[PATCH]: Remove PF_MEMDIE as it is redundant

[PATCH]: Remove PF_MEMDIE as it is redundant

[Juan Quintela]

Hi
        PF_MEMDIE don't have any use in current kernels.  Please
        remove, we only set it in one place, and there we also set
        PF_MEMALLOC.  And we only test it in other place, and we also
        test for PF_MEMALLOC.  This patch has existed in aa for some
        quite time.

        Please apply.

        Later, Juan.

diff -urNp ref/include/linux/sched.h 2.4.20pre5aa1/include/linux/sched.h
--- ref/include/linux/sched.h	Fri Aug 30 01:55:20 2002
+++ 2.4.20pre5aa1/include/linux/sched.h	Fri Aug 30 01:55:22 2002
@@ -481,7 +481,6 @@ struct task_struct {
 #define PF_DUMPCORE	0x00000200	/* dumped core */
 #define PF_SIGNALED	0x00000400	/* killed by a signal */
 #define PF_MEMALLOC	0x00000800	/* Allocating memory */
-#define PF_MEMDIE	0x00001000	/* Killed for out-of-memory */
 #define PF_FREE_PAGES	0x00002000	/* per process page freeing */
 #define PF_NOIO		0x00004000	/* avoid generating further I/O */
 
diff -urNp ref/mm/oom_kill.c 2.4.20pre5aa1/mm/oom_kill.c
--- t3/mm/oom_kill.c.cc13-2.orig	2002-10-25 12:53:02.000000000 +0200
+++ t3/mm/oom_kill.c	2002-10-25 13:09:27.000000000 +0200
@@ -149,7 +149,7 @@ void oom_kill_task(struct task_struct *p
 	 * exit() and clear out its resources quickly...
 	 */
 	p->counter = 5 * HZ;
-	p->flags |= PF_MEMALLOC | PF_MEMDIE;
+	p->flags |= PF_MEMALLOC;
 
 	/* This process has hardware access, be more careful. */
 	if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO)) {
diff -uNp t1/mm/page_alloc.c.cc13-3.orig t1/mm/page_alloc.c
--- t1/mm/page_alloc.c.cc13-3.orig	2003-01-08 23:32:31.000000000 +0100
+++ t1/mm/page_alloc.c	2003-01-08 23:40:26.000000000 +0100
@@ -351,7 +351,7 @@ struct page * __alloc_pages(unsigned int
 	/* here we're in the low on memory slow path */
 
 rebalance:
-	if (current->flags & (PF_MEMALLOC | PF_MEMDIE)) {
+	if (current->flags & PF_MEMALLOC) {
 		zone = zonelist->zones;
 		for (;;) {
 			zone_t *z = *(zone++);





-- 
In theory, practice and theory are the same, but in practice they 
are different -- Larry McVoy

Re: [PATCH]: Remove PF_MEMDIE as it is redundant

[Robert Love]

On Wed, 2003-01-08 at 17:47, Juan Quintela wrote:

>         PF_MEMDIE don't have any use in current kernels.  Please
>         remove, we only set it in one place, and there we also set
>         PF_MEMALLOC.  And we only test it in other place, and we also
>         test for PF_MEMALLOC.  This patch has existed in aa for some
>         quite time.

I independently thought this same thing, and did a patch for 2.5 which
had the same effect.

I was reminded by better-VM-hackers-than-I that PF_MEMALLOC can be
cleared in various paths so the PF_MEMDIE is required to ensure that the
check in page_alloc.c is always true for OOM'ed tasks.

	Robert Love

Re: [PATCH]: Remove PF_MEMDIE as it is redundant

[Juan Quintela]

>>>>> "robert" == Robert Love <rml@tech9.net> writes:

robert> On Wed, 2003-01-08 at 17:47, Juan Quintela wrote:
>> PF_MEMDIE don't have any use in current kernels.  Please
>> remove, we only set it in one place, and there we also set
>> PF_MEMALLOC.  And we only test it in other place, and we also
>> test for PF_MEMALLOC.  This patch has existed in aa for some
>> quite time.

robert> I independently thought this same thing, and did a patch for 2.5 which
robert> had the same effect.

robert> I was reminded by better-VM-hackers-than-I that PF_MEMALLOC can be
robert> cleared in various paths so the PF_MEMDIE is required to ensure that the
robert> check in page_alloc.c is always true for OOM'ed tasks.

That is a nice theory, and I think that this could be true in the
past, but in 2.4.2X, PF_MEMDIE only appears in the two places that I
show, and it is completely redundant, look at the patch, we are just 
|-ing both PF_MEMALLOC and PF_MEMDIE and later we are &-ing against
the or of the two.  Use find & grep yourself if you don't believe me.

Later, Juan.

-- 
In theory, practice and theory are the same, but in practice they 
are different -- Larry McVoy

Re: [PATCH]: Remove PF_MEMDIE as it is redundant

[Robert Love]

On Wed, 2003-01-08 at 18:49, Juan Quintela wrote:

> That is a nice theory, and I think that this could be true in the
> past, but in 2.4.2X, PF_MEMDIE only appears in the two places that I
> show, and it is completely redundant, look at the patch, we are just 
> |-ing both PF_MEMALLOC and PF_MEMDIE and later we are &-ing against
> the or of the two.  Use find & grep yourself if you don't believe me.

I realize this.

The issue is that PF_MEMALLOC can be _cleared_.  In that case, if you
only set PF_MEMALLOC, that check can be false when we want it true.  So
we need a flag that is more persistent.

PF_MEMDIE, which is not cleared on various allocation paths in the VM,
ensures that the check holds true for all OOM'ed tasks.

I thought the same as you, "hey this thing is worthless let us dump it",
and Rik and Andrew told me otherwise.

I am not saying you are wrong, though - I could be very wrong.  But my
point is not what you say above; it is that the flag is needed because
just setting PF_MEMALLOC is insufficient since it can be unset.

	Robert Love

Re: [PATCH]: Remove PF_MEMDIE as it is redundant

[Juan Quintela]

>>>>> "robert" == Robert Love <rml@tech9.net> writes:

robert> On Wed, 2003-01-08 at 18:49, Juan Quintela wrote:
>> That is a nice theory, and I think that this could be true in the
>> past, but in 2.4.2X, PF_MEMDIE only appears in the two places that I
>> show, and it is completely redundant, look at the patch, we are just 
>> |-ing both PF_MEMALLOC and PF_MEMDIE and later we are &-ing against
>> the or of the two.  Use find & grep yourself if you don't believe me.

robert> I realize this.

robert> The issue is that PF_MEMALLOC can be _cleared_.  In that case, if you
robert> only set PF_MEMALLOC, that check can be false when we want it true.  So
robert> we need a flag that is more persistent.

robert> PF_MEMDIE, which is not cleared on various allocation paths in the VM,
robert> ensures that the check holds true for all OOM'ed tasks.

robert> I thought the same as you, "hey this thing is worthless let us dump it",
robert> and Rik and Andrew told me otherwise.

robert> I am not saying you are wrong, though - I could be very wrong.  But my
robert> point is not what you say above; it is that the flag is needed because
robert> just setting PF_MEMALLOC is insufficient since it can be unset.

I saw the light, thanks for the explanation.

Later, Juan.

-- 
In theory, practice and theory are the same, but in practice they 
are different -- Larry McVoy