Re: [PATCH] knfsd: allocate readahead cache in individual chunks

[Trond Myklebust <trond.myklebust@fys.uio.no>]

On Thu, 2008-08-14 at 14:52 -0400, Jeff Layton wrote:
> 1) do what I did here (individual kmalloc for each raparm)
> 
> 2) do an allocation of an raparms array for each hash bucket, but when
> we get to larger thread counts, these will still require multi-page
> allocations:
> 
> 8192 threads * 2 / 16 buckets * 72 bytes = 73728 byte allocation
> 
> 3) declare a separate slabcache for this and allocate each raparm
> individually from that
> 
> ...#3 might be reasonable, but we could end up wasting even more memory
> that way when we only have a few threads. Tough call...

How about
  4) Set an upper cap on the size of the raparm array

Readahead is only useful in moderation. You don't want to reach a
situation where the various threads' readahead activities start causing
thrashing...

Cheers
  Trond