linux-kernel - Re: [PATCH v4 6/6] block: Update blkdev_dax

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Date:	Wed, 11 May 2016 17:26:46 +0200
From:	Jan Kara <jack@...e.cz>
To:	Toshi Kani <toshi.kani@....com>
Cc:	Jan Kara <jack@...e.cz>, dan.j.williams@...el.com,
	david@...morbit.com, viro@...iv.linux.org.uk, axboe@...com,
	hch@...radead.org, boaz@...xistor.com, tytso@....edu,
	adilger.kernel@...ger.ca, ross.zwisler@...ux.intel.com,
	micah.parrish@....com, linux-nvdimm@...ts.01.org,
	linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 6/6] block: Update blkdev_dax_capable() for consistency

On Wed 11-05-16 08:25:10, Toshi Kani wrote:
> On Wed, 2016-05-11 at 10:05 +0200, Jan Kara wrote:
> > On Tue 10-05-16 10:23:57, Toshi Kani wrote:
> > > 
> > > blkdev_dax_capable() is similar to bdev_dax_supported(), but needs
> > > to remain as a separate interface for checking dax capability of
> > > a raw block device.
> > > 
> > > Rename and relocate blkdev_dax_capable() to keep them maintained
> > > consistently, and call bdev_direct_access() for the dax capability
> > > check.
> > ...
> > > 
> > > +bool bdev_dax_capable(struct block_device *bdev)
> > > +{
> > > +	struct gendisk *disk = bdev->bd_disk;
> > > +	struct blk_dax_ctl dax = {
> > > +		.size = PAGE_SIZE,
> > > +	};
> > > +
> > > +	if (!IS_ENABLED(CONFIG_FS_DAX))
> > > +		return false;
> >
> > Frankly, I prefer the #ifdef CONFIG_FS_DAX and just compile the code out
> > when DAX is not enabled (like it was with blkdev_dax_capable()). That way
> > we don't grow the kernel for people who don't care about DAX.
> 
> When CONFIG_FS_DAX is not set, the rest of the code is optimized out.  So,
> I think the code size is the same.
> 
> (gdb) disas bdev_dax_capable
> Dump of assembler code for function bdev_dax_capable:
>    0xffffffff81260d20 <+0>:     callq  0xffffffff81813c30 <__fentry__>
>    0xffffffff81260d25 <+5>:     push   %rbp
>    0xffffffff81260d26 <+6>:     xor    %eax,%eax
>    0xffffffff81260d28 <+8>:     mov    %rsp,%rbp
>    0xffffffff81260d2b <+11>:    pop    %rbp
>    0xffffffff81260d2c <+12>:    retq   
> End of assembler dump.

Ah, good. So feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR