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DateThu, 28 Jun 2007 23:04:10 -0400
FromRik van Riel <>
SubjectRe: [patch 0/4] MAP_NOZERO v2 - VM_NOZERO/MAP_NOZERO early summer madness
Kyle Moffett wrote:
> On Jun 28, 2007, at 14:49:24, Davide Libenzi wrote:
>> I was using oprofile to sample some userspace code I am working on, 
>> and I was continuosly noticing  clear_page  in the top three entries 
>> of the oprofile logs.>>>> Also, a simple kernel build, in my Dual Opteron with 8GB of RAM, 
>> shows  clear_page  as the first kernel entry, second only to the 
>> userspace the  cc1  and  as. Most of the userspace code uses malloc() 
>> (and anonymous  mappings) in such a way that the memory returned via 
>> kernel->glibc is immediately written soon after. The POSIX malloc() 
>> definition itself also, does not require the returned memory to be 
>> zeroed (as calloc() does).>>>> So I implemented a rather quick hack that introduces a new mmap() flag 
>> MAP_NOZERO (only valid for anonymous mappings) and the  vma  
>> counter-part VM_NOZERO. Also, a new sys_brk2() has been introduced to 
>> accept a new flags  parameter. A brief description of the patches 
>> follows in the next emails.> > Hmm, sounds like this would also need a "MAP_NOREUSE" flag of some kind 
> for security sensitive applications.

That wants MAP_PRIVATE so that the kernel can also decide to not
swap these pages out to an unencrypted swap area.

-- 
Politics is the struggle between those who want to make their country
the best in the world, and those who believe it already is.  Each group
calls the other unpatriotic.
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