Re: /proc/*/statm, exactly what does "shared" mean?

[Mauricio Lin <mauriciolin@gmail.com>]

Hi all,

Sorry for responding this email so late. I was busy with my trip.

On Sat, 12 Feb 2005 15:42:15 +0000 (GMT), Hugh Dickins <hugh@veritas.com> wrote:
> On Sat, 12 Feb 2005, Richard F. Rebel wrote:
> >
> > That said, many mod_perl users are *VERY* interested in being able to
> > detect and observe how "shared" our forked children are.  Shared meaning
> > private pages shared with children (copy on write).  Is it even possible
> > to do this in 2.6 kernels?  If so, any pointers would be very helpful.
> 
> Not in any of the vanilla kernels.
> 
> Mauricio has a /proc/<pid>/smaps patch, in which he returns to looking
> at every pte slot of every vma of the process as /proc/<pid>/statm did
> in 2.4.  I suggest you ask him offline for his latest version (the last
> I saw did not include support for 2.6.11's pud level; 
I put the pud level on the last patch I sent to the linux-kernel list
as suggested by Marcelo Tosatti.

> and looped in an
> inefficient way, repeatedly locating, mapping and unmapping the page
> table for each pte slot - needs refactoring into pgd_range, pud_range,
> pmd_range, pte_range levels like 2.4's statm).
Well, for each vma it is checked how many pages are mapped to rss. So
I have to check per page if it is allocated in physical memory. I know
that this is a heavy function, but do you have any suggestion to
improve this?  What do you mean "needs refactoring into pgd_range,
pud_range, pmd_range, pte_range levels like 2.4's statm"? Could you
give more details, please?

BR,

Mauricio Lin.