Re: BLOCK selects DAX (was: Re: dax: introduce dax_direct_access())
From: Geert Uytterhoeven
Date: Sun May 07 2017 - 17:52:08 EST
On Sun, May 7, 2017 at 8:26 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> On Sun, May 7, 2017 at 9:20 AM, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
>> On Sat, May 6, 2017 at 4:21 AM, Linux Kernel Mailing List
>> <linux-kernel@xxxxxxxxxxxxxxx> wrote:
>>> Web: https://git.kernel.org/torvalds/c/b0686260fecaa924d8eff2ace94bee70506bc308
>>> Commit: b0686260fecaa924d8eff2ace94bee70506bc308
>>> Parent: d8f07aee3f2fd959878bf614d4e984900018eb9e
>>> Refname: refs/heads/master
>>> Author: Dan Williams <dan.j.williams@xxxxxxxxx>
>>> AuthorDate: Thu Jan 26 20:37:35 2017 -0800
>>> Committer: Dan Williams <dan.j.williams@xxxxxxxxx>
>>> CommitDate: Thu Apr 20 11:57:52 2017 -0700
>>> dax: introduce dax_direct_access()
>>> Replace bdev_direct_access() with dax_direct_access() that uses
>>> dax_device and dax_operations instead of a block_device and
>>> block_device_operations for dax. Once all consumers of the old api have
>>> been converted bdev_direct_access() will be deleted.
>>> Given that block device partitioning decisions can cause dax page
>>> alignment constraints to be violated this also introduces the
>>> bdev_dax_pgoff() helper. It handles calculating a logical pgoff relative
>>> to the dax_device and also checks for page alignment.
>>> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
>> This looks like a fairly innocent change...
>>> block/Kconfig | 1 +
>>> drivers/dax/super.c | 39 +++++++++++++++++++++++++++++++++++++++
>>> fs/block_dev.c | 14 ++++++++++++++
>>> include/linux/blkdev.h | 1 +
>>> include/linux/dax.h | 2 ++
>>> 5 files changed, 57 insertions(+)
>>> diff --git a/block/Kconfig b/block/Kconfig
>>> index e9f780f815f5..93da7fc3f254 100644
>>> --- a/block/Kconfig
>>> +++ b/block/Kconfig
>>> @@ -6,6 +6,7 @@ menuconfig BLOCK
>>> default y
>>> select SBITMAP
>>> select SRCU
>>> + select DAX
> Whoops, yes, that should be "select DAX if FS_DAX". We don't need the
> DAX core if we're never going to mount a DAX capable filesystem.
>> Maximum number of Device-DAX instances (NR_DEV_DAX)  (NEW) ?
>> There is no help available for this option.
>> Symbol: NR_DEV_DAX [=32768]
>> Type : integer
>> Range : [256 2147483647]
>> Prompt: Maximum number of Device-DAX instances
>> -> Device Drivers
>> -> DAX: direct access to differentiated memory (DAX [=y])
>> Defined at drivers/dax/Kconfig:31
>> Depends on: DAX [=y]
>> What should I answer here?
>> "256" already sounds like a large number to me, "32768" sounds huge, and
>> "2147483647" sounds insane? But perhaps this doesn't really mean what I
>> would expect...
>> Can you please add some help for this option?
> Will do. The number gets passed directly to the @count parameter of
BTW, I saw that. But it still didn't give me a clue about a useful value.
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds