On Mon, Jul 19, 2021 at 12:34:53PM +0200, Christoph Hellwig wrote:
> Hi all,
>
> this series replies the existing callback-based iomap_apply to an iter based
> model. The prime aim here is to simply the DAX reflink support, which
> requires iterating through two inodes, something that is rather painful
> with the apply model. It also helps to kill an indirect call per segment
> as-is. Compared to the earlier patchset from Matthew Wilcox that this
> series is based upon it does not eliminate all indirect calls, but as the
> upside it does not change the file systems at all (except for the btrfs
> and gfs2 hooks which have slight prototype changes).
FWIW patches 9-20 look ok to me, modulo the discussion I started in
patch 8 about defining a distinct type for iomap byte lengths instead of
the combination of int/ssize_t/u64 that we use now.
> This passes basic testing on XFS for block based file systems. The DAX
> changes are entirely untested as I haven't managed to get pmem work in
> recent qemu.
This gets increasingly difficult as time goes by.
Right now I have the following bits of libvirt xml in the vm
definitions:
<maxMemory slots='32' unit='KiB'>1073741824</maxMemory>
<devices>
<memory model='nvdimm' access='shared'>
<source>
<path>/run/g.mem</path>
</source>
<target>
<size unit='KiB'>10487808</size>
<node>0</node>
</target>
<address type='dimm' slot='0'/>
</memory>
</devices>
Which seems to translate to:
-machine pc-q35-4.2,accel=kvm,usb=off,vmport=off,dump-guest-core=off,nvdimm=on
-object memory-backend-file,id=memnvdimm0,prealloc=no,mem-path=/run/g.mem,share=yes,size=10739515392,align=128M
-device nvdimm,memdev=memnvdimm0,id=nvdimm0,slot=0,label-size=2M
Evidently something was added to the pmem code(?) that makes it fussy if
the memory region doesn't align to a 128M boundary or the label isn't
big enough for ... whatever gets written into them.
The file /run/g.mem is intended to provide 10GB of pmem to the VM, with
an additional 2M allocated for the label.
--D
> Diffstat:
> b/fs/btrfs/inode.c | 5
> b/fs/buffer.c | 4
> b/fs/dax.c | 578 ++++++++++++++++++++++-------------------------
> b/fs/gfs2/bmap.c | 5
> b/fs/internal.h | 4
> b/fs/iomap/Makefile | 2
> b/fs/iomap/buffered-io.c | 344 +++++++++++++--------------
> b/fs/iomap/direct-io.c | 162 ++++++-------
> b/fs/iomap/fiemap.c | 101 +++-----
> b/fs/iomap/iter.c | 74 ++++++
> b/fs/iomap/seek.c | 88 +++----
> b/fs/iomap/swapfile.c | 38 +--
> b/fs/iomap/trace.h | 35 +-
> b/include/linux/iomap.h | 73 ++++-
> fs/iomap/apply.c | 99 --------
> 15 files changed, 777 insertions(+), 835 deletions(-)
