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-------- Original Message --------
Subject: Re: [PATCH] PSS(proportional set size) accounting in smaps
Date: Tue, 14 Aug 2007 10:56:12 +0530
From: Balbir Singh <[email protected]>
Reply-To: [email protected]
Organization: IBM
To: Andrew Morton <[email protected]>, Matt Mackall <[email protected]>, John Berthels <[email protected]>, linux-kernel <[email protected]>
References: <[email protected]>
Fengguang Wu wrote:
> The "proportional set size" (PSS) of a process is the count of pages it has in
> memory, where each page is divided by the number of processes sharing it. So if
> a process has 1000 pages all to itself, and 1000 shared with one other process,
> its PSS will be 1500.
> - lwn.net: "ELC: How much memory are applications really using?"
>
> The PSS proposed by Matt Mackall is a very nice metic for measuring an process's
> memory footprint. So collect and export it via /proc/<pid>/smaps.
>
> Matt Mackall's pagemap/kpagemap and John Berthels's exmap can also do the job,
> providing pretty much details. But for PSS, let's do it in a simple way.
>
> Cc: Matt Mackall <[email protected]>
> Cc: John Berthels <[email protected]>
> Signed-off-by: Fengguang Wu <[email protected]>
I like the idea of moving towards PSS. I had sent some patches back in December
last year
http://marc.info/?l=linux-mm&m=116738715329816&w=4
> ---
> fs/proc/task_mmu.c | 13 ++++++++++---
> 1 file changed, 10 insertions(+), 3 deletions(-)
>
> --- linux-2.6.23-rc2-mm2.orig/fs/proc/task_mmu.c
> +++ linux-2.6.23-rc2-mm2/fs/proc/task_mmu.c
> @@ -319,6 +319,7 @@ const struct file_operations proc_maps_o
> struct mem_size_stats
> {
> unsigned long resident;
> + u64 pss; /* proportional set size: my share of rss */
> unsigned long shared_clean;
> unsigned long shared_dirty;
> unsigned long private_clean;
> @@ -341,6 +342,7 @@ static int smaps_pte_range(pmd_t *pmd, u
> pte_t *pte, ptent;
> spinlock_t *ptl;
> struct page *page;
> + int mapcount;
>
> pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> for (; addr != end; pte++, addr += PAGE_SIZE) {
> @@ -357,16 +359,19 @@ static int smaps_pte_range(pmd_t *pmd, u
> /* Accumulate the size in pages that have been accessed. */
> if (pte_young(ptent) || PageReferenced(page))
> mss->referenced += PAGE_SIZE;
> - if (page_mapcount(page) >= 2) {
> + mapcount = page_mapcount(page);
> + if (mapcount >= 2) {
This accounting is of-course racy. Mapcount can change any moment.
> if (pte_dirty(ptent))
> mss->shared_dirty += PAGE_SIZE;
> else
> mss->shared_clean += PAGE_SIZE;
> + mss->pss += (PAGE_SIZE << 12) / mapcount;
> } else {
> if (pte_dirty(ptent))
> mss->private_dirty += PAGE_SIZE;
> else
> mss->private_clean += PAGE_SIZE;
> + mss->pss += (PAGE_SIZE << 12);
> }
> }
> pte_unmap_unlock(pte - 1, ptl);
> @@ -395,18 +400,20 @@ static int show_smap(struct seq_file *m,
> seq_printf(m,
> "Size: %8lu kB\n"
> "Rss: %8lu kB\n"
> + "Pss: %8lu kB\n"
> "Shared_Clean: %8lu kB\n"
> "Shared_Dirty: %8lu kB\n"
> "Private_Clean: %8lu kB\n"
> "Private_Dirty: %8lu kB\n"
> "Referenced: %8lu kB\n",
> (vma->vm_end - vma->vm_start) >> 10,
> - sarg.mss.resident >> 10,
> + sarg.mss.resident >> 10,
> + (unsigned long)(mss->pss >> 22),
> sarg.mss.shared_clean >> 10,
> sarg.mss.shared_dirty >> 10,
> sarg.mss.private_clean >> 10,
> sarg.mss.private_dirty >> 10,
> - sarg.mss.referenced >> 10);
> + sarg.mss.referenced >> 10);
>
> return ret;
> }
>
If we are reasonably sure that mapping will not change at the time
of page_rmap_xxxxx() operations, we could handle shared accounting
at those points and implement accurate shared accounting.
--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL
On Tue, Aug 14, 2007 at 10:57:31AM +0530, Balbir Singh wrote:
> I keep forgetting to check that you are on the cc. My email client
> loves dropping you from the to/cc list.
hehe, sorry for my crappy smtp server ;)
> Fengguang Wu wrote:
> > The "proportional set size" (PSS) of a process is the count of pages it has in
> > memory, where each page is divided by the number of processes sharing it. So if
> > a process has 1000 pages all to itself, and 1000 shared with one other process,
> > its PSS will be 1500.
> > - lwn.net: "ELC: How much memory are applications really using?"
> >
> > The PSS proposed by Matt Mackall is a very nice metic for measuring an process's
> > memory footprint. So collect and export it via /proc/<pid>/smaps.
> >
> > Matt Mackall's pagemap/kpagemap and John Berthels's exmap can also do the job,
> > providing pretty much details. But for PSS, let's do it in a simple way.
> >
> > Cc: Matt Mackall <[email protected]>
> > Cc: John Berthels <[email protected]>
> > Signed-off-by: Fengguang Wu <[email protected]>
>
> I like the idea of moving towards PSS. I had sent some patches back in December
> last year
>
> http://marc.info/?l=linux-mm&m=116738715329816&w=4
Thank you. That's a pretty comprehensive work.
> > - if (page_mapcount(page) >= 2) {
> > + mapcount = page_mapcount(page);
> > + if (mapcount >= 2) {
>
> This accounting is of-course racy. Mapcount can change any moment.
Sure it is: I never expect to provide accurate numbers.
The mapcount here is to prevent divide-by-zero errors.
> If we are reasonably sure that mapping will not change at the time
> of page_rmap_xxxxx() operations, we could handle shared accounting
> at those points and implement accurate shared accounting.
That would be desirable, if only we can keep the cost low ;)