Re: [PATCH] recognize MAP_LOCKED in mmap() call

Re: [PATCH] recognize MAP_LOCKED in mmap() call

[Mark_H_Johnson]

>This is what the manpage says...
>
>       mlockall  disables  paging  for  all pages mapped into the
>       address space of the calling process.  This  includes  the
>       pages  of  the  code,  data  and stack segment, as well as
>       shared libraries, user space kernel  data,  shared  memory
>       and  memory  mapped files. All mapped pages are guaranteed
>       to be resident  in  RAM  when  the  mlockall  system  call
>       returns  successfully  and  they are guaranteed to stay in
>       RAM until the pages  are  unlocked  again  by  munlock  or
>       munlockall  or  until  the  process  terminates  or starts
>       another program with exec.  Child processes do not inherit
>       page locks across a fork.
>
>Do you read that all pages must be faulted in apriori ?
>Or is it sufficient to to make sure none of the currently mapped
>pages are swapped out and future swapout is prohibited.
>
The key phrase is that "...all mapped pages are guaranteed to be resident
in RAM when the mlockall system call returns successfully..." (third
sentence) In that way I would expect the segments containing the code,
heap, and current stack allocations to be resident. I do not expect
the full stack allocation (e.g., 2M for each thread if that is the
stack size) to be mapped (nor resident) unless I take special action
to grow the stack that large.

We happen to have special code to grow each stack and allocate heap
variables to account for what we expect to use prior to mlockall.

That does raise a question though - are there other segments (e.g.,
debug information) that may be in the total size calculations that
are mapped only when some special action is taken (e.g., I run the
debugger)? That would explain the difference - the measures I reported
on were with executables built with debug symbols.

That might also explain a possible problem we have had when trying
to debug such an application after an hour of run time or so. If
running gdb triggers a growth in locked memory (and we don't have
enough) - we would likely get an error condition that isn't normally
expected by gdb.

>This still allows for page faults on pages that have not been
>mapped in the specified range or process. If required the
>app could touch these and they wouldn't be swapped later.
>

I don't think touching the pages is enough - they have to be allocated
and the maps generated (e.g., calls to mmap, malloc). That is a possibly
expensive operation when real time is active and something we try to
avoid whenever possible.

--
--Mark H Johnson
  <mailto:Mark_H_Johnson@raytheon.com>

Re: [PATCH] recognize MAP_LOCKED in mmap() call

[Mark_H_Johnson]

Andrew Morton wrote:
>(SuS really only anticipates that mmap needs to look at prior mlocks
>in force against the address range.  It also says
>
>     Process memory locking does apply to shared memory regions,
>
>and we don't do that either.  I think we should; can't see why SuS
>requires this.)

Let me make sure I read what you said correctly. Does this mean that Linux
2.4 (or 2.5) kernels do not lock shared memory regions if a process uses
mlockall?

If not, that is *really bad* for our real time applications. We don't want
to take a page fault while running some 80hz task, just because some
non-real time application tried to use what little physical memory we allow
for the kernel and all other applications.

I asked a related question about a week ago on linux-mm and didn't get a
response. Basically, I was concerned that top did not show RSS == Size when
mlockall(MCL_CURRENT|MCL_FUTURE) was called. Could this explain the
difference or is there something else that I'm missing here?

Thanks.
--Mark H Johnson
  <mailto:Mark_H_Johnson@raytheon.com>

Re: [PATCH] recognize MAP_LOCKED in mmap() call

[Rik van Riel]

On Wed, 18 Sep 2002 Mark_H_Johnson@raytheon.com wrote:
> Andrew Morton wrote:
> >(SuS really only anticipates that mmap needs to look at prior mlocks
> >in force against the address range.  It also says
> >
> >     Process memory locking does apply to shared memory regions,
> >
> >and we don't do that either.  I think we should; can't see why SuS
> >requires this.)
>
> Let me make sure I read what you said correctly. Does this mean that
> Linux 2.4 (or 2.5) kernels do not lock shared memory regions if a
> process uses mlockall?

But it does.  Linux won't evict memory that's MLOCKed...

cheers,

Rik
-- 
Spamtrap of the month: september@surriel.com

http://www.surriel.com/		http://distro.conectiva.com/

Re: [PATCH] recognize MAP_LOCKED in mmap() call

[Andrew Morton]

Mark_H_Johnson@raytheon.com wrote:
> 
> Andrew Morton wrote:
> >(SuS really only anticipates that mmap needs to look at prior mlocks
> >in force against the address range.  It also says
> >
> >     Process memory locking does apply to shared memory regions,
> >
> >and we don't do that either.  I think we should; can't see why SuS
> >requires this.)
> 
> Let me make sure I read what you said correctly. Does this mean that Linux
> 2.4 (or 2.5) kernels do not lock shared memory regions if a process uses
> mlockall?

Linux does lock these regions.  SuS seems to imply that we shouldn't.
But we should.

> If not, that is *really bad* for our real time applications. We don't want
> to take a page fault while running some 80hz task, just because some
> non-real time application tried to use what little physical memory we allow
> for the kernel and all other applications.
> 
> I asked a related question about a week ago on linux-mm and didn't get a
> response. Basically, I was concerned that top did not show RSS == Size when
> mlockall(MCL_CURRENT|MCL_FUTURE) was called. Could this explain the
> difference or is there something else that I'm missing here?
> 

That mlockall should have faulted everything in.  It could be an
accounting bug, or it could be a bug.  That's not an aspect which
gets tested a lot.  I'll take a look.

Re: [PATCH] recognize MAP_LOCKED in mmap() call

[Hubertus Franke]

On Wednesday 18 September 2002 03:54 pm, Andrew Morton wrote:
> Mark_H_Johnson@raytheon.com wrote:
> > Andrew Morton wrote:
> > >(SuS really only anticipates that mmap needs to look at prior mlocks
> > >in force against the address range.  It also says
> > >
> > >     Process memory locking does apply to shared memory regions,
> > >
> > >and we don't do that either.  I think we should; can't see why SuS
> > >requires this.)
> >
> > Let me make sure I read what you said correctly. Does this mean that
> > Linux 2.4 (or 2.5) kernels do not lock shared memory regions if a process
> > uses mlockall?
>
> Linux does lock these regions.  SuS seems to imply that we shouldn't.
> But we should.
>
> > If not, that is *really bad* for our real time applications. We don't
> > want to take a page fault while running some 80hz task, just because some
> > non-real time application tried to use what little physical memory we
> > allow for the kernel and all other applications.
> >
> > I asked a related question about a week ago on linux-mm and didn't get a
> > response. Basically, I was concerned that top did not show RSS == Size
> > when mlockall(MCL_CURRENT|MCL_FUTURE) was called. Could this explain the
> > difference or is there something else that I'm missing here?
>
> That mlockall should have faulted everything in.  It could be an
> accounting bug, or it could be a bug.  That's not an aspect which
> gets tested a lot.  I'll take a look.


This is what the manpage says...

       mlockall  disables  paging  for  all pages mapped into the
       address space of the calling process.  This  includes  the
       pages  of  the  code,  data  and stack segment, as well as
       shared libraries, user space kernel  data,  shared  memory
       and  memory  mapped files. All mapped pages are guaranteed
       to be resident  in  RAM  when  the  mlockall  system  call
       returns  successfully  and  they are guaranteed to stay in
       RAM until the pages  are  unlocked  again  by  munlock  or
       munlockall  or  until  the  process  terminates  or starts
       another program with exec.  Child processes do not inherit
       page locks across a fork.

Do you read that all pages must be faulted in apriori ?
Or is it sufficient to to make sure non of the currently mapped 
pages are swapped out and future swapout is prohibited.

This still allows for page faults on pages that have not been
mapped in the specified range or process. If required the 
app could touch these and they wouldn't be swapped later.


-- 
-- Hubertus Franke  (frankeh@watson.ibm.com)

Re: [PATCH] recognize MAP_LOCKED in mmap() call

[Andrew Morton]

Hubertus Franke wrote:
> 
> ...
> This is what the manpage says...
> 
>        mlockall  disables  paging  for  all pages mapped into the
>        address space of the calling process.  This  includes  the
>        pages  of  the  code,  data  and stack segment, as well as
>        shared libraries, user space kernel  data,  shared  memory
>        and  memory  mapped files. All mapped pages are guaranteed
>        to be resident  in  RAM  when  the  mlockall  system  call
>        returns  successfully  and  they are guaranteed to stay in
>        RAM until the pages  are  unlocked  again  by  munlock  or
>        munlockall  or  until  the  process  terminates  or starts
>        another program with exec.  Child processes do not inherit
>        page locks across a fork.
> 
> Do you read that all pages must be faulted in apriori ?

For MCL_FUTURE.

> Or is it sufficient to to make sure non of the currently mapped
> pages are swapped out and future swapout is prohibited.

I'd say that we should try to make all the pages present.  But
if it's a problem for (say) a hugepage implementation then it's
unlikely that the world would end if these things were still
demand paged in.

Re: [PATCH] recognize MAP_LOCKED in mmap() call

[Hubertus Franke]

On Wednesday 18 September 2002 03:18 pm, Mark_H_Johnson@raytheon.com wrote:
> Andrew Morton wrote:
> >(SuS really only anticipates that mmap needs to look at prior mlocks
> >in force against the address range.  It also says
> >
> >     Process memory locking does apply to shared memory regions,
> >
> >and we don't do that either.  I think we should; can't see why SuS
> >requires this.)
>
> Let me make sure I read what you said correctly. Does this mean that Linux
> 2.4 (or 2.5) kernels do not lock shared memory regions if a process uses
> mlockall?
>
> If not, that is *really bad* for our real time applications. We don't want
> to take a page fault while running some 80hz task, just because some
> non-real time application tried to use what little physical memory we allow
> for the kernel and all other applications.
>
> I asked a related question about a week ago on linux-mm and didn't get a
> response. Basically, I was concerned that top did not show RSS == Size when
> mlockall(MCL_CURRENT|MCL_FUTURE) was called. Could this explain the
> difference or is there something else that I'm missing here?
>
> Thanks.
> --Mark H Johnson
>   <mailto:Mark_H_Johnson@raytheon.com>


Sorry for the lengthy delay.
mlock() and mlockall() do the right thing..
however, mmap(MAP_LOCKED) should behave like a    mmap | mlock operation 
according to the manpages. This however was not implemented as the 
transformation from the mmap_flags to vm_flags never checked for MAP_LOCKED
but only for mm->def_flags which only covers a previous mlockall() call.

Hope this clarifies it .
-- 
-- Hubertus Franke  (frankeh@watson.ibm.com)

[PATCH] per-zone kswapd process

[Dave Hansen]

[-- Attachment #1: Type: text/plain, Size: 1119 bytes --]

This patch implements a kswapd process for each memory zone.  The original code 
came from Bill Irwin, but the current VM is quite a bit different from the one 
that he wrote it for, so not much remains.  The current kswapd interface is much 
more simple than before because there is a single waitqueue and there is a 
single place where it is emptied.

kswapd_can_sleep() and kswapd_balance() are simpler now that the extra pgdat 
level of indirection is gone.

Tested on 8-way PIII with highmem off and then 4GB support.  With 4GB support, I 
did 20 parallel greps through a 10GB fileset while some other processes 
allocated and freed 1-2GB chunks of memory.  That gave kswapd a good workout, 
and I observed it running the zone Highmem and zone Normal kswapd threads.  So, 
it survives my torture test.  It also removes more code than it adds.

include/linux/mmzone.h |    2 +
include/linux/swap.h   |    1
mm/page_alloc.c        |   11 +++++-
mm/vmscan.c            |   88 +++++++++++++++++--------------------------------
4 files changed, 42 insertions(+), 60 deletions(-)

-- 
Dave Hansen
haveblue@us.ibm.com




[-- Attachment #2: per-zone-kswapd-2.5.34-mm2-3.patch --]
[-- Type: text/plain, Size: 6092 bytes --]

# This is a BitKeeper generated patch for the following project:
# Project Name: Linux kernel tree
# This patch format is intended for GNU patch command version 2.5 or higher.
# This patch includes the following deltas:
#	           ChangeSet	1.625   -> 1.628  
#	include/linux/mmzone.h	1.19    -> 1.20   
#	include/linux/swap.h	1.57    -> 1.58   
#	     mm/page_alloc.c	1.98    -> 1.101  
#	         mm/vmscan.c	1.102   -> 1.105  
#
# The following is the BitKeeper ChangeSet Log
# --------------------------------------------
# 02/09/12	haveblue@elm3b96.(none)	1.626
# add per-zone kswapd
# --------------------------------------------
# 02/09/12	haveblue@elm3b96.(none)	1.627
# fix some wli-indicated formatting bits
# --------------------------------------------
# 02/09/12	haveblue@elm3b96.(none)	1.628
# move waitqueue init to a more appropriate place 
# --------------------------------------------
#
diff -Nru a/include/linux/mmzone.h b/include/linux/mmzone.h
--- a/include/linux/mmzone.h	Thu Sep 12 20:24:39 2002
+++ b/include/linux/mmzone.h	Thu Sep 12 20:24:39 2002
@@ -108,6 +108,8 @@
 	unsigned long		wait_table_size;
 	unsigned long		wait_table_bits;
 
+	wait_queue_head_t       kswapd_wait;	
+	
 	/*
 	 * Discontig memory support fields.
 	 */
diff -Nru a/include/linux/swap.h b/include/linux/swap.h
--- a/include/linux/swap.h	Thu Sep 12 20:24:39 2002
+++ b/include/linux/swap.h	Thu Sep 12 20:24:39 2002
@@ -162,7 +162,6 @@
 extern void swap_setup(void);
 
 /* linux/mm/vmscan.c */
-extern wait_queue_head_t kswapd_wait;
 extern int try_to_free_pages(struct zone *, unsigned int, unsigned int);
 
 /* linux/mm/page_io.c */
diff -Nru a/mm/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c	Thu Sep 12 20:24:39 2002
+++ b/mm/page_alloc.c	Thu Sep 12 20:24:39 2002
@@ -345,8 +345,15 @@
 	classzone->need_balance = 1;
 	mb();
 	/* we're somewhat low on memory, failed to find what we needed */
-	if (waitqueue_active(&kswapd_wait))
-		wake_up_interruptible(&kswapd_wait);
+	for (i = 0; zones[i] != NULL; i++) {
+		struct zone *z = zones[i];
+
+		/* We don't want to go swapping on zones that aren't actually
+		 * low.  This accounts for "incremental min" from last loop */
+		if (z->free_pages <= z->pages_low &&
+		    waitqueue_active(&z->kswapd_wait)) 
+			wake_up_interruptible(&z->kswapd_wait);
+	}
 
 	/* Go through the zonelist again, taking __GFP_HIGH into account */
 	min = 1UL << order;
@@ -874,6 +881,8 @@
 		for(i = 0; i < zone->wait_table_size; ++i)
 			init_waitqueue_head(zone->wait_table + i);
 
+		init_waitqueue_head(&zone->kswapd_wait);
+		
 		pgdat->nr_zones = j+1;
 
 		mask = (realsize / zone_balance_ratio[j]);
diff -Nru a/mm/vmscan.c b/mm/vmscan.c
--- a/mm/vmscan.c	Thu Sep 12 20:24:39 2002
+++ b/mm/vmscan.c	Thu Sep 12 20:24:39 2002
@@ -713,8 +713,6 @@
 	return 0;
 }
 
-DECLARE_WAIT_QUEUE_HEAD(kswapd_wait);
-
 static int check_classzone_need_balance(struct zone *classzone)
 {
 	struct zone *first_classzone;
@@ -728,71 +726,33 @@
 	return 1;
 }
 
-static int kswapd_balance_pgdat(pg_data_t * pgdat)
+static int kswapd_balance_zone(struct zone *zone)
 {
-	int need_more_balance = 0, i;
-	struct zone *zone;
-
-	for (i = pgdat->nr_zones-1; i >= 0; i--) {
-		zone = pgdat->node_zones + i;
+	int need_more_balance = 0;
+	
+	do {
 		cond_resched();
 		if (!zone->need_balance)
-			continue;
+			break;
 		if (!try_to_free_pages(zone, GFP_KSWAPD, 0)) {
 			zone->need_balance = 0;
 			__set_current_state(TASK_INTERRUPTIBLE);
 			schedule_timeout(HZ);
-			continue;
+			break;
 		}
 		if (check_classzone_need_balance(zone))
 			need_more_balance = 1;
 		else
 			zone->need_balance = 0;
-	}
-
-	return need_more_balance;
-}
-
-static void kswapd_balance(void)
-{
-	int need_more_balance;
-	pg_data_t * pgdat;
-
-	do {
-		need_more_balance = 0;
-		pgdat = pgdat_list;
-		do
-			need_more_balance |= kswapd_balance_pgdat(pgdat);
-		while ((pgdat = pgdat->pgdat_next));
 	} while (need_more_balance);
-}
 
-static int kswapd_can_sleep_pgdat(pg_data_t * pgdat)
-{
-	struct zone *zone;
-	int i;
-
-	for (i = pgdat->nr_zones-1; i >= 0; i--) {
-		zone = pgdat->node_zones + i;
-		if (!zone->need_balance)
-			continue;
-		return 0;
-	}
-
-	return 1;
+	return 0;
 }
 
-static int kswapd_can_sleep(void)
+static int kswapd_can_sleep_zone(struct zone *zone)
 {
-	pg_data_t * pgdat;
-
-	pgdat = pgdat_list;
-	do {
-		if (kswapd_can_sleep_pgdat(pgdat))
-			continue;
-		return 0;
-	} while ((pgdat = pgdat->pgdat_next));
-
+	if (zone->need_balance)
+		return 0;	
 	return 1;
 }
 
@@ -809,13 +769,18 @@
  * If there are applications that are active memory-allocators
  * (most normal use), this basically shouldn't matter.
  */
-int kswapd(void *unused)
+int kswapd_zone(void *p)
 {
+	struct zone *zone = (struct zone *)p;
 	struct task_struct *tsk = current;
 	DECLARE_WAITQUEUE(wait, tsk);
+	
+	printk( "kswapd%d starting for %s\n", 
+			zone - zone->zone_pgdat->node_zones, 
+			zone->name);
 
 	daemonize();
-	strcpy(tsk->comm, "kswapd");
+	sprintf(tsk->comm, "kswapd%d", zone - zone->zone_pgdat->node_zones);
 	sigfillset(&tsk->blocked);
 	
 	/*
@@ -839,30 +804,37 @@
 		if (current->flags & PF_FREEZE)
 			refrigerator(PF_IOTHREAD);
 		__set_current_state(TASK_INTERRUPTIBLE);
-		add_wait_queue(&kswapd_wait, &wait);
+		add_wait_queue(&zone->kswapd_wait, &wait);
 
 		mb();
-		if (kswapd_can_sleep())
+		if (kswapd_can_sleep_zone(zone))
 			schedule();
 
 		__set_current_state(TASK_RUNNING);
-		remove_wait_queue(&kswapd_wait, &wait);
+		remove_wait_queue(&zone->kswapd_wait, &wait);
 
 		/*
 		 * If we actually get into a low-memory situation,
 		 * the processes needing more memory will wake us
 		 * up on a more timely basis.
 		 */
-		kswapd_balance();
+		kswapd_balance_zone(zone);
 		blk_run_queues();
 	}
 }
 
 static int __init kswapd_init(void)
 {
+	struct zone* zone;
+
 	printk("Starting kswapd\n");
 	swap_setup();
-	kernel_thread(kswapd, NULL, CLONE_FS | CLONE_FILES | CLONE_SIGNAL);
+	for_each_zone(zone)
+		if (zone->size)
+			kernel_thread(kswapd_zone, 
+				      zone, 
+				      CLONE_FS | CLONE_FILES | CLONE_SIGNAL);
+	
 	return 0;
 }
 

Re: [PATCH] per-zone kswapd process

[Alan Cox]

On Fri, 2002-09-13 at 05:59, William Lee Irwin III wrote:
> Machines without observable NUMA effects can benefit from it if it's
> per-zone. It also follows that if there's more than one task doing this,
> page replacement is less likely to block entirely. Last, but not least,
> when I devised it, "per-zone" was the theme.

It will also increase the amount of disk head thrashing surely ?

Re: [PATCH] per-zone kswapd process

[William Lee Irwin III]

On Fri, 2002-09-13 at 05:59, William Lee Irwin III wrote:
>> Machines without observable NUMA effects can benefit from it if it's
>> per-zone. It also follows that if there's more than one task doing this,
>> page replacement is less likely to block entirely. Last, but not least,
>> when I devised it, "per-zone" was the theme.

On Fri, Sep 13, 2002 at 02:05:52PM +0100, Alan Cox wrote:
> It will also increase the amount of disk head thrashing surely ?

I doubt it. Writeout isn't really supposed to happen there in 2.4
either, except under duress. OTOH I've not been doing much with this
directly since rmap10c.


Cheers,
Bill

[PATCH] recognize MAP_LOCKED in mmap() call

[Hubertus Franke]

[-- Attachment #1: Type: text/plain, Size: 1017 bytes --]


Andrew, at the current time an mmap() ignores a MAP_LOCKED passed to it.
The only way we can get VM_LOCKED associated with the newly created VMA
is to have previously called mlockall() on the process which sets the 
mm->def_flags != VM_LOCKED or subsequently call mlock() on the
newly created VMA.

The attached patch checks for MAP_LOCKED being passed and if so checks
the capabilities of the process. Limit checks were already in place.
-- 
-- Hubertus Franke  (frankeh@watson.ibm.com)

--------------------------------< PATCH >------------------------------
--- linux-2.5.35/mm/mmap.c	Wed Sep 18 11:12:13 2002
+++ linux-2.5.35-fix/mm/mmap.c	Wed Sep 18 11:44:32 2002
@@ -461,6 +461,11 @@
 	 */
 	vm_flags = calc_vm_flags(prot,flags) | mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
 
+	if (flags & MAP_LOCKED) {
+		if (!capable(CAP_IPC_LOCK))
+			return -EPERM;
+		vm_flags |= VM_LOCKED;
+	}
 	/* mlock MCL_FUTURE? */
 	if (vm_flags & VM_LOCKED) {
 		unsigned long locked = mm->locked_vm << PAGE_SHIFT;




[-- Attachment #2: patch.2.5.35.mmap_locked --]
[-- Type: text/x-diff, Size: 452 bytes --]

--- linux-2.5.35/mm/mmap.c	Wed Sep 18 11:12:13 2002
+++ linux-2.5.35-fix/mm/mmap.c	Wed Sep 18 11:44:32 2002
@@ -461,6 +461,11 @@
 	 */
 	vm_flags = calc_vm_flags(prot,flags) | mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
 
+	if (flags & MAP_LOCKED) {
+		if (!capable(CAP_IPC_LOCK))
+			return -EPERM;
+		vm_flags |= VM_LOCKED;
+	}
 	/* mlock MCL_FUTURE? */
 	if (vm_flags & VM_LOCKED) {
 		unsigned long locked = mm->locked_vm << PAGE_SHIFT;

Re: [PATCH] recognize MAP_LOCKED in mmap() call

[Andrew Morton]

Hubertus Franke wrote:
> 
> Andrew, at the current time an mmap() ignores a MAP_LOCKED passed to it.
> The only way we can get VM_LOCKED associated with the newly created VMA
> is to have previously called mlockall() on the process which sets the
> mm->def_flags != VM_LOCKED or subsequently call mlock() on the
> newly created VMA.
> 
> The attached patch checks for MAP_LOCKED being passed and if so checks
> the capabilities of the process. Limit checks were already in place.

Looks sane, thanks.

It appears that MAP_LOCKED is a Linux-special, so presumably it
_used_ to work.  I wonder when it broke?

You patch applies to 2.4 as well; it would be useful to give that
a sanity test and send a copy to Marcelo.

(SuS really only anticipates that mmap needs to look at prior mlocks
in force against the address range.  It also says

     Process memory locking does apply to shared memory regions,

and we don't do that either.  I think we should; can't see why SuS
requires this.)