• Dave Jiang's avatar
    mm,fs,dax: change ->pmd_fault to ->huge_fault · a2d58167
    Dave Jiang authored
    Patch series "1G transparent hugepage support for device dax", v2.
    
    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.
    
    This patch (of 3):
    
    In preparation for adding the ability to handle PUD pages, convert
    vm_operations_struct.pmd_fault to vm_operations_struct.huge_fault.  The
    vm_fault structure is extended to include a union of the different page
    table pointers that may be needed, and three flag bits are reserved to
    indicate which type of pointer is in the union.
    
    [ross.zwisler@linux.intel.com: remove unused function ext4_dax_huge_fault()]
      Link: http://lkml.kernel.org/r/1485813172-7284-1-git-send-email-ross.zwisler@linux.intel.com
    [dave.jiang@intel.com: clear PMD or PUD size flags when in fall through path]
      Link: http://lkml.kernel.org/r/148589842696.5820.16078080610311444794.stgit@djiang5-desk3.ch.intel.com
    Link: http://lkml.kernel.org/r/148545058784.17912.6353162518188733642.stgit@djiang5-desk3.ch.intel.comSigned-off-by: default avatarMatthew Wilcox <mawilcox@microsoft.com>
    Signed-off-by: default avatarDave Jiang <dave.jiang@intel.com>
    Signed-off-by: default avatarRoss Zwisler <ross.zwisler@linux.intel.com>
    Cc: Dave Hansen <dave.hansen@linux.intel.com>
    Cc: Vlastimil Babka <vbabka@suse.cz>
    Cc: Jan Kara <jack@suse.com>
    Cc: Dan Williams <dan.j.williams@intel.com>
    Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Cc: Nilesh Choudhury <nilesh.choudhury@oracle.com>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Dave Jiang <dave.jiang@intel.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    a2d58167
dax.c 40.3 KB