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

[Mauricio Lin <mauriciolin@gmail.com>]

Hi Hugh,

Thanks by your suggestion. I did not know that kernel 2.4.29 has
changed the statm implementation. As I can see the statm
implementation is different between 2.4 and 2.6.

Let me see if I can use the 2.4.29 statm idea to improve the smaps for
kernel 2.6.11-rc.

BR,

Mauricio Lin.

On Wed, 16 Feb 2005 12:00:55 +0000 (GMT), Hugh Dickins <hugh@veritas.com> wrote:
> On Wed, 16 Feb 2005, Mauricio Lin wrote:
> > 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?
> 
> Just look at, say, linux-2.4.29/fs/proc/array.c proc_pid_statm:
> which calls statm_pgd_range which calls statm_pmd_range which
> calls statm_pte_range which scans along the array of ptes doing
> the pte examination you're doing.  There are plenty of examples
> in 2.6.11-rc mm/memory.c of how to do it with pud level too.
> 
> Whereas your way starts at the top and descends the tree each time
> for every leaf, repeatedly mapping and unmapping the page table if
> that pagetable is in highmem.  You took follow_page as your starting
> point, which is good for a single pte, but inefficient for many.
> 
> Your function(s) will still be heavyweight, but somewhat faster.
> 
> Hugh
>