• Hugh Dickins's avatar
    ksm: get_ksm_page locked · 8aafa6a4
    Hugh Dickins authored
    In some places where get_ksm_page() is used, we need the page to be locked.
    
    When KSM migration is fully enabled, we shall want that to make sure that
    the page just acquired cannot be migrated beneath us (raised page count is
    only effective when there is serialization to make sure migration
    notices).  Whereas when navigating through the stable tree, we certainly
    do not want to lock each node (raised page count is enough to guarantee
    the memcmps, even if page is migrated to another node).
    
    Since we're about to add another use case, add the locked argument to
    get_ksm_page() now.
    
    Hmm, what's that rcu_read_lock() about?  Complete misunderstanding, I
    really got the wrong end of the stick on that!  There's a configuration in
    which page_cache_get_speculative() can do something cheaper than
    get_page_unless_zero(), relying on its caller's rcu_read_lock() to have
    disabled preemption for it.  There's no need for rcu_read_lock() around
    get_page_unless_zero() (and mapping checks) here.  Cut out that silliness
    before making this any harder to understand.
    Signed-off-by: default avatarHugh Dickins <hughd@google.com>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Petr Holasek <pholasek@redhat.com>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Izik Eidus <izik.eidus@ravellosystems.com>
    Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
    Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    8aafa6a4
ksm.c 57.5 KB