On Sun, May 7, 2017 at 9:20 AM, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > Hi Dan, > > 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. >> help >> Provide block layer support for the kernel. > > ... but it is not: now DAX is always enabled if you use block devices. > > $ bloat-o-meter vmlinux.nodax vmlinux.dax | head > add/remove: 59/0 grow/shrink: 10/1 up/down: 6048/-8 (6040) > function old new delta > dax_host_list - 4096 +4096 > alloc_dax - 306 +306 > dax_fs_init - 230 +230 > dax_get_by_host - 128 +128 > dax_sops - 100 +100 > dax_srcu - 90 +90 > dax_direct_access - 80 +80 > bdev_dax_pgoff - 80 +80 > > Does all block device access really needs DAX enabled? > > Furthermore: > > Maximum number of Device-DAX instances (NR_DEV_DAX) [32768] (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 > Location: > -> 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 alloc_chrdev_region().
