Re: Lockless page cache test results

[Nick Piggin]

Nick Piggin wrote:
> Jens Axboe wrote:
>
> > Things look pretty bad for the lockless kernel though, Nick any idea
> > what is going on there? The splice change is pretty simple, see the top
> > three patches here:
>
>
> Could just be the use of spin lock instead of read lock.
>
> I don't think it would be hard to convert find_get_pages_contig
> to be lockless.
>
> Patched vanilla numbers look nicer, but I'm curious as to why
> __do_page_cache was so bad before, if the file was in cache.
> Presumably it should not more than double tree_lock acquisition...
> it isn't getting called multiple times for each page, is it?

Hmm, what's more, find_get_pages_contig shouldn't result in any
fewer tree_lock acquires than the open coded thing there now
(for the densely populated pagecache case).

--
SUSE Labs, Novell Inc.
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