linux-ext4 - Re: [PATCH v2 0/9] re-enable DAX PMD support

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Date:   Wed, 31 Aug 2016 20:20:48 +0000
From:   "Kani, Toshimitsu" <toshi.kani@....com>
To:     "ross.zwisler@...ux.intel.com" <ross.zwisler@...ux.intel.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "adilger.kernel@...ger.ca" <adilger.kernel@...ger.ca>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mawilcox@...rosoft.com" <mawilcox@...rosoft.com>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "jack@...e.com" <jack@...e.com>, "tytso@....edu" <tytso@....edu>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
        "david@...morbit.com" <david@...morbit.com>
Subject: Re: [PATCH v2 0/9] re-enable DAX PMD support

On Tue, 2016-08-30 at 17:01 -0600, Ross Zwisler wrote:
> On Tue, Aug 23, 2016 at 04:04:10PM -0600, Ross Zwisler wrote:
> > 
> > DAX PMDs have been disabled since Jan Kara introduced DAX radix
> > tree based locking.  This series allows DAX PMDs to participate in
> > the DAX radix tree based locking scheme so that they can be re-
> > enabled.
> > 
> > Changes since v1:
> >  - PMD entry locking is now done based on the starting offset of
> > the PMD entry, rather than on the radix tree slot which was
> > unreliable. (Jan)
> >  - Fixed the one issue I could find with hole punch.  As far as I
> > can tell hole punch now works correctly for both PMD and PTE DAX
> > entries, 4k zero pages and huge zero pages.
> >  - Fixed the way that ext2 returns the size of holes in
> > ext2_get_block(). (Jan)
> >  - Made the 'wait_table' global variable static in respnse to a
> > sparse warning.
> >  - Fixed some more inconsitent usage between the names 'ret' and
> > 'entry' for radix tree entry variables.
> > 
> > Ross Zwisler (9):
> >   ext4: allow DAX writeback for hole punch
> >   ext2: tell DAX the size of allocation holes
> >   ext4: tell DAX the size of allocation holes
> >   dax: remove buffer_size_valid()
> >   dax: make 'wait_table' global variable static
> >   dax: consistent variable naming for DAX entries
> >   dax: coordinate locking for offsets in PMD range
> >   dax: re-enable DAX PMD support
> >   dax: remove "depends on BROKEN" from FS_DAX_PMD
> > 
> >  fs/Kconfig          |   1 -
> >  fs/dax.c            | 297 +++++++++++++++++++++++++++++-----------
> > ------------
> >  fs/ext2/inode.c     |   3 +
> >  fs/ext4/inode.c     |   7 +-
> >  include/linux/dax.h |  29 ++++-
> >  mm/filemap.c        |   6 +-
> >  6 files changed, 201 insertions(+), 142 deletions(-)
> > 
> > -- 
> > 2.9.0
> 
> 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?
Thanks,
-Toshi

[1] https://lkml.org/lkml/2016/8/29/560





View attachment "non-pmd.log" of type "text/x-log" (2306 bytes)

View attachment "pmd.log" of type "text/x-log" (2306 bytes)

View attachment "rc4.log" of type "text/x-log" (2338 bytes)