Re: [9fans] [Fwd: [olpc-software] Multi-protection VMAs and memory usage]

["David Leimbach" <leimy2k@gmail.com>]

I love the Video Music Awards too...  and all other 3 letter acronyms

On 5/12/06, Ronald G Minnich <rminnich@lanl.gov> wrote:
> Just got this from the OLPC list. Another reason to love shared
> libaries. Are things getting kludgy here or what ...
>
>
> =====
> LWN lwn.net had an article this week discussing a patch that can
> result is some nice memory savings for 'multi-protection VMAs'
>
> Here is a link the relevant kernel mailing list thread
>
> http://thread.gmane.org/gmane.linux.kernel/402675
>
> and here is an excerpt from the lwn article,
>
> "Ordinary Linux users could also benefit from this patch, however.
> Ulrich Drepper explained how the C library uses VMAs currently; it
> turns out that linking to a single shared library can create up to
> five separate VMAs. An application which brings in a large number of
> libraries - as many desktop applications do - can end up creating
> hundreds of VMAs for shared library mappings. That leads to many VMAs
> being created on the system; just how many can be seen by looking at
> the vm_area_struct line in /proc/slabinfo. Your editor's system
> currently has over 13,000 VMAs active, using about 2.5MB of memory.
>
> Of the five VMAs potentially created by glibc for each shared library
> mapping, four are mappings into the same file with different
> permissions. The ability to have multiple permissions settings within
> a single VMA has the potential to collapse those four VMAs into one,
> leaving a single file mapping and an anonymous memory segment for each
> library. The result would be significantly reduced memory usage and
> faster kernel performance. Those benefits are likely to motivate the
> inclusion of this patch, sooner or later. "
>
>