Re: [PATCH 02/17] fs: icache lock s_inodes list

[Christoph Hellwig]

On Sun, Oct 17, 2010 at 04:09:11AM +1100, Nick Piggin wrote:
> If you want it to be scalable within a single sb, it needs to be
> per cpu. If it is per-cpu it does not need to be per-sb as well
> which just adds bloat.

Right now the patches split up the inode lock and do not add
per-cpu magic.  It's not any more work to move from per-sb lists
to per-cpu locking if we eventually do it than moving from global
to per-cpu.

I'm not entirely convinced moving s_inodes to a per-cpu list is a good
idea.  For now per-sb is just fine for disk filesystems as they have
much more fs-wide cachelines they touch for inode creatation/deletion
anyway, and for sockets/pipes a variant of your patch to not ever
add them to s_inodes sounds like the better approach.

If we eventually hit the limit for disk filesystems I have some better
ideas to solve this.  One is to abuse whatever data sturcture we use
for the inode hash also for iterating over all inodes - we only
iterate over them in very few places, and none of them is a fast path.

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