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Date:      Tue, 02 Sep 2014 12:23:56 -0500
From:      Alan Cox <alc@rice.edu>
To:        John Baldwin <jhb@freebsd.org>, Peter Wemm <peter@wemm.org>
Cc:        src-committers@freebsd.org, svn-src-all@freebsd.org, Dmitry Morozovsky <marck@rinet.ru>, "Matthew D. Fuller" <fullermd@over-yonder.net>, svn-src-head@freebsd.org, Steven Hartland <smh@freebsd.org>
Subject:   Re: svn commit: r270759 - in head/sys: cddl/compat/opensolaris/kern cddl/compat/opensolaris/sys cddl/contrib/opensolaris/uts/common/fs/zfs vm
Message-ID:  <5405FD2C.8000901@rice.edu>
In-Reply-To: <201409021201.15967.jhb@freebsd.org>
References:  <201408281950.s7SJo90I047213@svn.freebsd.org> <E0F163ECBF5E407F99AFDB18FAB05C58@multiplay.co.uk> <39211177.i8nn9sHiCx@overcee.wemm.org> <201409021201.15967.jhb@freebsd.org>

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On 09/02/2014 11:01, John Baldwin wrote:
> On Saturday, August 30, 2014 1:37:43 pm Peter Wemm wrote:
>> On Saturday 30 August 2014 02:03:42 Steven Hartland wrote:
>> I'm very disappointed in the attention to detail and errors in the commit.  
>> I'm almost at the point where I want to ask for the whole thing to be backed 
>> out.
> I would not be too supportive of that.  This PR has been open for a long, long 
> time with many users using patches from it in production loads that were 
> greatly improved by the changes and clamoring on the lists multiple times to 
> get someone to look at it.  avg@ contributed quite a bit of time to diagnose 
> this with Karl early on, but other developers aside from Steven did not.  It 
> also was not hard to explain to Karl the meaning of 'cache + free' in the bug 
> follow-ups itself (though I believe avg@ had tried this before and it didn't 
> sink in that time for some reason).
>
> I know Steven has since committed a fix, but if there are still concerns, I 
> think it would be best to not just revert this entirely but to spend some time  
> fixing the remaining issues.  Clearly this issue affects a lot of users and 
> the earlier fixes to pagedaemon were not sufficient to fix their issues alone.
>

The patch actually makes two completely orthogonal changes at once, and
one of those changes has no connection to the page daemon.  I suspect
that is why some people have said that their issues were not addressed
by the page daemon fix.

Prior to this patch, we were limiting the ARC size to 3/4 the kmem
map/arena/object size on all architectures, including 64-bit,
uma_small_alloc-enabled architectures where such a limit makes no
sense.  Consequently, some people were complaining, "Why is 1/4 of my
memory going unused?"





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