Change uma_mtx to rwlock

[Steven Hartland]

Out of interest does that include ZFS and its UMA zones, as we're currently
investigating issues around this.

    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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