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Date:      Fri, 21 Nov 2014 12:25:39 -0800
From:      Xin Li <delphij@delphij.net>
To:        Andriy Gapon <avg@FreeBSD.org>, Xin LI <delphij@FreeBSD.org>,  src-committers@FreeBSD.org, svn-src-all@FreeBSD.org,  svn-src-head@FreeBSD.org
Subject:   Re: svn commit: r273060 - head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs
Message-ID:  <546F9FC3.10402@delphij.net>
In-Reply-To: <546F57B1.2020602@FreeBSD.org>
References:  <201410132039.s9DKdpmh055573@svn.freebsd.org> <546F57B1.2020602@FreeBSD.org>

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On 11/21/14 07:18, Andriy Gapon wrote:
> On 13/10/2014 23:39, Xin LI wrote:
>> Author: delphij Date: Mon Oct 13 20:39:51 2014 New Revision:
>> 273060 URL: https://svnweb.freebsd.org/changeset/base/273060
>> 
>> Log: Use write_psize instead of write_asize when doing
>> vdev_space_update. Without this change the accounting of L2ARC
>> usage would be wrong and give 16EB free space because the number
>> became negative and overflows.
>> 
>> Obtained from:	FreeNAS (issue #6239)
> 
> First, a link to the issue would be more convenient for reviewers.
> Here it is https://bugs.freenas.org/issues/6239
> 
> Then, I would like to see a technical explanation for this change. 
> I could not find any explanation here or in the FreeNAS issue or in
> the FreeNAS commit.
> 
> As far as I can see, all calls to vdev_space_update() in the ARC
> code are passed l2hdr->b_asize or a sum of b_asize fields of
> multiple buffers. Thus, I am really surprised with this change and
> would like to see reasoning behind it.

Hmm I think you are right that my change doesn't make sense but I
can't remember the details either and suggests there is some other
issues that was covered up by this.

It looks like that I was confused because the L2ARC clock hand
advances by buf_p_sz (unrelated but it should really be called
buf_a_size) and the way we calculate allocated L2ARC free.

Cheers,
- -- 
Xin LI <delphij@delphij.net>    https://www.delphij.net/
FreeBSD - The Power to Serve!           Live free or die
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