[PATCH] accounting per process swapped out pages

[PATCH] accounting per process swapped out pages

[Mulyadi Santosa]

Hello everyone.

Here is patch to count per process swapped out pages. This patch is 
created against 2.6.16.1. So far, I had tested by forcing certain task 
to swap out (tail -f /dev/zero) and wait until top/vmstat/free reported
that swap is occupied.

Comments and feedbacks are  greatly appreciated. Please keep me CC'ed 
since I am not subscribed to linux-kernel mailing list.

regards,

Mulyadi


# diffstat ./swap-acct.patch
 fs/proc/task_mmu.c |   14 ++++++++++++--
 include/linux/mm.h |    1 +
 mm/memory.c        |    3 +++
 mm/rmap.c          |    1 +
 mm/swapfile.c      |    1 +
5 files changed, 18 insertions(+), 2 deletions(-)

--- fs/proc/task_mmu.c.bak	2006-03-28 13:49:02.000000000 +0700
+++ fs/proc/task_mmu.c	2006-07-22 19:18:33.000000000 +0700
@@ -15,6 +15,8 @@ char *task_mem(struct mm_struct *mm, cha
 {
 	unsigned long data, text, lib;
 	unsigned long hiwater_vm, total_vm, hiwater_rss, total_rss;
+	struct vm_area_struct * this_vma;
+	unsigned long swp_out_pages=0;
 
 	/*
 	 * Note: to minimize their overhead, mm maintains hiwater_vm and
@@ -33,6 +35,12 @@ char *task_mem(struct mm_struct *mm, cha
 	data = mm->total_vm - mm->shared_vm - mm->stack_vm;
 	text = (PAGE_ALIGN(mm->end_code) - (mm->start_code & PAGE_MASK)) >> 10;
 	lib = (mm->exec_vm << (PAGE_SHIFT-10)) - text;
+
+	for(this_vma = mm->mmap;this_vma;this_vma = this_vma->vm_next)
+	{
+		swp_out_pages += atomic_read(&(this_vma)->swapped_out);
+	}
+
 	buffer += sprintf(buffer,
 		"VmPeak:\t%8lu kB\n"
 		"VmSize:\t%8lu kB\n"
@@ -43,7 +51,8 @@ char *task_mem(struct mm_struct *mm, cha
 		"VmStk:\t%8lu kB\n"
 		"VmExe:\t%8lu kB\n"
 		"VmLib:\t%8lu kB\n"
-		"VmPTE:\t%8lu kB\n",
+		"VmPTE:\t%8lu kB\n"
+		"VmSwp:\t%8lu kB\n",
 		hiwater_vm << (PAGE_SHIFT-10),
 		(total_vm - mm->reserved_vm) << (PAGE_SHIFT-10),
 		mm->locked_vm << (PAGE_SHIFT-10),
@@ -51,7 +60,8 @@ char *task_mem(struct mm_struct *mm, cha
 		total_rss << (PAGE_SHIFT-10),
 		data << (PAGE_SHIFT-10),
 		mm->stack_vm << (PAGE_SHIFT-10), text, lib,
-		(PTRS_PER_PTE*sizeof(pte_t)*mm->nr_ptes) >> 10);
+		(PTRS_PER_PTE*sizeof(pte_t)*mm->nr_ptes) >> 10,
+		swp_out_pages << (PAGE_SHIFT-10) );
 	return buffer;
 }
 
--- include/linux/mm.h.bak	2006-03-28 13:49:02.000000000 +0700
+++ include/linux/mm.h	2006-07-22 19:20:34.000000000 +0700
@@ -111,6 +111,7 @@ struct vm_area_struct {
 #ifdef CONFIG_NUMA
 	struct mempolicy *vm_policy;	/* NUMA policy for the VMA */
 #endif
+	atomic_t  swapped_out;	/* swapped out pages in this VMA */
 };
 
 /*
--- mm/rmap.c.bak	2006-03-28 13:49:02.000000000 +0700
+++ mm/rmap.c	2006-07-22 19:19:47.000000000 +0700
@@ -635,6 +635,7 @@ static int try_to_unmap_one(struct page 
 		set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
 		BUG_ON(pte_file(*pte));
 		dec_mm_counter(mm, anon_rss);
+		atomic_inc(&(vma)->swapped_out);
 	} else
 		dec_mm_counter(mm, file_rss);
 
--- mm/memory.c.bak	2006-03-28 13:49:02.000000000 +0700
+++ mm/memory.c	2006-07-25 16:04:42.000000000 +0700
@@ -683,6 +683,7 @@ static unsigned long zap_pte_range(struc
 	} while (pte++, addr += PAGE_SIZE, (addr != end && *zap_work > 0));
 
 	add_mm_rss(mm, file_rss, anon_rss);
+	atomic_sub(anon_rss,&(vma)->swapped_out);
 	pte_unmap_unlock(pte - 1, ptl);
 
 	return addr;
@@ -1928,6 +1929,8 @@ again:
 	/* The page isn't present yet, go ahead with the fault. */
 
 	inc_mm_counter(mm, anon_rss);
+	printk("Reducing swapped_out variable...\n");
+	atomic_dec(&(vma)->swapped_out);
 	pte = mk_pte(page, vma->vm_page_prot);
 	if (write_access && can_share_swap_page(page)) {
 		pte = maybe_mkwrite(pte_mkdirty(pte), vma);
--- mm/swapfile.c.bak	2006-07-25 18:25:57.000000000 +0700
+++ mm/swapfile.c	2006-07-25 18:43:17.000000000 +0700
@@ -426,6 +426,7 @@ static void unuse_pte(struct vm_area_str
 		unsigned long addr, swp_entry_t entry, struct page *page)
 {
 	inc_mm_counter(vma->vm_mm, anon_rss);
+	atomic_dec(&(vma)->swapped_out);
 	get_page(page);
 	set_pte_at(vma->vm_mm, addr, pte,
 		   pte_mkold(mk_pte(page, vma->vm_page_prot)));

Re: [PATCH] accounting per process swapped out pages

[Hugh Dickins]

On Fri, 4 Aug 2006, Mulyadi Santosa wrote:
> 
> Here is patch to count per process swapped out pages. This patch is 
> created against 2.6.16.1. So far, I had tested by forcing certain task 
> to swap out (tail -f /dev/zero) and wait until top/vmstat/free reported
> that swap is occupied.
> 
> Comments and feedbacks are  greatly appreciated. Please keep me CC'ed 
> since I am not subscribed to linux-kernel mailing list.

To be honest, I don't think there's much interest in this particular
VmSwp statistic; and if there's little interest in it, we'd rather
not spend the time and space on collecting it.  But I could be wrong:
let's see who speaks up for it.

A few comments on the mechanics of your patch.

You waste space in every vm_area_struct for your swapped_out count,
then /proc/<pid>/status has to loop over the vmas adding them up.
Much better to make it an mm_counter like anon_rss, then you only
use space in mm_struct, and don't have to add them up at the end,
and avoid dirtying (vma) cachelines unnecessarily, and (in some
cases) avoid the atomic operations.

While you've caught the main places where you'd need to adjust
swapped_out, you've missed a couple (maybe I've missed more):
copy_pte_range (fork) needs to increment the count, zap_pte_range
(munmap or truncate or exit) needs to decrement it.  Check wherever
anon_rss is adjusted, some not all would need swapped_out adjusted.

Oh, you are doing something in zap_pte_range, but I'm sorry to say
what you do there is nonsense: the number you're subtracting has
nothing to do with the number of swapped out pages.

And you probably wouldn't want that printk in your final patch!

Hugh

Re: [PATCH] accounting per process swapped out pages

[Mulyadi Santosa]

Hi ...

> To be honest, I don't think there's much interest in this particular
> VmSwp statistic; and if there's little interest in it, we'd rather
> not spend the time and space on collecting it.  But I could be wrong:
> let's see who speaks up for it.

I got the same impression too, but I do think this statistic is 
important if someone wants to know which program suffers most when 
(heavy) swapping happens. Some programs like "top" would also get 
benefit since  its "swapped" accounting is just based on virtual-rss, 
which is wrong (just showing parts that haven't been brought to RAM)

> You waste space in every vm_area_struct for your swapped_out count,
> then /proc/<pid>/status has to loop over the vmas adding them up.
> Much better to make it an mm_counter like anon_rss, then you only
> use space in mm_struct, and don't have to add them up at the end,
> and avoid dirtying (vma) cachelines unnecessarily, and (in some
> cases) avoid the atomic operations.

Let's see if I can adapt this idea. Actually, in the first place, I was 
thinking this way but sometimes it is easier to get pointer to 
vm_area_struct rather than to mm_struct. I'll take a deeper look...

Avoiding atomic operation is also my another primary target....

> While you've caught the main places where you'd need to adjust
> swapped_out, you've missed a couple (maybe I've missed more):
> copy_pte_range (fork) needs to increment the count, zap_pte_range
> (munmap or truncate or exit) needs to decrement it.  Check wherever
> anon_rss is adjusted, some not all would need swapped_out adjusted.

Yes, I use anon_rss a the "guidance" on where I probably put the 
swapped_out accounting and decide whether it  actually has anything to 
do with swapping or not. Hmmmm, looks like I still miss a lot...

> Oh, you are doing something in zap_pte_range, but I'm sorry to say
> what you do there is nonsense: the number you're subtracting has
> nothing to do with the number of swapped out pages.

:( OK, re-checking...

> And you probably wouldn't want that printk in your final patch!

Perfect closing, i forgot to clean that printk(). Thanks for reminding 
me...

Refined patch will follow ASAP..

regards,

Mulyadi