lkml.org 
[lkml]   [2011]   [Apr]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    SubjectRe: [PATCH] proc: put check_mem_permission before __get_free_page in mem_read
    From
    On Tue, Apr 26, 2011 at 11:56 AM, Hugh Dickins <hughd@google.com> wrote:
    > On Sun, 17 Apr 2011, bookjovi@gmail.com wrote:
    >> From: Jovi Zhang <bookjovi@gmail.com>
    >>
    >> It should be better if put check_mem_permission before __get_free_page
    >> in mem_read, to be same as function mem_write.
    >>
    >> Signed-off-by: Jovi Zhang <bookjovi@gmail.com>
    >
    > Sorry to be contrary, but I disagree with this.  I'm all for consistency,
    > but is there a particular reason why you think the mem_write ordering is
    > right and mem_read wrong?
    >
    > My reason for preferring the current mem_read ordering is this:
    >
    > check_mem_permission gets a reference to the mm.  If we __get_free_page
    > after check_mem_permission, imagine what happens if the system is out
    > of memory, and the mm we're looking at is selected for killing by the
    > OOM killer: while we wait in __get_free_page for more memory, no memory
    > is freed from the selected mm because it cannot reach exit_mmap while
    > we hold that reference.
    >
    > (I may be overstating the case: a little memory may be freed from the
    > exiting task's stack, and kswapd should still be able to pick some pages
    > off the mm.  But nonetheless, we would do better to let this mm go.)
    >

    Indeed, I missed that point. Thanks.
    --
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2011-04-26 10:57    [W:0.033 / U:88.684 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site