RE: Limit hash table size

Chen, Kenneth W
2004-01-09T19:05:37Z

Anton Blanchard wrote:

>Have you done any analysis of hash depths of large memory machines? We
>had some extremely deep pagecache hashchains in 2.4 on a 64GB machine.
>While the radix tree should fix that, whos to say we cant get into a
>similar situation with the dcache?

We don't have any data to justify any size change for x86, that was the
main reason we limit the size by page order.

>Check out how deep some of the inode hash chains are here:
>http://www.ussg.iu.edu/hypermail/linux/kernel/0312.0/0105.html

If I read them correctly, most of the distribution is in the first 2
buckets, so it doesn't matter whether you have 100 buckets or 1 million
buckets, only first 2 are being hammered hard. So are we wasting memory
on the buckets that are not being used?

- Ken