[PATCH 01/05] mm fix __alloc_pages cpuset ALLOC_* flags

[PATCH 01/05] mm fix __alloc_pages cpuset ALLOC_* flags

[Paul Jackson]

Two changes to the setting of the ALLOC_CPUSET flag in
mm/page_alloc.c:__alloc_pages()

 1) A bug fix - the "ignoring mins" case should not be honoring
    ALLOC_CPUSET.  This case of all cases, since it is handling a
    request that will free up more memory than is asked for (exiting
    tasks, e.g.) should be allowed to escape cpuset constraints
    when memory is tight.

 2) A logic change to make it simpler.  Honor cpusets even on
    GFP_ATOMIC (!wait) requests.  With this, cpuset confinement
    applies to all requests except ALLOC_NO_WATERMARKS, so that
    in a subsequent cleanup patch, I can remove the ALLOC_CPUSET
    flag entirely.  Since I don't know any real reason this
    logic has to be either way, I am choosing the path of the
    simplest code.

Signed-off-by: Paul Jackson <pj@sgi.com>

---

 mm/page_alloc.c |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

--- 2.6.14-mm2.orig/mm/page_alloc.c	2005-11-12 22:25:03.305301135 -0800
+++ 2.6.14-mm2/mm/page_alloc.c	2005-11-12 22:27:30.519813285 -0800
@@ -933,8 +933,7 @@ restart:
 		alloc_flags |= ALLOC_HARDER;
 	if (gfp_mask & __GFP_HIGH)
 		alloc_flags |= ALLOC_HIGH;
-	if (wait)
-		alloc_flags |= ALLOC_CPUSET;
+	alloc_flags |= ALLOC_CPUSET;
 
 	/*
 	 * Go through the zonelist again. Let __GFP_HIGH and allocations
@@ -956,7 +955,7 @@ restart:
 nofail_alloc:
 			/* go through the zonelist yet again, ignoring mins */
 			page = get_page_from_freelist(gfp_mask, order,
-				zonelist, ALLOC_NO_WATERMARKS|ALLOC_CPUSET);
+				zonelist, ALLOC_NO_WATERMARKS);
 			if (page)
 				goto got_pg;
 			if (gfp_mask & __GFP_NOFAIL) {

-- 
                          I won't rest till it's the best ...
                          Programmer, Linux Scalability
                          Paul Jackson <pj@sgi.com> 1.650.933.1373

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[PATCH 02/05] mm simplify __alloc_pages cpuset ALLOC_* flags

[Paul Jackson]

Remove ALLOC_CPUSET flag from mm/page_alloc.c:__alloc_pages().
Thanks to the previous patch, it is equivalent to the setting
of !ALLOC_NO_WATERMARKS, so redundant.

Signed-off-by: Paul Jackson <pj@sgi.com>

---

 mm/page_alloc.c |   12 ++++--------
 1 files changed, 4 insertions(+), 8 deletions(-)

--- 2.6.14-mm2.orig/mm/page_alloc.c	2005-11-12 22:27:30.519813285 -0800
+++ 2.6.14-mm2/mm/page_alloc.c	2005-11-12 22:28:35.792016688 -0800
@@ -758,7 +758,6 @@ buffered_rmqueue(struct zone *zone, int 
 #define ALLOC_NO_WATERMARKS	0x01 /* don't check watermarks at all */
 #define ALLOC_HARDER		0x02 /* try to alloc harder */
 #define ALLOC_HIGH		0x04 /* __GFP_HIGH set */
-#define ALLOC_CPUSET		0x08 /* check for correct cpuset */
 
 /*
  * Return 1 if free pages are above 'mark'. This takes into account the order
@@ -814,11 +813,9 @@ get_page_from_freelist(gfp_t gfp_mask, u
 	 * See also cpuset_zone_allowed() comment in kernel/cpuset.c.
 	 */
 	do {
-		if ((alloc_flags & ALLOC_CPUSET) &&
-				!cpuset_zone_allowed(*z, gfp_mask))
-			continue;
-
 		if (!(alloc_flags & ALLOC_NO_WATERMARKS)) {
+			if (!cpuset_zone_allowed(*z, gfp_mask))
+				continue;
 			if (!zone_watermark_ok(*z, order, (*z)->pages_low,
 				    classzone_idx, alloc_flags))
 				continue;
@@ -911,7 +908,7 @@ __alloc_pages(gfp_t gfp_mask, unsigned i
 	}
 restart:
 	page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, order,
-				zonelist, ALLOC_CPUSET);
+				zonelist, 0);
 	if (page)
 		goto got_pg;
 
@@ -933,7 +930,6 @@ restart:
 		alloc_flags |= ALLOC_HARDER;
 	if (gfp_mask & __GFP_HIGH)
 		alloc_flags |= ALLOC_HIGH;
-	alloc_flags |= ALLOC_CPUSET;
 
 	/*
 	 * Go through the zonelist again. Let __GFP_HIGH and allocations
@@ -999,7 +995,7 @@ rebalance:
 		 * under heavy pressure.
 		 */
 		page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, order,
-						zonelist, ALLOC_CPUSET);
+						zonelist, 0);
 		if (page)
 			goto got_pg;
 

-- 
                          I won't rest till it's the best ...
                          Programmer, Linux Scalability
                          Paul Jackson <pj@sgi.com> 1.650.933.1373

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[PATCH 03/05] mm rationalize __alloc_pages ALLOC_* flag names

[Paul Jackson]

Rationalize mm/page_alloc.c:__alloc_pages() ALLOC flag names.

The case where we should be nice and not dip into memory reserves
had been hiding behind the ALLOC_CPUSET flag, but with that gone,
had no name and was a naked "0" value.

It was not clear which of HARDER or HIGH was harder, and it
was not clear how ALLOC_HIGH related to the allocation policy
for dipping into reserves.

Finally, the names and numeric order did not reflect the natural
order of increasing urgency (increasing willingness to dip
into reserves.)

Rename and renumber these flags to fix above.

A comment "Go through the zonelist again ..." explaining some
of this was obsolete, and adequately covered by a modestly
modified earlier comment, so bye bye obsolete comment.

Signed-off-by: Paul Jackson <pj@sgi.com>

---

 mm/page_alloc.c |   33 +++++++++++++--------------------
 1 files changed, 13 insertions(+), 20 deletions(-)

--- 2.6.14-mm2.orig/mm/page_alloc.c	2005-11-13 10:04:26.214796388 -0800
+++ 2.6.14-mm2/mm/page_alloc.c	2005-11-13 10:10:59.147820307 -0800
@@ -755,9 +755,10 @@ buffered_rmqueue(struct zone *zone, int 
 	return page;
 }
 
-#define ALLOC_NO_WATERMARKS	0x01 /* don't check watermarks at all */
-#define ALLOC_HARDER		0x02 /* try to alloc harder */
-#define ALLOC_HIGH		0x04 /* __GFP_HIGH set */
+#define ALLOC_DONT_DIP	0x01 	/* don't dip into memory reserves */
+#define ALLOC_DIP_SOME	0x02 	/* dip into reserves some */
+#define ALLOC_DIP_ALOT	0x04 	/* dip into reserves further */
+#define ALLOC_MUSTHAVE	0x08 	/* ignore all constraints */
 
 /*
  * Return 1 if free pages are above 'mark'. This takes into account the order
@@ -770,9 +771,9 @@ int zone_watermark_ok(struct zone *z, in
 	long min = mark, free_pages = z->free_pages - (1 << order) + 1;
 	int o;
 
-	if (alloc_flags & ALLOC_HIGH)
+	if (alloc_flags & ALLOC_DIP_SOME)
 		min -= min / 2;
-	if (alloc_flags & ALLOC_HARDER)
+	if (alloc_flags & ALLOC_DIP_ALOT)
 		min -= min / 4;
 
 	if (free_pages <= min + z->lowmem_reserve[classzone_idx])
@@ -813,7 +814,7 @@ get_page_from_freelist(gfp_t gfp_mask, u
 	 * See also cpuset_zone_allowed() comment in kernel/cpuset.c.
 	 */
 	do {
-		if (!(alloc_flags & ALLOC_NO_WATERMARKS)) {
+		if (!(alloc_flags & ALLOC_MUSTHAVE)) {
 			if (!cpuset_zone_allowed(*z, gfp_mask))
 				continue;
 			if (!zone_watermark_ok(*z, order, (*z)->pages_low,
@@ -908,7 +909,7 @@ __alloc_pages(gfp_t gfp_mask, unsigned i
 	}
 restart:
 	page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, order,
-				zonelist, 0);
+				zonelist, ALLOC_DONT_DIP);
 	if (page)
 		goto got_pg;
 
@@ -923,22 +924,14 @@ restart:
 	 *
 	 * The caller may dip into page reserves a bit more if the caller
 	 * cannot run direct reclaim, or if the caller has realtime scheduling
-	 * policy.
+	 * policy or is asking for __GFP_HIGH memory.
 	 */
 	alloc_flags = 0;
 	if ((unlikely(rt_task(p)) && !in_interrupt()) || !wait)
-		alloc_flags |= ALLOC_HARDER;
+		alloc_flags |= ALLOC_DIP_ALOT;
 	if (gfp_mask & __GFP_HIGH)
-		alloc_flags |= ALLOC_HIGH;
+		alloc_flags |= ALLOC_DIP_SOME;
 
-	/*
-	 * Go through the zonelist again. Let __GFP_HIGH and allocations
-	 * coming from realtime tasks go deeper into reserves.
-	 *
-	 * This is the last chance, in general, before the goto nopage.
-	 * Ignore cpuset if GFP_ATOMIC (!wait) rather than fail alloc.
-	 * See also cpuset_zone_allowed() comment in kernel/cpuset.c.
-	 */
 	page = get_page_from_freelist(gfp_mask, order, zonelist, alloc_flags);
 	if (page)
 		goto got_pg;
@@ -951,7 +944,7 @@ restart:
 nofail_alloc:
 			/* go through the zonelist yet again, ignoring mins */
 			page = get_page_from_freelist(gfp_mask, order,
-				zonelist, ALLOC_NO_WATERMARKS);
+				zonelist, ALLOC_MUSTHAVE);
 			if (page)
 				goto got_pg;
 			if (gfp_mask & __GFP_NOFAIL) {
@@ -995,7 +988,7 @@ rebalance:
 		 * under heavy pressure.
 		 */
 		page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, order,
-						zonelist, 0);
+						zonelist, ALLOC_DONT_DIP);
 		if (page)
 			goto got_pg;
 

-- 
                          I won't rest till it's the best ...
                          Programmer, Linux Scalability
                          Paul Jackson <pj@sgi.com> 1.650.933.1373

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Re: [PATCH 03/05] mm rationalize __alloc_pages ALLOC_* flag names

[Nick Piggin]

Paul Jackson wrote:
> Rationalize mm/page_alloc.c:__alloc_pages() ALLOC flag names.
> 

I don't really see the need for this. The names aren't
clearly better, and the downside is that they move away
from the terminlogy we've been using in the page allocator
for the past few years.

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Re: [PATCH 03/05] mm rationalize __alloc_pages ALLOC_* flag names

[Andrew Morton]

Nick Piggin <nickpiggin@yahoo.com.au> wrote:
>
> Paul Jackson wrote:
> > Rationalize mm/page_alloc.c:__alloc_pages() ALLOC flag names.
> > 
> 
> I don't really see the need for this. The names aren't
> clearly better, and the downside is that they move away
> from the terminlogy we've been using in the page allocator
> for the past few years.

I thought they were heaps better, actually.

-#define ALLOC_NO_WATERMARKS	0x01 /* don't check watermarks at all */
-#define ALLOC_HARDER		0x02 /* try to alloc harder */
-#define ALLOC_HIGH		0x04 /* __GFP_HIGH set */
+#define ALLOC_DONT_DIP	0x01 	/* don't dip into memory reserves */
+#define ALLOC_DIP_SOME	0x02 	/* dip into reserves some */
+#define ALLOC_DIP_ALOT	0x04 	/* dip into reserves further */
+#define ALLOC_MUSTHAVE	0x08 	/* ignore all constraints */

very explicit.

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Re: [PATCH 03/05] mm rationalize __alloc_pages ALLOC_* flag names

[Nick Piggin]

Andrew Morton wrote:
> Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> 
>>Paul Jackson wrote:
>>
>>>Rationalize mm/page_alloc.c:__alloc_pages() ALLOC flag names.
>>>
>>
>>I don't really see the need for this. The names aren't
>>clearly better, and the downside is that they move away
>>from the terminlogy we've been using in the page allocator
>>for the past few years.
> 
> 
> I thought they were heaps better, actually.
> 

Some? Alot? Musthave?

To me it just changed the manner in which the hands are waving.
Actually, I like the current names because ALLOC_HIGH explicitly
is used for __GFP_HIGH allocations, and MUSTHAVE is not really
an improvement on NO_WATERMARKS.

However if you'd really like to change the names, I'd prefer them
to be more consistent, eg:

ALLOC_DIP_NONE
ALLOC_DIP_LESS
ALLOC_DIP_MORE
ALLOC_DIP_FULL

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Re: [PATCH 03/05] mm rationalize __alloc_pages ALLOC_* flag names

[Paul Jackson]

Nick suggested:
> ALLOC_DIP_NONE
> ALLOC_DIP_LESS
> ALLOC_DIP_MORE
> ALLOC_DIP_FULL

Sweet.  PATCH coming soon.

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                  Paul Jackson <pj@sgi.com> 1.925.600.0401

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Re: [PATCH 03/05] mm rationalize __alloc_pages ALLOC_* flag names

[Arjan van de Ven]

On Tue, 2005-11-15 at 01:03 -0800, Andrew Morton wrote:
> Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> >
> > Paul Jackson wrote:
> > > Rationalize mm/page_alloc.c:__alloc_pages() ALLOC flag names.
> > > 
> > 
> > I don't really see the need for this. The names aren't
> > clearly better, and the downside is that they move away
> > from the terminlogy we've been using in the page allocator
> > for the past few years.
> 
> I thought they were heaps better, actually.
> 
> -#define ALLOC_NO_WATERMARKS	0x01 /* don't check watermarks at all */
> -#define ALLOC_HARDER		0x02 /* try to alloc harder */
> -#define ALLOC_HIGH		0x04 /* __GFP_HIGH set */
> +#define ALLOC_DONT_DIP	0x01 	/* don't dip into memory reserves */
> +#define ALLOC_DIP_SOME	0x02 	/* dip into reserves some */
> +#define ALLOC_DIP_ALOT	0x04 	/* dip into reserves further */
> +#define ALLOC_MUSTHAVE	0x08 	/* ignore all constraints */
> 
> very explicit.

maybe. 
however... if names get changed anyway, maybe name them based on intent?

ALLOC_NORMAL  
ALLOC_KERNELTHREAD
ALLOC_VMCAUSED
ALLOC_WOULDDEADLOCK 

or something.. yes these are lame

perhaps both are needed.. bitflags for the implementation, and defines
based on usage that are compounded bitflags..


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Re: [PATCH 03/05] mm rationalize __alloc_pages ALLOC_* flag names

[Paul Jackson]

Nick wrote:
> the downside is that they move away
> from the terminlogy we've been using in the page allocator
> for the past few years.

I was trying to make the names more readable for the rest of us ;).

In the short term, there is seldom a reason to change names,
as it impacts the current experts more than it helps others.

Over a sufficiently long term, everyone is an 'other'.  Most
of the people who will have reason to want to understand this
code over the next five years are not experts in it now.

-- 
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                  Programmer, Linux Scalability
                  Paul Jackson <pj@sgi.com> 1.925.600.0401

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[PATCH 04/05] mm simplify __alloc_pages cpuset hardwall logic

[Paul Jackson]

The __GFP_HARDWALL flag logic is the same in mm/page_alloc.c
for all calls to get_page_from_freelist().  Save a couple of
lines of source code and a few bytes of text by only computing
it once, inside get_page_from_freelist(), instead of passing
it in each time.  The key improvement is that it reduces the
logic in __alloc_pages() by another detail.  There is now -no-
cpuset specific confinement logic in __alloc_pages().  It is
all more generically stated in get_page_from_freelist().

Signed-off-by: Paul Jackson <pj@sgi.com>

---

 mm/page_alloc.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

--- 2.6.14-mm2.orig/mm/page_alloc.c	2005-11-13 10:10:59.147820307 -0800
+++ 2.6.14-mm2/mm/page_alloc.c	2005-11-13 10:11:02.926182092 -0800
@@ -815,6 +815,8 @@ get_page_from_freelist(gfp_t gfp_mask, u
 	 */
 	do {
 		if (!(alloc_flags & ALLOC_MUSTHAVE)) {
+			if (alloc_flags == ALLOC_DONT_DIP)
+				gfp_mask |= __GFP_HARDWALL;
 			if (!cpuset_zone_allowed(*z, gfp_mask))
 				continue;
 			if (!zone_watermark_ok(*z, order, (*z)->pages_low,
@@ -908,7 +910,7 @@ __alloc_pages(gfp_t gfp_mask, unsigned i
 		return NULL;
 	}
 restart:
-	page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, order,
+	page = get_page_from_freelist(gfp_mask, order,
 				zonelist, ALLOC_DONT_DIP);
 	if (page)
 		goto got_pg;
@@ -987,7 +989,7 @@ rebalance:
 		 * a parallel oom killing, we must fail if we're still
 		 * under heavy pressure.
 		 */
-		page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, order,
+		page = get_page_from_freelist(gfp_mask, order,
 						zonelist, ALLOC_DONT_DIP);
 		if (page)
 			goto got_pg;

-- 
                          I won't rest till it's the best ...
                          Programmer, Linux Scalability
                          Paul Jackson <pj@sgi.com> 1.650.933.1373

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[PATCH 05/05] mm GFP_ATOMIC comment

[Paul Jackson]

Clarify in comments that GFP_ATOMIC means both "don't sleep"
and "use emergency pools", hence both ALLOC_DIP_ALOT and
ALLOC_DIP_SOME.

Signed-off-by: Paul Jackson <pj@sgi.com>

---

 include/linux/gfp.h |    1 +
 mm/page_alloc.c     |    3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)

--- 2.6.14-mm2.orig/include/linux/gfp.h	2005-11-13 09:57:03.317369370 -0800
+++ 2.6.14-mm2/include/linux/gfp.h	2005-11-13 10:31:05.590802684 -0800
@@ -58,6 +58,7 @@ struct vm_area_struct;
 			__GFP_NOFAIL|__GFP_NORETRY|__GFP_NO_GROW|__GFP_COMP| \
 			__GFP_NOMEMALLOC|__GFP_HARDWALL)
 
+/* GFP_ATOMIC means both !wait (__GFP_WAIT not set) and use emergency pool */
 #define GFP_ATOMIC	(__GFP_VALID | __GFP_HIGH)
 #define GFP_NOIO	(__GFP_VALID | __GFP_WAIT)
 #define GFP_NOFS	(__GFP_VALID | __GFP_WAIT | __GFP_IO)
--- 2.6.14-mm2.orig/mm/page_alloc.c	2005-11-13 10:21:13.804965981 -0800
+++ 2.6.14-mm2/mm/page_alloc.c	2005-11-13 10:32:33.090792563 -0800
@@ -926,7 +926,8 @@ restart:
 	 *
 	 * The caller may dip into page reserves a bit more if the caller
 	 * cannot run direct reclaim, or if the caller has realtime scheduling
-	 * policy or is asking for __GFP_HIGH memory.
+	 * policy or is asking for __GFP_HIGH memory.  GFP_ATOMIC requests will
+	 * set both ALLOC_DIP_ALOT (!wait) and ALLOC_DIP_SOME (__GFP_HIGH).
 	 */
 	alloc_flags = 0;
 	if ((unlikely(rt_task(p)) && !in_interrupt()) || !wait)

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                          Programmer, Linux Scalability
                          Paul Jackson <pj@sgi.com> 1.650.933.1373

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Re: [PATCH 01/05] mm fix __alloc_pages cpuset ALLOC_* flags

[Nick Piggin]

Paul Jackson wrote:
> Two changes to the setting of the ALLOC_CPUSET flag in
> mm/page_alloc.c:__alloc_pages()
> 
>  1) A bug fix - the "ignoring mins" case should not be honoring
>     ALLOC_CPUSET.  This case of all cases, since it is handling a
>     request that will free up more memory than is asked for (exiting
>     tasks, e.g.) should be allowed to escape cpuset constraints
>     when memory is tight.
> 
>  2) A logic change to make it simpler.  Honor cpusets even on
>     GFP_ATOMIC (!wait) requests.  With this, cpuset confinement
>     applies to all requests except ALLOC_NO_WATERMARKS, so that
>     in a subsequent cleanup patch, I can remove the ALLOC_CPUSET
>     flag entirely.  Since I don't know any real reason this
>     logic has to be either way, I am choosing the path of the
>     simplest code.
> 

Hi,

I think #1 is OK, however I was under the impression that you
introduced the exception reverted in #2 due to seeing atomic
allocation failures?!

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Re: [PATCH 01/05] mm fix __alloc_pages cpuset ALLOC_* flags

[Paul Jackson]

Nick wrote:
> I was under the impression that you
> introduced the exception reverted in #2 due to seeing atomic
> allocation failures?!

For the record, the discussion Nick is recalling starts here:

  http://www.ussg.iu.edu/hypermail/linux/kernel/0503.3/0763.html

My motivation for letting GFP_ATOMIC requests escape cpuset confinement
was not based on seeing real world events, but based on code reading.

If some GFP_ATOMIC requests fail, the system can panic.  Apparently
these allocations are in init and setup code, where only a really
sick system could fail a kmalloc() anyway.  But, back then in March
2005, I concluded that GFP_ATOMIC requests were the absolute most
essential allocations to satisfy, at all costs, cpusets be damned.

This time around, when reading __alloc_pages() again, I realized that
GFP_ATOMIC requests did not get the highest priority in setting
watermarks.  Even they had to leave some reserves behind.  The only
allocations allowed to ignore all mins were the special case of
allocations that promised to free more memory than they were consuming,
really soon now (such as an exiting task).

I figured this time that what's good for watermark setting is good for
cpuset setting.

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@sgi.com> 1.925.600.0401

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