Re: [rfc] lockless pagecache

[Nick Piggin <nickpiggin@yahoo.com.au>]

Hirokazu Takahashi wrote:
> Hi Nick,
> 

Hi,

> Your patches improve the performance if lots of processes are
> accessing the same file at the same time, right?
> 

Yes.

> If so, I think we can introduce multiple radix-trees instead,
> which enhance each inode to be able to have two or more radix-trees
> in it to avoid the race condition traversing the trees.
> Some decision mechanism is needed which radix-tree each page
> should be in, how many radix-tree should be prepared.
> 
> It seems to be simple and effective.
> 
> What do you think?
> 

Sure it is a possibility.

I don't think you could call it effective like a completely
lockless version is effective. You might take more locks during
gang lookups, you may have a lot of ugly and not-always-working
heuristics (hey, my app goes really fast if it spreads accesses
over a 1GB file, but falls on its face with a 10MB one). You
might get increased cache footprints for common operations.

I mainly did the patches for a bit of fun rather than to address
a particular problem with a real workload and as such I won't be
pushing to get them in the kernel for the time being.

-- 
SUSE Labs, Novell Inc.

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