On Wed, 2016-08-31 at 15:36 -0600, Ross Zwisler wrote:

On Wed, Aug 31, 2016 at 08:20:48PM +0000, Kani, Toshimitsu wrote:

quoted

On Tue, 2016-08-30 at 17:01 -0600, Ross Zwisler wrote:

quoted

On Tue, Aug 23, 2016 at 04:04:10PM -0600, Ross Zwisler wrote:

 :

quoted

quoted

Ping on this series?  Any objections or comments?

Hi Ross,

I am seeing a major performance loss in fio mmap test with this
patch-set applied.  This happens with or without my patches [1]
applied on top of yours.  Without my patches, dax_pmd_fault() falls
back to the pte handler since an mmap'ed address is not 2MB-
aligned.

I have attached three test results.
 o rc4.log - 4.8.0-rc4 (base)
 o non-pmd.log - 4.8.0-rc4 + your patchset (fall back to pte)
 o pmd.log - 4.8.0-rc4 + your patchset + my patchset (use pmd maps)

My test steps are as follows.

mkfs.ext4 -O bigalloc -C 2M /dev/pmem0
mount -o dax /dev/pmem0 /mnt/pmem0
numactl --preferred block:pmem0 --cpunodebind block:pmem0 fio
test.fio

"test.fio"
---
[global]
bs=4k
size=2G
directory=/mnt/pmem0
ioengine=mmap
[randrw]
rw=randrw
---

Can you please take a look?

Yep, thanks for the report.

I have some more observations.  It seems this issue is related with pmd
mappings after all.  fio creates "randrw.0.0" file.  In my setup, an
initial test run creates pmd mappings and hits this issue.  Subsequent
test runs (i.e. randrw.0.0 exists), without my patches, fall back to
pte mappings and do not hit this issue.  With my patches applied,
subsequent runs still create pmd mappings and hit this issue.

Thanks,
-Toshi  






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