Re: Lockless page cache test results

[Nick Piggin]

Andrew Morton wrote:
> Jens Axboe <axboe@xxxxxxx> wrote:
>
> > Are there cases where the lockless page cache performs worse than the
> > current one?
>
>
> Yeah - when human beings try to understand and maintain it.

Have any tried yet? ;)

I won't deny it is complex (because I don't like when I make the
same point and people go on to take great trouble to convince me
how simple it is!).

But I hope it isn't _too_ bad. It is basically a dozen line
function at the core, and that gets used to implement
find_get_page, find_lock_page. Their semantics remain the same,
so that's where the line is drawn (plus minor things, like an
addition for reclaim's remove-from-pagecache protocol).

IMO the rcu radix tree is probably the most complex bit... but
that pales in comparison to things like our prio tree, or RCU
trie.

> The usual tradeoffs apply ;)

Definitely. It isn't fun if you just take the patch and merge it.

--
SUSE Labs, Novell Inc.
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