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    SubjectRe: [PATCH] proc: put check_mem_permission before __get_free_page in mem_read
    On Tue, Apr 26, 2011 at 11:56 AM, Hugh Dickins <> wrote:
    > On Sun, 17 Apr 2011, wrote:
    >> From: Jovi Zhang <>
    >> 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 <>
    > 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.
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