• Matthew Wilcox's avatar
    mm: allow page fault handlers to perform the COW · 2e4cdab0
    Matthew Wilcox authored
    Currently COW of an XIP file is done by first bringing in a read-only
    mapping, then retrying the fault and copying the page.  It is much more
    efficient to tell the fault handler that a COW is being attempted (by
    passing in the pre-allocated page in the vm_fault structure), and allow
    the handler to perform the COW operation itself.
    
    The handler cannot insert the page itself if there is already a read-only
    mapping at that address, so allow the handler to return VM_FAULT_LOCKED
    and set the fault_page to be NULL.  This indicates to the MM code that the
    i_mmap_lock is held instead of the page lock.
    Signed-off-by: default avatarMatthew Wilcox <matthew.r.wilcox@intel.com>
    Acked-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Cc: Andreas Dilger <andreas.dilger@intel.com>
    Cc: Boaz Harrosh <boaz@plexistor.com>
    Cc: Christoph Hellwig <hch@lst.de>
    Cc: Dave Chinner <david@fromorbit.com>
    Cc: Jan Kara <jack@suse.cz>
    Cc: Jens Axboe <axboe@kernel.dk>
    Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
    Cc: Randy Dunlap <rdunlap@infradead.org>
    Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
    Cc: Theodore Ts'o <tytso@mit.edu>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    2e4cdab0
mm.h 71.3 KB