Re: [PATCH 1/5] mm: Add __GFP_NO_OOM_KILL flag

Rafael J. Wysocki
2009-05-04T22:23:36Z

On Monday 04 May 2009, David Rientjes wrote:
> On Mon, 4 May 2009, Rafael J. Wysocki wrote:
>
> > Index: linux-2.6/mm/page_alloc.c
> > ===================================================================
> > --- linux-2.6.orig/mm/page_alloc.c
> > +++ linux-2.6/mm/page_alloc.c
> > @@ -1599,7 +1599,8 @@ nofail_alloc:
> > zonelist, high_zoneidx, alloc_flags);
> > if (page)
> > goto got_pg;
> > - } else if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY)) {
> > + } else if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY)
> > + && !(gfp_mask & __GFP_NO_OOM_KILL)) {
> > if (!try_set_zone_oom(zonelist, gfp_mask)) {
> > schedule_timeout_uninterruptible(1);
> > goto restart;
> > Index: linux-2.6/include/linux/gfp.h
> > ===================================================================
> > --- linux-2.6.orig/include/linux/gfp.h
> > +++ linux-2.6/include/linux/gfp.h
> > @@ -51,8 +51,9 @@ struct vm_area_struct;
> > #define __GFP_THISNODE ((__force gfp_t)0x40000u)/* No fallback, no policies */
> > #define __GFP_RECLAIMABLE ((__force gfp_t)0x80000u) /* Page is reclaimable */
> > #define __GFP_MOVABLE ((__force gfp_t)0x100000u) /* Page is movable */
> > +#define __GFP_NO_OOM_KILL ((__force gfp_t)0x200000u) /* Don't invoke out_of_memory() */
> >
> > -#define __GFP_BITS_SHIFT 21 /* Room for 21 __GFP_FOO bits */
> > +#define __GFP_BITS_SHIFT 22 /* Number of __GFP_FOO bits */
> > #define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1))
> >
> > /* This equals 0, but use constants in case they ever change */
> >
>
> Yeah, that's much better, thanks. There's currently concerns about adding
> a new gfp flag in another thread (__GFP_PANIC), though, so you might find
> some resistance in adding a flag with a very specific and limited use cae.

Oh great. Andrew, what's your opinion?

> I think you might have better luck in doing
>
> struct zone *z;
>
> for_each_populated_zone(z)
> zone_set_flag(z, ZONE_OOM_LOCKED);
>
> if all other tasks are really in D state at this point since oom killer
> serialization is done with try locks in the page allocator.

Not all of them, actually. Some kernel threads are not freezable.

> This is equivalent to __GFP_NO_OOM_KILL.

In that case I think I'd go back to my initial idea with disabling the OOM
killer after freezing tasks.

Roughly, this. [The idea is that the OOM killer is not really going to work
while tasks are frozen, so we can just give up calling it in that case.]

---
include/linux/freezer.h | 2 ++
kernel/power/process.c | 12 ++++++++++++
mm/page_alloc.c | 4 +++-
3 files changed, 17 insertions(+), 1 deletion(-)

Index: linux-2.6/kernel/power/process.c
===================================================================
--- linux-2.6.orig/kernel/power/process.c
+++ linux-2.6/kernel/power/process.c
@@ -19,6 +19,8 @@
*/
#define TIMEOUT (20 * HZ)

+static bool tasks_frozen;
+
static inline int freezeable(struct task_struct * p)
{
if ((p == current) ||
@@ -120,6 +122,10 @@ int freeze_processes(void)
Exit:
BUG_ON(in_atomic());
printk("\n");
+
+ if (!error)
+ tasks_frozen = true;
+
return error;
}

@@ -145,6 +151,8 @@ static void thaw_tasks(bool nosig_only)

void thaw_processes(void)
{
+ tasks_frozen = false;
+
printk("Restarting tasks ... ");
thaw_tasks(true);
thaw_tasks(false);
@@ -152,3 +160,7 @@ void thaw_processes(void)
printk("done.\n");
}

+bool processes_are_frozen(void)
+{
+ return tasks_frozen;
+}
Index: linux-2.6/include/linux/freezer.h
===================================================================
--- linux-2.6.orig/include/linux/freezer.h
+++ linux-2.6/include/linux/freezer.h
@@ -50,6 +50,7 @@ extern int thaw_process(struct task_stru
extern void refrigerator(void);
extern int freeze_processes(void);
extern void thaw_processes(void);
+extern bool processes_are_frozen(void);

static inline int try_to_freeze(void)
{
@@ -170,6 +171,7 @@ static inline int thaw_process(struct ta
static inline void refrigerator(void) {}
static inline int freeze_processes(void) { BUG(); return 0; }
static inline void thaw_processes(void) {}
+static inline bool processes_are_frozen(void) { return false; }

static inline int try_to_freeze(void) { return 0; }

Index: linux-2.6/mm/page_alloc.c
===================================================================
--- linux-2.6.orig/mm/page_alloc.c
+++ linux-2.6/mm/page_alloc.c
@@ -46,6 +46,7 @@
#include <linux/page-isolation.h>
#include <linux/page_cgroup.h>
#include <linux/debugobjects.h>
+#include <linux/freezer.h>

#include <asm/tlbflush.h>
#include <asm/div64.h>
@@ -1599,7 +1600,8 @@ nofail_alloc:
zonelist, high_zoneidx, alloc_flags);
if (page)
goto got_pg;
- } else if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY)) {
+ } else if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY)
+ && !processes_are_frozen()) {
if (!try_set_zone_oom(zonelist, gfp_mask)) {
schedule_timeout_uninterruptible(1);
goto restart;