BUG: REL 9.0 - MD malloc of custom sector size

[rank1seeker at gmail.com]

----- Original Message -----
From: RW <rwmaillists at googlemail.com>
To: freebsd-hackers at freebsd.org
Date: Sun, 18 Mar 2012 13:41:56 +0000
Subject: Re: BUG: REL 9.0 - MD malloc of custom sector size

> On Sun, 18 Mar 2012 14:01:39 +0100
> rank1seeker at gmail.com wrote:
> 
> > man mdconfig
> > ----
> > -S sectorsize to use for malloc backed device
> > ----
> > 
> > I want to create MD device, with sector size of 4 Kb.
> > 
> > It is CRITICAL to NOT append ANY suffixes, when specifing size, via
> > '-s' flag in order to use sectors, to set it's size. # mdconfig -a -t
> > malloc -S 4096 -s 32768
> > 
> > This should created dev of 128 Mb in size.
> > 32768 sectors * 4 Kb each = 131072 Kb = 128 Mb
> > Not! It created dev of 16 Mb in size, because sector size remained at
> > 512 bytes.
> 
> 
> From mdconfig 8
> 
> "Size is the number of 512 byte sectors unless ..."
> 
> Looks to me like it's doing what it said it would.
> 
> BTW are you sure you want to use  "-t malloc". This keeps the files
> (even the deleted ones) in memory unconditionally  while ordinary
> process memory is paged-out. 
> 

My MAIN reason to hassle with MD here, is to test a custom sector size.
This can be done with '-S' flag only, in order to set sectorsize of /dev/md*
But as it is malloc ONLY option/flag, I must combine it with '-t malloc'

Then I've defined it's size by amount of sectors and as I've redefined size of 1 sector, it simply isn't doing it's task.
Because it enforces hardcoded size of 512 bytes, so documentation should not misleadingly refer to sector in any way, but a hardcode value of 0.5 Kb, no matter of real/actual sector size is.



Domagoj Smolčić