Re: [PATCH v3 0/8] Support for transparent PUD pages for DAX files

[mingming cao]

On 01/08/2016 11:49 AM, Matthew Wilcox wrote:
> From: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
> 
> Andrew, I think this is ready for a spin in -mm.
> 
> v3: Rebased against current mmtom
> v2: Reduced churn in filesystems by switching to ->huge_fault interface
>     Addressed concerns from Kirill
> 
> We have customer demand to use 1GB pages to map DAX files.  Unlike the 2MB
> page support, the Linux MM does not currently support PUD pages, so I have
> attempted to add support for the necessary pieces for DAX huge PUD pages.
> 
> Filesystems still need work to allocate 1GB pages.  With ext4, I can
> only get 16MB of contiguous space, although it is aligned.  With XFS,
> I can get 80MB less than 1GB, and it's not aligned.  The XFS problem
> may be due to the small amount of RAM in my test machine.
> 
I dont think ext4 can do 1G at this time due to extent length bits (15 for unwritten) and block group size bundary (well, with flex bg we may able to relax this ). I have seen about 125M of contiguous space allocated on my fresh new ext4 filesystem. I do remember mballoc in ext4 used to normalize the allocation request up to 8 or 16M, but it appears not that small any more.

Thanks,
Mingming

> This patch set is against something approximately current -mm.  I'd like
> to thank Dave Chinner & Kirill Shutemov for their reviews of v1.
> The conversion of pmd_fault & pud_fault to huge_fault is thanks to
> Dave's poking, and Kirill spotted a couple of problems in the MM code.
> Version 2 of the patch set is about 200 lines smaller (1016 insertions,
> 23 deletions in v1).
> 
> I've done some light testing using a program to mmap a block device
> with DAX enabled, calling mincore() and examining /proc/smaps and
> /proc/pagemap.
> 
> Matthew Wilcox (8):
>   mm: Convert an open-coded VM_BUG_ON_VMA
>   mm,fs,dax: Change ->pmd_fault to ->huge_fault
>   mm: Add support for PUD-sized transparent hugepages
>   mincore: Add support for PUDs
>   procfs: Add support for PUDs to smaps, clear_refs and pagemap
>   x86: Add support for PUD-sized transparent hugepages
>   dax: Support for transparent PUD pages
>   ext4: Support for PUD-sized transparent huge pages
> 
>  Documentation/filesystems/dax.txt     |  12 +-
>  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.h        |  94 ++++++++++++
>  arch/x86/include/asm/pgtable_64.h     |  13 ++
>  arch/x86/kernel/paravirt.c            |   1 +
>  arch/x86/mm/pgtable.c                 |  31 ++++
>  fs/block_dev.c                        |  10 +-
>  fs/dax.c                              | 272 +++++++++++++++++++++++++---------
>  fs/ext2/file.c                        |  27 +---
>  fs/ext4/file.c                        |  60 +++-----
>  fs/proc/task_mmu.c                    | 109 ++++++++++++++
>  fs/xfs/xfs_file.c                     |  25 ++--
>  fs/xfs/xfs_trace.h                    |   2 +-
>  include/asm-generic/pgtable.h         |  62 +++++++-
>  include/asm-generic/tlb.h             |  14 ++
>  include/linux/dax.h                   |  17 ---
>  include/linux/huge_mm.h               |  50 +++++++
>  include/linux/mm.h                    |  43 +++++-
>  include/linux/mmu_notifier.h          |  13 ++
>  include/linux/pfn_t.h                 |   8 +
>  mm/huge_memory.c                      | 151 +++++++++++++++++++
>  mm/memory.c                           | 101 +++++++++++--
>  mm/mincore.c                          |  13 ++
>  mm/pagewalk.c                         |  19 ++-
>  mm/pgtable-generic.c                  |  14 ++
>  28 files changed, 980 insertions(+), 198 deletions(-)
>