Change uma_mtx to rwlock

[Bryan Venteicher]

On Sat, Sep 27, 2014 at 8:42 PM, Steven Hartland <killing at multiplay.co.uk>
wrote:

> Out of interest does that include ZFS and its UMA zones, as we're currently
> investigating issues around this.
>
>
​Yes, I believe this would include ZFS's zones too.​



>    Regards
>    Steve
>
> ----- Original Message ----- From: "Bryan Venteicher" <
> bryanv at daemoninthecloset.org>
> To: <freebsd-hackers at freebsd.org>
> Sent: Sunday, September 28, 2014 1:59 AM
> Subject: Change uma_mtx to rwlock
>
>
>
>  Hi,
>>
>> I'd appreciate some comments attached patch that changes the uma_mtx to a
>> rwlock.
>>
>> At $JOB, we have machines with ~400GB RAM, with much of that being
>> allocated through UMA zones. We've observed that timeouts were sometimes
>> unexpectedly delayed by a half second or more. We tracked one of the
>> reasons for this down to when the page daemon was running, calling
>> uma_reclaim() -> zone_foreach(). zone_foreach() holds the uma_mtx while
>> zone_drain()'ing each zone. If uma_timeout() fires, it will block on the
>> uma_mtx when it tries to zone_timeout() each zone.
>>
>>
>
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>