[patch] 2.5: kill PF_MEMDIE

[patch] 2.5: kill PF_MEMDIE

[Robert Love]

PF_MEMDIE seems to serve no needed purpose in 2.5.  In fact, it seems it
has no point in 2.4, either.

Attached patch, against 2.5.49-mm1, makes PF_MEMDIE die.

	Robert Love


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


diff -urN linux-2.5.49-mm1/include/linux/sched.h linux/include/linux/sched.h
--- linux-2.5.49-mm1/include/linux/sched.h	2002-11-25 01:06:22.000000000 -0500
+++ linux/include/linux/sched.h	2002-11-25 00:54:12.000000000 -0500
@@ -421,7 +421,6 @@
 #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_FLUSHER	0x00002000	/* responsible for disk writeback */
 #define PF_NOWARN	0x00004000	/* debug: don't warn if alloc fails */
 
diff -urN linux-2.5.49-mm1/mm/oom_kill.c linux/mm/oom_kill.c
--- linux-2.5.49-mm1/mm/oom_kill.c	2002-11-25 01:13:53.000000000 -0500
+++ linux/mm/oom_kill.c	2002-11-25 01:05:08.000000000 -0500
@@ -146,7 +146,7 @@
 	 * exit() and clear out its resources quickly...
 	 */
 	p->time_slice = 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 -urN linux-2.5.49-mm1/mm/page_alloc.c linux/mm/page_alloc.c
--- linux-2.5.49-mm1/mm/page_alloc.c	2002-11-25 01:13:53.000000000 -0500
+++ linux/mm/page_alloc.c	2002-11-25 00:55:39.000000000 -0500
@@ -613,7 +613,7 @@
 	/* here we're in the low on memory slow path */
 
 rebalance:
-	if ((current->flags & (PF_MEMALLOC | PF_MEMDIE)) && !in_interrupt()) {
+	if ((current->flags & PF_MEMALLOC) && !in_interrupt()) {
 		/* go through the zonelist yet again, ignoring mins */
 		for (i = 0; zones[i] != NULL; i++) {
 			struct zone *z = zones[i];

Re: [patch] 2.5: kill PF_MEMDIE

[Hugh Dickins]

On 25 Nov 2002, Robert Love wrote:

> PF_MEMDIE seems to serve no needed purpose in 2.5.  In fact, it seems it
> has no point in 2.4, either.
> 
> Attached patch, against 2.5.49-mm1, makes PF_MEMDIE die.

What makes you say no needed purpose?  I agree it's screwed in 2.5,
but its purpose is to make more memory available to the OOMkilled task,
so it's not held up on its way out to freeing memory: seems reasonable.

I'm no great lover of PF_MEMDIE and PF_ flag manipulation, but let it
live until we have an alternative?  I think the better patch is not
to lose PF_MEMDIE (and conceivably others) once it has been set.

(Shall we agree to turn a blind eye to the risk of oom_kill_task
manipulating p->flags while it may be another CPU's current->flags?)

Hugh

--- 2.5.49-mm1/mm/page_alloc.c	Sat Nov 23 10:18:53 2002
+++ linux/mm/page_alloc.c	Mon Nov 25 11:54:27 2002
@@ -432,7 +432,8 @@
 
 	current->flags |= PF_MEMALLOC;
 	ret = try_to_free_pages(classzone, gfp_flags, order);
-	current->flags = cflags;
+	if (!(cflags & PF_MEMALLOC))
+		current->flags &= ~PF_MEMALLOC;
 	return ret;
 }
 
--- 2.5.49-mm1/mm/swap_state.c	Tue Nov  5 00:03:10 2002
+++ linux/mm/swap_state.c	Mon Nov 25 12:08:40 2002
@@ -120,6 +120,7 @@
 {
 	swp_entry_t entry;
 	int pf_flags;
+	int err;
 
 	if (!PageLocked(page))
 		BUG();
@@ -149,9 +150,15 @@
 		/*
 		 * Add it to the swap cache and mark it dirty
 		 */
-		switch (add_to_page_cache(page, &swapper_space, entry.val)) {
+		err = add_to_page_cache(page, &swapper_space, entry.val);
+
+		if (!(pf_flags & PF_NOWARN))
+			current->flags &= ~PF_NOWARN;
+		if (pf_flags & PF_MEMALLOC)
+			current->flags |= PF_MEMALLOC;
+
+		switch (err) {
 		case 0:				/* Success */
-			current->flags = pf_flags;
 			SetPageUptodate(page);
 			ClearPageDirty(page);
 			set_page_dirty(page);
@@ -159,13 +166,11 @@
 			return 1;
 		case -EEXIST:
 			/* Raced with "speculative" read_swap_cache_async */
-			current->flags = pf_flags;
 			INC_CACHE_INFO(exist_race);
 			swap_free(entry);
 			continue;
 		default:
 			/* -ENOMEM radix-tree allocation failure */
-			current->flags = pf_flags;
 			swap_free(entry);
 			return 0;
 		}

Re: [patch] 2.5: kill PF_MEMDIE

[Rik van Riel]

On 25 Nov 2002, Robert Love wrote:

> PF_MEMDIE seems to serve no needed purpose in 2.5.  In fact, it seems it
> has no point in 2.4, either.

Actually it does. If the task that's being OOM killed is in
try_to_free_pages() it'll clear PF_MEMALLOC before going back
into __alloc_pages() and it might not die.

Rik
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