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Date:	Thu, 7 Aug 2014 15:51:10 +0200
From:	Karel Zak <>
To:	Boaz Harrosh <>
Cc:	Ross Zwisler <>,
	Boaz Harrosh <>,
	Jens Axboe <>,
	Matthew Wilcox <>,
	linux-kernel <>,
	linux-fsdevel <>
Subject: Re: [PATCH 4/4] brd: Request from fdisk 4k alignment

On Thu, Aug 07, 2014 at 03:00:42PM +0200, Karel Zak wrote:
> On Thu, Aug 07, 2014 at 03:17:23PM +0300, Boaz Harrosh wrote:
> > > Is there an error case that this patch fixes?  I've had page alignment checks
> > > in my PRD direct_access code forever, and I don't know if they've ever
> > > tripped.  
> > > 
> > 
> > Yes! as I said above fix fdisk. You never tripped on it because partitions never
> > worked and you never tried them. With current code fdisk is very trigger happy
>  What do you mean with fdisk? which version?

Oh, I read all your email more carefully now, and if I good understand
the problem is what I/O limits the device provides to userspace rather
than with fdisk.

Anyway, I think you're right that alignment_offset is not the right
thing. It was introduced for backward compatibility with DOS-like
partitioning tools (~magical sector 63). I have doubts it's usable for
something else. For normal use-case should be enough to set proper
phy-sector size or min/optimal I/O limits (e.g. zram has all the
limits set to 4K(PAGE_SIZE)).

$ lsblk --topology /dev/zram0
zram0         0   4096   4096    4096    4096    0           128 128 0B


 Karel Zak  <>
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