• Eric B Munson's avatar
    hugetlbfs: allow the creation of files suitable for MAP_PRIVATE on the vfs internal mount · 6bfde05b
    Eric B Munson authored
    This patchset adds a flag to mmap that allows the user to request that an
    anonymous mapping be backed with huge pages.  This mapping will borrow
    functionality from the huge page shm code to create a file on the kernel
    internal mount and use it to approximate an anonymous mapping.  The
    MAP_HUGETLB flag is a modifier to MAP_ANONYMOUS and will not work without
    both flags being preset.
    
    A new flag is necessary because there is no other way to hook into huge
    pages without creating a file on a hugetlbfs mount which wouldn't be
    MAP_ANONYMOUS.
    
    To userspace, this mapping will behave just like an anonymous mapping
    because the file is not accessible outside of the kernel.
    
    This patchset is meant to simplify the programming model.  Presently there
    is a large chunk of boiler platecode, contained in libhugetlbfs, required
    to create private, hugepage backed mappings.  This patch set would allow
    use of hugepages without linking to libhugetlbfs or having hugetblfs
    mounted.
    
    Unification of the VM code would provide these same benefits, but it has
    been resisted each time that it has been suggested for several reasons: it
    would break PAGE_SIZE assumptions across the kernel, it makes page-table
    abstractions really expensive, and it does not provide any benefit on
    architectures that do not support huge pages, incurring fast path
    penalties without providing any benefit on these architectures.
    
    This patch:
    
    There are two means of creating mappings backed by huge pages:
    
            1. mmap() a file created on hugetlbfs
            2. Use shm which creates a file on an internal mount which essentially
               maps it MAP_SHARED
    
    The internal mount is only used for shared mappings but there is very
    little that stops it being used for private mappings. This patch extends
    hugetlbfs_file_setup() to deal with the creation of files that will be
    mapped MAP_PRIVATE on the internal hugetlbfs mount. This extended API is
    used in a subsequent patch to implement the MAP_HUGETLB mmap() flag.
    Signed-off-by: default avatarEric Munson <ebmunson@us.ibm.com>
    Acked-by: default avatarDavid Rientjes <rientjes@google.com>
    Cc: Mel Gorman <mel@csn.ul.ie>
    Cc: Adam Litke <agl@us.ibm.com>
    Cc: David Gibson <david@gibson.dropbear.id.au>
    Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
    Cc: Nick Piggin <nickpiggin@yahoo.com.au>
    Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    6bfde05b
hugetlb.h 8.52 KB