This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
Re: [PATCH][RFC] Allow explicit shrinking of arena heaps using anenvironment variable
On 21 July 2012 08:44, Rich Felker <dalias@aerifal.cx> wrote:
>> Based on the madvise man page (and also comments earlier in the
>> thread), MADV_DONTNEED also always[1] zeroes pages before subsequent
>> accesses to it, so isn't the page protection the only additional
>> action that the overlapping mmap provides? It shouldn't matter when
>> the pages get zeroed, since from the real user perspective, they're
>> zeroed pages.
>
> mprotect is not to prevent them from being accessed. It's to subtract
> them from the commit charge. Clean PROT_NONE pages do not contribute
> to commit charge. Writable pages do contribute to commit charge even
> if they're clean.
I'm sorry, but I still don't understand how setuid programs would
benefit from this, i.e. what is it about subtracting pages from the
commit charge that appeases the setuid-ness of the programs?
--
http://siddhesh.in