[lkml]   [2011]   [Apr]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
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.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2011-04-26 10:57    [W:0.094 / U:40.052 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site