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Date:      Sun, 23 Aug 2020 15:16:14 -0400
From:      Mark Johnston <markj@freebsd.org>
To:        Ian Lepore <ian@freebsd.org>
Cc:        guyvert@secmail.pro, freebsd-hackers@freebsd.org
Subject:   Re: Running BSD from RAM memory using zroot
Message-ID:  <20200823191614.GD1954@raichu>
In-Reply-To: <6e395923c808ccc34f5f88efffd7853baef1d3ec.camel@freebsd.org>
References:  <6a7da06949dbd8f1c38d5faa22f3f28b.squirrel@giyzk7o6dcunb2ry.onion> <6e395923c808ccc34f5f88efffd7853baef1d3ec.camel@freebsd.org>

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On Sun, Aug 23, 2020 at 12:26:07PM -0600, Ian Lepore wrote:
> Note that deleting md0 will not necessarily
> make the memory it was using available for further use.  The memory
> will be in the form of a preloaded module, and it's not clear to me
> that it can be unloaded (but I'm also not sure that it can't be).

On i386 and amd64 preloaded memory can be freed, see
kmem_bootstrap_free().  On other platforms it is leaked.  It is not too
hard to fix for a given platform, the pmap needs to ensure that pages
containing preloaded data and the page table pages mapping preloaded
data are initialized properly.  See r336505 for an example.



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