On Sat, Feb 23, 2019 at 10:11:36AM +1100, Dave Chinner wrote:
> On Fri, Feb 22, 2019 at 10:20:08AM -0800, Darrick J. Wong wrote:
> > Hi all!
> >
> > Uh, we have an internal customer <cough> who's been trying out MAP_SYNC
> > on pmem, and they've observed that one has to do a fair amount of
> > legwork (in the form of mkfs.xfs parameters) to get the kernel to set up
> > 2M PMD mappings. They (of course) want to mmap hundreds of GB of pmem,
> > so the PMD mappings are much more efficient.
> >
> > I started poking around w.r.t. what mkfs.xfs was doing and realized that
> > if the fsdax pmem device advertised iomin/ioopt of 2MB, then mkfs will
> > set up all the parameters automatically. Below is my ham-handed attempt
> > to teach the kernel to do this.
>
> What's the before and after mkfs output?
>
> (need to see the context that this "fixes" before I comment)
Here's what we do today assuming no options and 800GB pmem devices:
# blockdev --getiomin --getioopt /dev/pmem0 /dev/pmem1
4096
0
4096
0
# mkfs.xfs -N /dev/pmem0 -r rtdev=/dev/pmem1
meta-data=/dev/pmem0 isize=512 agcount=4, agsize=52428800 blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=1, sparse=1, rmapbt=0
= reflink=0
data = bsize=4096 blocks=209715200, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0, ftype=1
log =internal log bsize=4096 blocks=102400, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =/dev/pmem1 extsz=4096 blocks=209715200, rtextents=209715200
And here's what we do to get 2M aligned mappings:
# mkfs.xfs -N /dev/pmem0 -r rtdev=/dev/pmem1,extsize=2m -d su=2m,sw=1
meta-data=/dev/pmem0 isize=512 agcount=32, agsize=6553600 blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=1, sparse=1, rmapbt=0
= reflink=0
data = bsize=4096 blocks=209715200, imaxpct=25
= sunit=512 swidth=512 blks
naming =version 2 bsize=4096 ascii-ci=0, ftype=1
log =internal log bsize=4096 blocks=102400, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =/dev/pmem1 extsz=2097152 blocks=209715200, rtextents=409600
With this patch, things change as such:
# blockdev --getiomin --getioopt /dev/pmem0 /dev/pmem1
2097152
2097152
2097152
2097152
# mkfs.xfs -N /dev/pmem0 -r rtdev=/dev/pmem1
meta-data=/dev/pmem0 isize=512 agcount=32, agsize=6553600 blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=1, sparse=1, rmapbt=0
= reflink=0
data = bsize=4096 blocks=209715200, imaxpct=25
= sunit=512 swidth=512 blks
naming =version 2 bsize=4096 ascii-ci=0, ftype=1
log =internal log bsize=4096 blocks=102400, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =/dev/pmem1 extsz=2097152 blocks=209715200, rtextents=409600
I think the only change is the agcount, which for 2M mappings probably
isn't a huge deal. It's obviously a bigger deal for 1G pages, assuming
we decide that's even advisable.
--D
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@xxxxxxxxxxxxx
