linux-ext4 - [PATCH v2 0/3] 1G transparent hugepage support for device dax

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Date:   Thu, 26 Jan 2017 10:09:41 -0700
From:   Dave Jiang <dave.jiang@...el.com>
To:     akpm@...ux-foundation.org
Cc:     dave.hansen@...ux.intel.com, mawilcox@...rosoft.com,
        linux-nvdimm@...ts.01.org, linux-xfs@...r.kernel.org,
        linux-mm@...ck.org, vbabka@...e.cz, jack@...e.com,
        dan.j.williams@...el.com, linux-ext4@...r.kernel.org,
        ross.zwisler@...ux.intel.com, kirill.shutemov@...ux.intel.com
Subject: [PATCH v2 0/3] 1G transparent hugepage support for device dax

The following series implements support for 1G trasparent hugepage on
x86 for device dax. The bulk of the code was written by Mathew Wilcox
a while back supporting transparent 1G hugepage for fs DAX. I have
forward ported the relevant bits to 4.10-rc. The current submission has
only the necessary code to support device DAX.

Comments from Dan Williams:
So the motivation and intended user of this functionality mirrors the
motivation and users of 1GB page support in hugetlbfs. Given expected
capacities of persistent memory devices an in-memory database may want
to reduce tlb pressure beyond what they can already achieve with 2MB
mappings of a device-dax file. We have customer feedback to that
effect as Willy mentioned in his previous version of these patches
[1].

[1]: https://lkml.org/lkml/2016/1/31/52

Comments from Nilesh @ Oracle:

There are applications which have a process model; and if you assume 10,000
processes attempting to mmap all the 6TB memory available on a server;
we are looking at the following:

processes         : 10,000
memory            :    6TB
pte @ 4k page size: 8 bytes / 4K of memory * #processes = 6TB / 4k * 8 * 10000 = 1.5GB * 80000 = 120,000GB
pmd @ 2M page size: 120,000 / 512 = ~240GB
pud @ 1G page size: 240GB / 512 = ~480MB

As you can see with 2M pages, this system will use up an
exorbitant amount of DRAM to hold the page tables; but the 1G
pages finally brings it down to a reasonable level.
Memory sizes will keep increasing; so this number will keep
increasing.

An argument can be made to convert the applications from process
model to thread model, but in the real world that may not be
always practical.
Hopefully this helps explain the use case where this is valuable.

v2: Fixup build issues from 0-day build.

---

Dave Jiang (1):
      dax: Support for transparent PUD pages for device DAX

Matthew Wilcox (2):
      mm,fs,dax: Change ->pmd_fault to ->huge_fault
      mm,x86: Add support for PUD-sized transparent hugepages

 arch/Kconfig                          |    3 
 arch/x86/Kconfig                      |    1 
 arch/x86/include/asm/paravirt.h       |   11 +
 arch/x86/include/asm/paravirt_types.h |    2 
 arch/x86/include/asm/pgtable-2level.h |   17 ++
 arch/x86/include/asm/pgtable-3level.h |   24 +++
 arch/x86/include/asm/pgtable.h        |  140 +++++++++++++++++++
 arch/x86/include/asm/pgtable_64.h     |   15 ++
 arch/x86/kernel/paravirt.c            |    1 
 arch/x86/mm/pgtable.c                 |   31 ++++
 drivers/dax/dax.c                     |   82 ++++++++---
 fs/dax.c                              |   43 ++++--
 fs/ext2/file.c                        |    2 
 fs/ext4/file.c                        |    6 -
 fs/xfs/xfs_file.c                     |   10 +
 fs/xfs/xfs_trace.h                    |    2 
 include/asm-generic/pgtable.h         |   80 ++++++++++-
 include/asm-generic/tlb.h             |   14 ++
 include/linux/dax.h                   |    6 -
 include/linux/huge_mm.h               |   83 ++++++++++-
 include/linux/mm.h                    |   40 +++++
 include/linux/mmu_notifier.h          |   14 ++
 include/linux/pfn_t.h                 |   12 ++
 mm/gup.c                              |    7 +
 mm/huge_memory.c                      |  249 +++++++++++++++++++++++++++++++++
 mm/memory.c                           |  102 ++++++++++++--
 mm/pagewalk.c                         |   20 +++
 mm/pgtable-generic.c                  |   14 ++
 28 files changed, 956 insertions(+), 75 deletions(-)