Hello,
I noticed that DAX 2MB mmap no longer works on XFS. I used the
following steps on a 4.15-rc7 kernel. Am I missing something, or is
there a problem in XFS?
# mkfs.xfs -f -d su=2m,sw=1 /dev/pmem0
# mount -o dax /dev/pmem0 /mnt/pmem0
# xfs_io -c "extsize 2m" /mnt/pmem0
fio with libpmem engine (which uses mmap) is slow since it gets
serialized by 4KB page faults.
# numactl --cpunodebind=0 --membind=0 fio --filename=/mnt/pmem0/testfile
--rw=read --ioengine=libpmem --iodepth=1 --numjobs=16 --runtime=60 --
group_reporting --name=perf_test --thread=1 --size=6g --bs=128k --
direct=1
:
Run status group 0 (all jobs):
READ: bw=4357MiB/s (4569MB/s), 4357MiB/s-4357MiB/s (4569MB/s-
4569MB/s), io=96.0GiB (103GB), run=22560-22560msec
Resulted file blocks in "testfile" are not aligned by 2MB.
# filefrag -v /mnt/pmem0/testfile
Filesystem type is: 58465342
File size of testfile is 6442450944 (1572864 blocks of 4096 bytes)
ext: logical_offset: physical_offset: length: expected:
flags:
0: 0.. 261111: 520.. 261631: 261112:
1: 261112.. 261348: 12.. 248: 237: 261632:
2: 261349.. 522705: 261644.. 523000: 261357: 249:
3: 522706.. 784062: 523276.. 784632: 261357: 523001:
4: 784063.. 1045419: 784908.. 1046264: 261357: 784633:
5: 1045420.. 1304216: 1049100.. 1307896: 258797: 1046265:
6: 1304217.. 1565573: 1308172.. 1569528: 261357: 1307897:
7: 1565574.. 1572863: 1570304.. 1577593: 7290: 1569529:
last,eof
testfile: 8 extents found
A file created by fallocate also shows that physical offset starts from
520, which is not aligned by 2MB.
# fallocate --length 1G /mnt/pmem0/data
# filefrag -v /mnt/pmem0/data
Filesystem type is: 58465342
File size of /mnt/pmem0/data is 1073741824 (262144 blocks of 4096 bytes)
ext: logical_offset: physical_offset: length: expected:
flags:
0: 0.. 260607: 520.. 261127:
260608: unwritten
1: 260608.. 262143: 262144.. 263679: 1536: 261128:
last,unwritten,eof
/mnt/pmem0/data: 2 extents found
ext4 does not have the issue in the same steps.
# mkfs.ext4 -b 4096 -E stride=512 -F /dev/pmem1
# mount -o dax /dev/pmem1 /mnt/pmem1
# numactl --cpunodebind=0 --membind=0 fio --filename=/mnt/pmem1/testfile
--rw=read --ioengine=libpmem --iodepth=1 --numjobs=16 --runtime=60 --
group_reporting --name=perf_test --thread=1 --size=6g --bs=128k --
direct=1
:
Run status group 0 (all jobs):
READ: bw=44.4GiB/s (47.7GB/s), 44.4GiB/s-44.4GiB/s (47.7GB/s-
47.7GB/s), io=96.0GiB (103GB), run=2160-2160msec
All blocks are aligned by 2MB.
# filefrag -v /ment/pmem1/testfile
Filesystem type is: ef53
File size of testfile is 6442450944 (1572864 blocks of 4096 bytes)
ext: logical_offset: physical_offset: length: expected:
flags:
0: 0.. 32767: 34816.. 67583: 32768:
1: 32768.. 63487: 67584.. 98303: 30720:
2: 63488.. 96255: 100352.. 133119: 32768: 98304:
3: 96256.. 126975: 133120.. 163839: 30720:
:
# fallocate --length 1G /mnt/pmem1/data
# filefrag -v /mnt/pmem1/data
Filesystem type is: ef53
File size of /mnt/pmem1/data is 1073741824 (262144 blocks of 4096 bytes)
ext: logical_offset: physical_offset: length: expected:
flags:
0: 0.. 30719: 34816.. 65535: 30720: unwritten
1: 30720.. 61439: 65536.. 96255: 30720: unwritten
2: 61440.. 63487: 96256.. 98303: 2048: unwritten
:
Thanks,
-Toshi
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