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

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Date:   Wed, 31 Aug 2016 15:36:07 -0600
From:   Ross Zwisler <ross.zwisler@...ux.intel.com>
To:     "Kani, Toshimitsu" <toshi.kani@....com>
Cc:     "ross.zwisler@...ux.intel.com" <ross.zwisler@...ux.intel.com>,
        "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 Wed, Aug 31, 2016 at 08:20:48PM +0000, Kani, Toshimitsu wrote:
> 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?

Yep, thanks for the report.