[PATCH 0/2] x86: fix memory leaks when doing CPU hotplug

[PATCH 0/2] x86: fix memory leaks when doing CPU hotplug

[Andreas Herrmann]

Following patches fix two memory leaks with CPU hotplug.
Some per CPU data is allocated each time a CPU is set online.
But this space is never freed.

Usually this memory leak is not a big deal (for normal CPU hotplug usage).
But during stress tests with lots of CPU offline/online cycles this
really matters.

The entire leak is 40K (10 pages) for each offline/online cycle per
CPU.  I've verified both fixes performing more than 90000 CPU
offline/online cycles.

This is not a regression but I think it's still 2.6.27 material.
Please apply.


Regards,

Andreas


BTW, there is still a leak of about 600 bytes per offline/online cycle
per CPU -- according to slabinfo this might be sysfs related. The most
suspicious entries are:

Name                   Objects Objsize    Space Slabs/Part/Cpu  O/S O %Fr %Ef Flg
sysfs_dir_cache         266085      80    41.9M      10235/4/0   26 0   0  50 PZFU
kmalloc-8               130870       8    10.5M       2568/5/0   51 0   0   9 PZFU

[PATCH 1/2] x86: pda_init(): fix memory leak when using CPU hotplug

[Andreas Herrmann]

pda->irqstackptr is allocated whenever a CPU is set online.
But it is never freed. This results in a memory leak of 16K
for each CPU offline/online cycle.

Fix is to allocate pda->irqstackptr only once.

Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
---
 arch/x86/kernel/cpu/common_64.c |   15 +++++++++------
 1 files changed, 9 insertions(+), 6 deletions(-)

This is a re-submission of a patch posted last week. See
http://marc.info/?l=linux-kernel&m=121760147831093
Patch is against 2.6.27-rc2.

diff --git a/arch/x86/kernel/cpu/common_64.c b/arch/x86/kernel/cpu/common_64.c
index dd6e3f1..c941397 100644
--- a/arch/x86/kernel/cpu/common_64.c
+++ b/arch/x86/kernel/cpu/common_64.c
@@ -493,17 +493,20 @@ void pda_init(int cpu)
 		/* others are initialized in smpboot.c */
 		pda->pcurrent = &init_task;
 		pda->irqstackptr = boot_cpu_stack;
+		pda->irqstackptr += IRQSTACKSIZE - 64;
 	} else {
-		pda->irqstackptr = (char *)
-			__get_free_pages(GFP_ATOMIC, IRQSTACK_ORDER);
-		if (!pda->irqstackptr)
-			panic("cannot allocate irqstack for cpu %d", cpu);
+		if (!pda->irqstackptr) {
+			pda->irqstackptr = (char *)
+				__get_free_pages(GFP_ATOMIC, IRQSTACK_ORDER);
+			if (!pda->irqstackptr)
+				panic("cannot allocate irqstack for cpu %d",
+				      cpu);
+			pda->irqstackptr += IRQSTACKSIZE - 64;
+		}
 
 		if (pda->nodenumber == 0 && cpu_to_node(cpu) != NUMA_NO_NODE)
 			pda->nodenumber = cpu_to_node(cpu);
 	}
-
-	pda->irqstackptr += IRQSTACKSIZE-64;
 }
 
 char boot_exception_stacks[(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ +
-- 
1.5.6.4

[PATCH 2/2] x86: cpu_init(): fix memory leak when using CPU hotplug

[Andreas Herrmann]

Exception stacks are allocated each time a CPU is set online.
But the allocated space is never freed. Thus with one CPU hotplug
offline/online cycle there is a memory leak of 24K (6 pages) for
a CPU.

Fix is to allocate exception stacks only once -- when the CPU is
set online for the first time.

Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
---
 arch/x86/kernel/cpu/common_64.c |   23 +++++++++++++----------
 1 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/cpu/common_64.c b/arch/x86/kernel/cpu/common_64.c
index c941397..a5b9600 100644
--- a/arch/x86/kernel/cpu/common_64.c
+++ b/arch/x86/kernel/cpu/common_64.c
@@ -604,19 +604,22 @@ void __cpuinit cpu_init(void)
 	/*
 	 * set up and load the per-CPU TSS
 	 */
-	for (v = 0; v < N_EXCEPTION_STACKS; v++) {
+	if (!orig_ist->ist[0]) {
 		static const unsigned int order[N_EXCEPTION_STACKS] = {
-			[0 ... N_EXCEPTION_STACKS - 1] = EXCEPTION_STACK_ORDER,
-			[DEBUG_STACK - 1] = DEBUG_STACK_ORDER
+		  [0 ... N_EXCEPTION_STACKS - 1] = EXCEPTION_STACK_ORDER,
+		  [DEBUG_STACK - 1] = DEBUG_STACK_ORDER
 		};
-		if (cpu) {
-			estacks = (char *)__get_free_pages(GFP_ATOMIC, order[v]);
-			if (!estacks)
-				panic("Cannot allocate exception stack %ld %d\n",
-				      v, cpu);
+		for (v = 0; v < N_EXCEPTION_STACKS; v++) {
+			if (cpu) {
+				estacks = (char *)__get_free_pages(GFP_ATOMIC, order[v]);
+				if (!estacks)
+					panic("Cannot allocate exception "
+					      "stack %ld %d\n", v, cpu);
+			}
+			estacks += PAGE_SIZE << order[v];
+			orig_ist->ist[v] = t->x86_tss.ist[v] =
+					(unsigned long)estacks;
 		}
-		estacks += PAGE_SIZE << order[v];
-		orig_ist->ist[v] = t->x86_tss.ist[v] = (unsigned long)estacks;
 	}
 
 	t->x86_tss.io_bitmap_base = offsetof(struct tss_struct, io_bitmap);
-- 
1.5.6.4

Re: [PATCH 0/2] x86: fix memory leaks when doing CPU hotplug

[Ingo Molnar]

* Andreas Herrmann <andreas.herrmann3@amd.com> wrote:

> Following patches fix two memory leaks with CPU hotplug. Some per CPU 
> data is allocated each time a CPU is set online. But this space is 
> never freed.
> 
> Usually this memory leak is not a big deal (for normal CPU hotplug 
> usage). But during stress tests with lots of CPU offline/online cycles 
> this really matters.
> 
> The entire leak is 40K (10 pages) for each offline/online cycle per 
> CPU.  I've verified both fixes performing more than 90000 CPU 
> offline/online cycles.

applied to tip/x86/core, thanks Andreas.

> This is not a regression but I think it's still 2.6.27 material. 
> Please apply.

it's tricky code so i guess it's best to let it cook in tip/master a 
bit. If it does not show up upstream by say -rc4 time could you please 
ping us about it?

	Ingo

Re: [PATCH 0/2] x86: fix memory leaks when doing CPU hotplug

[Andreas Herrmann]

On Mon, Aug 11, 2008 at 09:40:15PM +0200, Ingo Molnar wrote:
> 
> * Andreas Herrmann <andreas.herrmann3@amd.com> wrote:
> 
> > Following patches fix two memory leaks with CPU hotplug. Some per CPU 
> > data is allocated each time a CPU is set online. But this space is 
> > never freed.
> > 
> > Usually this memory leak is not a big deal (for normal CPU hotplug 
> > usage). But during stress tests with lots of CPU offline/online cycles 
> > this really matters.
> > 
> > The entire leak is 40K (10 pages) for each offline/online cycle per 
> > CPU.  I've verified both fixes performing more than 90000 CPU 
> > offline/online cycles.
> 
> applied to tip/x86/core, thanks Andreas.
> 
> > This is not a regression but I think it's still 2.6.27 material. 
> > Please apply.
> 
> it's tricky code so i guess it's best to let it cook in tip/master a 
> bit. If it does not show up upstream by say -rc4 time could you please 
> ping us about it?

Ping!

It's -rc5 time and

b55793f7528ce1b73c25b3ac8a86a6cda2a0f9a4 (x86: cpu_init(): fix memory leak when using CPU hotplug)
49800efcb17afdf973f33e8aa8807b7f83993cc6 (x86: pda_init(): fix memory leak when using CPU hotplug)

are in tip/master but not yet upstream.


Regards,

Andreas