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Date: Tue, 24 Jan 2017 15:14:28 +0200
From: Konstantin Belousov <kostikbel@gmail.com>
To: Alexander Motin <mav@FreeBSD.org>
Cc: src-committers@freebsd.org, svn-src-all@freebsd.org,
 svn-src-head@freebsd.org
Subject: Re: svn commit: r312694 - in head: sys/cam/ctl usr.sbin/ctladm
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On Tue, Jan 24, 2017 at 12:13:41PM +0000, Alexander Motin wrote:
> Author: mav
> Date: Tue Jan 24 12:13:41 2017
> New Revision: 312694
> URL: https://svnweb.freebsd.org/changeset/base/312694
> 
> Log:
>   Make CTL ramdisk backend a real RAM disk.
>   
>   If "capacity" LU option is set, ramdisk backend now implements featured
>   thin provisioned disk, storing data in malloc(9) allocated memory blocks
>   of pblocksize bytes (default PAGE_SIZE or 4KB).  Additionally ~0.2% of LU
>   size is used for indirection tree (bigger pblocksize reduce the overhead).
>   Backend supports all unmap and anchor operations.  If configured capacity
>   is overflowed, proper error conditions are reported.
>   
>   If "capacity" LU option is not set, the backend operates mostly the same
>   as before without allocating real storage: writes go to nowhere, reads
>   return zeroes, reporting that all LBAs are unmapped.
>   
>   This backend is still mostly oriented on testing and benchmarking (it is
>   still a volatile RAM disk), but now it should allow to run real FS tests,
>   not only simple dumb dd.

This sounds too much like malloc-backed md(4).