this affects several tables (well, at least two at the moment), and so
the effect is multiplied.

It may be reasonable to let the kernel cmdline override the maximum number of
buckets calculated on the scaling factor provided to the function (effectively
number of buckets per unit memory), but consider that the number of objects
that can be allocated and linked into the table is in effect governed by such
a factor.

David
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