Re: move-accounting-function-calls-out-of-critical-vm-code-paths.patch

Re: move-accounting-function-calls-out-of-critical-vm-code-paths.patch

[Christoph Lameter]

As requested by Andrew:

In the 2.6.11 development cycle function calls have been added to lots
of hot vm paths to do accounting. I think these should not go into the
final 2.6.1 release because these statistics can be collected in a different
way that does not require the updating of counters from frequently used
vm code paths and is consistent with the methods use elsewhere in the kernel
to obtain statistics.

These function calls are

acct_update_integrals	-> Account for processes based on stime changes
update_mem_hiwater	-> takes rss and total_vm hiwater marks.

acct_update_integrals is only useful to call if stime changes otherwise
it will simply return. It is therefore best to relocate the function call
to acct_update_integral into the function that updates stime which is
account_system_time and remove it from the vm code paths.

update_mem_hiwater finds the rss hiwater mark. RSS limits are checked in
account_system_time(). Thus is makes most sense to also move the function
call to update_mem_hiwater there. Otherwise a process may have a higher
rss hiwater mark than allowed by rss limits!

This means that the rss limit is not always updated if rss is increased
and thus not as accurate. But the benefit is that the rss checks do no
pollute the vm paths and that it is consistent with the rss limit check.

The following patch removes acct_update_integrals and update_mem_hiwater
from the hot vm paths. This patch is against 2.6.11-rc3.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.10/mm/mmap.c
=================================--- linux-2.6.10.orig/mm/mmap.c	2005-02-03 12:55:10.000000000 -0800
+++ linux-2.6.10/mm/mmap.c	2005-02-03 12:55:15.000000000 -0800
@@ -21,7 +21,6 @@
 #include <linux/hugetlb.h>
 #include <linux/profile.h>
 #include <linux/module.h>
-#include <linux/acct.h>
 #include <linux/mount.h>
 #include <linux/mempolicy.h>
 #include <linux/rmap.h>
@@ -1121,8 +1120,6 @@ out:
 					pgoff, flags & MAP_NONBLOCK);
 		down_write(&mm->mmap_sem);
 	}
-	acct_update_integrals();
-	update_mem_hiwater();
 	return addr;

 unmap_and_free_vma:
@@ -1463,8 +1460,6 @@ static int acct_stack_growth(struct vm_a
 	if (vma->vm_flags & VM_LOCKED)
 		mm->locked_vm += grow;
 	__vm_stat_account(mm, vma->vm_flags, vma->vm_file, grow);
-	acct_update_integrals();
-	update_mem_hiwater();
 	return 0;
 }

@@ -1970,8 +1965,6 @@ out:
 		mm->locked_vm += len >> PAGE_SHIFT;
 		make_pages_present(addr, addr + len);
 	}
-	acct_update_integrals();
-	update_mem_hiwater();
 	return addr;
 }

Index: linux-2.6.10/mm/mremap.c
=================================--- linux-2.6.10.orig/mm/mremap.c	2005-02-03 12:55:10.000000000 -0800
+++ linux-2.6.10/mm/mremap.c	2005-02-03 12:55:15.000000000 -0800
@@ -16,7 +16,6 @@
 #include <linux/fs.h>
 #include <linux/highmem.h>
 #include <linux/security.h>
-#include <linux/acct.h>
 #include <linux/syscalls.h>

 #include <asm/uaccess.h>
@@ -255,9 +254,6 @@ static unsigned long move_vma(struct vm_
 					   new_addr + new_len);
 	}

-	acct_update_integrals();
-	update_mem_hiwater();
-
 	return new_addr;
 }

@@ -394,8 +390,6 @@ unsigned long do_mremap(unsigned long ad
 				make_pages_present(addr + old_len,
 						   addr + new_len);
 			}
-			acct_update_integrals();
-			update_mem_hiwater();
 			ret = addr;
 			goto out;
 		}
Index: linux-2.6.10/mm/memory.c
=================================--- linux-2.6.10.orig/mm/memory.c	2005-02-03 12:55:10.000000000 -0800
+++ linux-2.6.10/mm/memory.c	2005-02-03 12:55:15.000000000 -0800
@@ -46,7 +46,6 @@
 #include <linux/highmem.h>
 #include <linux/pagemap.h>
 #include <linux/rmap.h>
-#include <linux/acct.h>
 #include <linux/module.h>
 #include <linux/init.h>

@@ -732,7 +731,6 @@ void zap_page_range(struct vm_area_struc
 	tlb = tlb_gather_mmu(mm, 0);
 	unmap_vmas(&tlb, mm, vma, address, end, &nr_accounted, details);
 	tlb_finish_mmu(tlb, address, end);
-	acct_update_integrals();
 	spin_unlock(&mm->page_table_lock);
 }

@@ -1334,11 +1332,9 @@ static int do_wp_page(struct mm_struct *
 	if (likely(pte_same(*page_table, pte))) {
 		if (PageAnon(old_page))
 			mm->anon_rss--;
-		if (PageReserved(old_page)) {
+		if (PageReserved(old_page))
 			++mm->rss;
-			acct_update_integrals();
-			update_mem_hiwater();
-		} else
+		else
 			page_remove_rmap(old_page);
 		break_cow(vma, new_page, address, page_table);
 		lru_cache_add_active(new_page);
@@ -1743,9 +1739,6 @@ static int do_swap_page(struct mm_struct
 		remove_exclusive_swap_page(page);

 	mm->rss++;
-	acct_update_integrals();
-	update_mem_hiwater();
-
 	pte = mk_pte(page, vma->vm_page_prot);
 	if (write_access && can_share_swap_page(page)) {
 		pte = maybe_mkwrite(pte_mkdirty(pte), vma);
@@ -1810,8 +1803,6 @@ do_anonymous_page(struct mm_struct *mm,
 			goto out;
 		}
 		mm->rss++;
-		acct_update_integrals();
-		update_mem_hiwater();
 		entry = maybe_mkwrite(pte_mkdirty(mk_pte(page,
 							 vma->vm_page_prot)),
 				      vma);
@@ -1928,8 +1919,6 @@ retry:
 	if (pte_none(*page_table)) {
 		if (!PageReserved(new_page))
 			++mm->rss;
-		acct_update_integrals();
-		update_mem_hiwater();

 		flush_icache_page(vma, new_page);
 		entry = mk_pte(new_page, vma->vm_page_prot);
@@ -2249,10 +2238,8 @@ EXPORT_SYMBOL(vmalloc_to_pfn);
  * update_mem_hiwater
  *	- update per process rss and vm high water data
  */
-void update_mem_hiwater(void)
+void update_mem_hiwater(struct task_struct *tsk)
 {
-	struct task_struct *tsk = current;
-
 	if (tsk->mm) {
 		if (tsk->mm->hiwater_rss < tsk->mm->rss)
 			tsk->mm->hiwater_rss = tsk->mm->rss;
Index: linux-2.6.10/mm/swapfile.c
=================================--- linux-2.6.10.orig/mm/swapfile.c	2005-02-03 12:55:10.000000000 -0800
+++ linux-2.6.10/mm/swapfile.c	2005-02-03 12:55:15.000000000 -0800
@@ -24,7 +24,6 @@
 #include <linux/module.h>
 #include <linux/rmap.h>
 #include <linux/security.h>
-#include <linux/acct.h>
 #include <linux/backing-dev.h>
 #include <linux/syscalls.h>

@@ -437,8 +436,6 @@ unuse_pte(struct vm_area_struct *vma, un
 	set_pte(dir, pte_mkold(mk_pte(page, vma->vm_page_prot)));
 	page_add_anon_rmap(page, vma, address);
 	swap_free(entry);
-	acct_update_integrals();
-	update_mem_hiwater();
 }

 /* vma->vm_mm->page_table_lock is held */
Index: linux-2.6.10/include/linux/mm.h
=================================--- linux-2.6.10.orig/include/linux/mm.h	2005-02-03 12:55:09.000000000 -0800
+++ linux-2.6.10/include/linux/mm.h	2005-02-03 12:55:15.000000000 -0800
@@ -836,7 +836,7 @@ static inline void vm_stat_unaccount(str
 }

 /* update per process rss and vm hiwater data */
-extern void update_mem_hiwater(void);
+extern void update_mem_hiwater(struct task_struct *tsk);

 #ifndef CONFIG_DEBUG_PAGEALLOC
 static inline void
Index: linux-2.6.10/mm/nommu.c
=================================--- linux-2.6.10.orig/mm/nommu.c	2005-02-03 12:55:10.000000000 -0800
+++ linux-2.6.10/mm/nommu.c	2005-02-03 12:55:15.000000000 -0800
@@ -955,10 +955,8 @@ void arch_unmap_area(struct vm_area_stru
 {
 }

-void update_mem_hiwater(void)
+void update_mem_hiwater(struct task_struct *tsk)
 {
-	struct task_struct *tsk = current;
-
 	if (likely(tsk->mm)) {
 		if (tsk->mm->hiwater_rss < tsk->mm->rss)
 			tsk->mm->hiwater_rss = tsk->mm->rss;
Index: linux-2.6.10/include/linux/acct.h
=================================--- linux-2.6.10.orig/include/linux/acct.h	2005-02-03 12:55:09.000000000 -0800
+++ linux-2.6.10/include/linux/acct.h	2005-02-03 12:55:15.000000000 -0800
@@ -120,12 +120,12 @@ struct acct_v3
 struct super_block;
 extern void acct_auto_close(struct super_block *sb);
 extern void acct_process(long exitcode);
-extern void acct_update_integrals(void);
+extern void acct_update_integrals(struct task_struct *tsk);
 extern void acct_clear_integrals(struct task_struct *tsk);
 #else
 #define acct_auto_close(x)	do { } while (0)
 #define acct_process(x)		do { } while (0)
-#define acct_update_integrals()		do { } while (0)
+#define acct_update_integrals(x)		do { } while (0)
 #define acct_clear_integrals(task)	do { } while (0)
 #endif

Index: linux-2.6.10/kernel/acct.c
=================================--- linux-2.6.10.orig/kernel/acct.c	2005-02-03 12:55:10.000000000 -0800
+++ linux-2.6.10/kernel/acct.c	2005-02-03 12:55:15.000000000 -0800
@@ -534,10 +534,8 @@ void acct_process(long exitcode)
  * acct_update_integrals
  *    -  update mm integral fields in task_struct
  */
-void acct_update_integrals(void)
+void acct_update_integrals(struct task_struct *tsk)
 {
-	struct task_struct *tsk = current;
-
 	if (likely(tsk->mm)) {
 		long delta = tsk->stime - tsk->acct_stimexpd;

Index: linux-2.6.10/kernel/sched.c
=================================--- linux-2.6.10.orig/kernel/sched.c	2005-02-03 12:55:10.000000000 -0800
+++ linux-2.6.10/kernel/sched.c	2005-02-03 12:55:15.000000000 -0800
@@ -45,6 +45,7 @@
 #include <linux/seq_file.h>
 #include <linux/syscalls.h>
 #include <linux/times.h>
+#include <linux/acct.h>
 #include <asm/tlb.h>

 #include <asm/unistd.h>
@@ -2373,6 +2374,10 @@ void account_system_time(struct task_str
 		cpustat->iowait = cputime64_add(cpustat->iowait, tmp);
 	else
 		cpustat->idle = cputime64_add(cpustat->idle, tmp);
+	/* Account for system time used */
+	acct_update_integrals(p);
+	/* Update rss highwater mark */
+	update_mem_hiwater(p);
 }

 /*
Index: linux-2.6.10/mm/rmap.c
=================================--- linux-2.6.10.orig/mm/rmap.c	2005-02-03 12:55:10.000000000 -0800
+++ linux-2.6.10/mm/rmap.c	2005-02-03 12:55:15.000000000 -0800
@@ -51,7 +51,6 @@
 #include <linux/swapops.h>
 #include <linux/slab.h>
 #include <linux/init.h>
-#include <linux/acct.h>
 #include <linux/rmap.h>
 #include <linux/rcupdate.h>

@@ -600,7 +599,6 @@ static int try_to_unmap_one(struct page
 	}

 	mm->rss--;
-	acct_update_integrals();
 	page_remove_rmap(page);
 	page_cache_release(page);

@@ -705,7 +703,6 @@ static void try_to_unmap_cluster(unsigne

 		page_remove_rmap(page);
 		page_cache_release(page);
-		acct_update_integrals();
 		mm->rss--;
 		(*mapcount)--;
 	}
Index: linux-2.6.10/fs/exec.c
=================================--- linux-2.6.10.orig/fs/exec.c	2005-02-03 12:55:08.000000000 -0800
+++ linux-2.6.10/fs/exec.c	2005-02-03 13:02:37.000000000 -0800
@@ -1191,8 +1191,6 @@ int do_execve(char * filename,

 		/* execve success */
 		security_bprm_free(bprm);
-		acct_update_integrals();
-		update_mem_hiwater();
 		kfree(bprm);
 		return retval;
 	}
Index: linux-2.6.10/kernel/exit.c
=================================--- linux-2.6.10.orig/kernel/exit.c	2005-02-03 12:55:10.000000000 -0800
+++ linux-2.6.10/kernel/exit.c	2005-02-03 12:55:15.000000000 -0800
@@ -806,8 +806,8 @@ fastcall NORET_TYPE void do_exit(long co
 				current->comm, current->pid,
 				preempt_count());

-	acct_update_integrals();
-	update_mem_hiwater();
+	acct_update_integrals(tsk);
+	update_mem_hiwater(tsk);
 	group_dead = atomic_dec_and_test(&tsk->signal->live);
 	if (group_dead)
 		acct_process(code);

Re: move-accounting-function-calls-out-of-critical-vm-code-paths.patch

[Christoph Lameter]

On Thu, 3 Feb 2005, Andrew Morton wrote:

> Has any performance testing been done?

Jay did some performance testing and found minor performance increases
without my page fault patches. But then the performance without the page
fault patches is already so bad due to the page_table_lock
contention that this is not so important.

> > acct_update_integrals is only useful to call if stime changes otherwise
> > it will simply return. It is therefore best to relocate the function call
> > to acct_update_integral into the function that updates stime which is
> > account_system_time and remove it from the vm code paths.
>
> But that changes (breaks) the semantics significantly.  A task will now
> only have its BSD accounting fields updated when it happens to be
> interrupted by the timer.  Some tasks:
>
> 	for ( ; ; ) {
> 		nanosleep(2 milliseconds);
> 		do_stuff_for(0.5 milliseconds);
> 	}
>
> will see their BSD accounting fields remaining stuck firmly at zero.
>
> I think?

Accounting is only effective is stime changes even with the current
code. If the process never gets its stime increased then also the
accounting does nothing. There is no change in that behavior.

> > update_mem_hiwater finds the rss hiwater mark. RSS limits are checked in
> > account_system_time().
>
> Linux doesn't check rss limits anywhere.  We check CPU usage in
> account_system_time().

Yuck. I was mistaken in what check_rlimit does.

> Most of this could be fixed up by updating these counters at schedule()
> time as well, although that would become somewhat inaccurate if we later
> decide to implement rss enforcement at pagefault time.

Right. I hope that Roland's changes for higher resolution of cputime would
make that possible. But this is Jay's thing not mine. I just want to make
sure that the CSA patches does not get in the way of our attempts to
improve the performance of the page fault handler. In the discussions on
linux-mm there was also some concern about adding these calls.

Re: move-accounting-function-calls-out-of-critical-vm-code-paths.patch

[Tim Schmielau]

On Thu, 3 Feb 2005, Andrew Morton wrote:

> Well your patch certainly cleans things up in there and would be a good
> thing to have as long as we can be sure that it doesn't break the
> accounting in some subtle way.

I think it also fits well with the other accounting data which is only 
statistically probed at clock ticks.

> Which implies that we need to see some additional accounting code, so we
> can verify that the base accumulation infrastructure is doing the expected
> thing.  As well as an ack from the interested parties.  Does anyone know
> what's happening with all the new accounting initiatives?  I'm seeing no
> activity at all.

Well, I'm here :), but I'm concentrating on making a GNU acct release 
happen.
Anyways, as I'm not involved with memory accounting yet, I guess I should 
leave it to CSA and ELSA people to comment.

Tim

Re: move-accounting-function-calls-out-of-critical-vm-code-paths.patch

[Jay Lan]

Andrew Morton wrote:
> Christoph Lameter <clameter@sgi.com> wrote:
> 
>>I hope that Roland's changes for higher resolution of cputime would
>>make that possible. But this is Jay's thing not mine. I just want to make
>>sure that the CSA patches does not get in the way of our attempts to
>>improve the performance of the page fault handler. In the discussions on
>>linux-mm there was also some concern about adding these calls.
> 
> 
> Well your patch certainly cleans things up in there and would be a good
> thing to have as long as we can be sure that it doesn't break the
> accounting in some subtle way.
> 
> Which implies that we need to see some additional accounting code, so we
> can verify that the base accumulation infrastructure is doing the expected
> thing.  As well as an ack from the interested parties.  Does anyone know
> what's happening with all the new accounting initiatives?  I'm seeing no
> activity at all.

Sorry guys! I have been away for three weeks on short term disability.:(

I have tested Christoph's patch before the leave. It did work for CSA
and showed performance improvement on certain configuration.

CSA is currently implemented as a loadable module. I think ELSA is the
same, right? The use of the enhanced accounting data collection
code is not in the kernel tree. That was why Andrew did not see usage of 
the accounting patches. Should i propose to include the CSA module in
the kernel then, Andrew? :)

Cheers,
  - jay