linux-kernel - Re: [PATCH v2 1/6] dax: Add block size note to documentation

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Message-ID: <5598EE47.1030204@gmail.com>
Date:	Sun, 05 Jul 2015 11:43:51 +0300
From:	Boaz Harrosh <openosd@...il.com>
To:	Christoph Hellwig <hch@...radead.org>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>
CC:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Matthew Wilcox <willy@...ux.intel.com>
Subject: Re: [PATCH v2 1/6] dax: Add block size note to documentation

On 07/04/2015 08:03 AM, Christoph Hellwig wrote:
> On Fri, Jul 03, 2015 at 10:40:38AM -0400, Matthew Wilcox wrote:
>> From: Matthew Wilcox <willy@...ux.intel.com>
>>
>> For block devices which are small enough, mkfs will default to creating
>> a filesystem with block sizes smaller than page size.
> 
> This seems like an odd note.  At least for XFS and btrfs filesystem size
> don't change block sizes.  ff this is an extN oddity you're probably
> better off documenting it there.
> 

Is why I added to brd:
	/* This is so fdisk will align partitions on 4k, because of
	 * direct_access API needing 4k alignment, returning a PFN
	 * (This is only a problem on very small devices <= 4M,
	 *  otherwise fdisk will align on 1M. Regardless this call
	 *  is harmless)
	 */
	blk_queue_physical_block_size(brd->brd_queue, PAGE_SIZE);

Perhaps add the same to pmem, and/or perhaps make mkfs.extX
also inspect this and not create blocks smaller then physical_block_size?

Thanks
Boaz

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