Re: Lockless page cache test results

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

Andrew Morton wrote:

>>The top of the 4-client
>>vanilla run profile looks like this:
>>
>>samples  %        symbol name
>>65328    47.8972  find_get_page
>>
>>Basically the machine is fully pegged, about 7% idle time.
> 
> 
> Most of the time an acquisition of tree_lock is associated with a disk
> read, or a page-size memset, or a page-size memcpy.  And often an
> acquisition of tree_lock is associated with multiple pages, not just a
> single page.

Still, most of the times it is acquired would be once per page for
read, write, nopage.

For read and write, often it will be a full page memcpy but even such
a memcpy operation can quickly become insignificant compared to tl
contention.

Anyway, whatever. What needs to be demonstrated are real world
improvements at the end of the day.

> 
> So although the graph looks good, I wouldn't view this as a super-strong
> argument in favour of lockless pagecache.

No. Cool numbers though ;)

-- 
SUSE Labs, Novell Inc.

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