[PATCH v2 0/4] track memory used by balloon drivers

[PATCH v2 0/4] track memory used by balloon drivers

[Nico Pache]

This series introduces a way to track memory used by balloon drivers.

Add a NR_BALLOON_PAGES counter to track how many pages are reclaimed by the
balloon drivers. First add the accounting, then updates the balloon drivers
(virtio, Hyper-V, VMware, Pseries-cmm, and Xen) to maintain this counter. The
virtio, Vmware, and pseries-cmm balloon drivers utilize the balloon_compaction
interface to allocate and free balloon pages. Other balloon drivers will have to
maintain this counter manually.

This makes the information visible in memory reporting interfaces like
/proc/meminfo, show_mem, and OOM reporting.

This provides admins visibility into their VM balloon sizes without
requiring different virtualization tooling. Furthermore, this information
is helpful when debugging an OOM inside a VM.

V2 changes:
- Add counter to the balloon_compaction interface
- Dropped patches for virtio and VMware as they use balloon_compaction interface

Tested: virtio_balloon, run stress-ng, inflate balloon, oom prints
Signed-off-by: Nico Pache <npache@redhat.com>

Nico Pache (4):
  meminfo: add a per node counter for balloon drivers
  balloon_compaction: update the NR_BALLOON_PAGES state
  hv_balloon: update the NR_BALLOON_PAGES state
  xen: balloon: update the NR_BALLOON_PAGES state

 drivers/hv/hv_balloon.c | 2 ++
 drivers/xen/balloon.c   | 4 ++++
 fs/proc/meminfo.c       | 2 ++
 include/linux/mmzone.h  | 1 +
 mm/balloon_compaction.c | 2 ++
 mm/show_mem.c           | 4 +++-
 mm/vmstat.c             | 1 +
 7 files changed, 15 insertions(+), 1 deletion(-)

-- 
2.48.1

[PATCH v2 1/4] meminfo: add a per node counter for balloon drivers

[Nico Pache]

Add NR_BALLOON_PAGES counter to track memory used by balloon drivers and
expose it through /proc/meminfo and other memory reporting interfaces.

Signed-off-by: Nico Pache <npache@redhat.com>
---
 fs/proc/meminfo.c      | 2 ++
 include/linux/mmzone.h | 1 +
 mm/show_mem.c          | 4 +++-
 mm/vmstat.c            | 1 +
 4 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
index 8ba9b1472390..83be312159c9 100644
--- a/fs/proc/meminfo.c
+++ b/fs/proc/meminfo.c
@@ -162,6 +162,8 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
 	show_val_kb(m, "Unaccepted:     ",
 		    global_zone_page_state(NR_UNACCEPTED));
 #endif
+	show_val_kb(m, "Balloon:        ",
+		    global_node_page_state(NR_BALLOON_PAGES));
 
 	hugetlb_report_meminfo(m);
 
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 9540b41894da..71d3ff19267a 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -223,6 +223,7 @@ enum node_stat_item {
 #ifdef CONFIG_HUGETLB_PAGE
 	NR_HUGETLB,
 #endif
+	NR_BALLOON_PAGES,
 	NR_VM_NODE_STAT_ITEMS
 };
 
diff --git a/mm/show_mem.c b/mm/show_mem.c
index 43afb56abbd3..6af13bcd2ab3 100644
--- a/mm/show_mem.c
+++ b/mm/show_mem.c
@@ -260,6 +260,7 @@ static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_z
 			" pagetables:%lukB"
 			" sec_pagetables:%lukB"
 			" all_unreclaimable? %s"
+			" Balloon:%lukB"
 			"\n",
 			pgdat->node_id,
 			K(node_page_state(pgdat, NR_ACTIVE_ANON)),
@@ -285,7 +286,8 @@ static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_z
 #endif
 			K(node_page_state(pgdat, NR_PAGETABLE)),
 			K(node_page_state(pgdat, NR_SECONDARY_PAGETABLE)),
-			str_yes_no(pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES));
+			str_yes_no(pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES),
+			K(node_page_state(pgdat, NR_BALLOON_PAGES)));
 	}
 
 	for_each_populated_zone(zone) {
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 16bfe1c694dd..d3b11891a942 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1276,6 +1276,7 @@ const char * const vmstat_text[] = {
 #ifdef CONFIG_HUGETLB_PAGE
 	"nr_hugetlb",
 #endif
+	"nr_balloon_pages",
 	/* system-wide enum vm_stat_item counters */
 	"nr_dirty_threshold",
 	"nr_dirty_background_threshold",
-- 
2.48.1

[PATCH v2 2/4] balloon_compaction: update the NR_BALLOON_PAGES state

[Nico Pache]

Update the NR_BALLOON_PAGES counter when pages are added or removed using
the balloon compaction interface.

The virtio, Vmware, and pseries-cmm balloon drivers utilize the
balloon_compaction interface to allocate and free balloon pages. Other
balloon drivers will have to maintain this counter manually.

Signed-off-by: Nico Pache <npache@redhat.com>
---
 mm/balloon_compaction.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index 6597ebea8ae2..d3e00731e262 100644
--- a/mm/balloon_compaction.c
+++ b/mm/balloon_compaction.c
@@ -24,6 +24,7 @@ static void balloon_page_enqueue_one(struct balloon_dev_info *b_dev_info,
 	balloon_page_insert(b_dev_info, page);
 	unlock_page(page);
 	__count_vm_event(BALLOON_INFLATE);
+	inc_node_page_state(page, NR_BALLOON_PAGES);
 }
 
 /**
@@ -103,6 +104,7 @@ size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
 		__count_vm_event(BALLOON_DEFLATE);
 		list_add(&page->lru, pages);
 		unlock_page(page);
+		dec_node_page_state(page, NR_BALLOON_PAGES);
 		n_pages++;
 	}
 	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
-- 
2.48.1

[PATCH v2 3/4] hv_balloon: update the NR_BALLOON_PAGES state

[Nico Pache]

Update the NR_BALLOON_PAGES counter when pages are added to or
removed from the Hyper-V balloon.

Signed-off-by: Nico Pache <npache@redhat.com>
---
 drivers/hv/hv_balloon.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index fec2f18679e3..2b4080e51f97 100644
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -1192,6 +1192,7 @@ static void free_balloon_pages(struct hv_dynmem_device *dm,
 		__ClearPageOffline(pg);
 		__free_page(pg);
 		dm->num_pages_ballooned--;
+		mod_node_page_state(page_pgdat(pg), NR_BALLOON_PAGES, -1);
 		adjust_managed_page_count(pg, 1);
 	}
 }
@@ -1221,6 +1222,7 @@ static unsigned int alloc_balloon_pages(struct hv_dynmem_device *dm,
 			return i * alloc_unit;
 
 		dm->num_pages_ballooned += alloc_unit;
+		mod_node_page_state(page_pgdat(pg), NR_BALLOON_PAGES, alloc_unit);
 
 		/*
 		 * If we allocatted 2M pages; split them so we
-- 
2.48.1

[PATCH v2 4/4] xen: balloon: update the NR_BALLOON_PAGES state

[Nico Pache]

Update the NR_BALLOON_PAGES counter when pages are added to or
removed from the Xen balloon.

Signed-off-by: Nico Pache <npache@redhat.com>
---
 drivers/xen/balloon.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 163f7f1d70f1..65d4e7fa1eb8 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -157,6 +157,8 @@ static void balloon_append(struct page *page)
 		list_add(&page->lru, &ballooned_pages);
 		balloon_stats.balloon_low++;
 	}
+	inc_node_page_state(page, NR_BALLOON_PAGES);
+
 	wake_up(&balloon_wq);
 }
 
@@ -179,6 +181,8 @@ static struct page *balloon_retrieve(bool require_lowmem)
 		balloon_stats.balloon_low--;
 
 	__ClearPageOffline(page);
+	dec_node_page_state(page, NR_BALLOON_PAGES);
+
 	return page;
 }
 
-- 
2.48.1

Re: [PATCH v2 1/4] meminfo: add a per node counter for balloon drivers

[Andrew Morton]

On Fri, 14 Mar 2025 15:37:54 -0600 Nico Pache <npache@redhat.com> wrote:

> Add NR_BALLOON_PAGES counter to track memory used by balloon drivers and
> expose it through /proc/meminfo and other memory reporting interfaces.
> 
> ...
>
> --- a/fs/proc/meminfo.c
> +++ b/fs/proc/meminfo.c
> @@ -162,6 +162,8 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
>  	show_val_kb(m, "Unaccepted:     ",
>  		    global_zone_page_state(NR_UNACCEPTED));
>  #endif
> +	show_val_kb(m, "Balloon:        ",
> +		    global_node_page_state(NR_BALLOON_PAGES));

Please update Documentation/filesystems/proc.rst for this.

RE: [PATCH v2 3/4] hv_balloon: update the NR_BALLOON_PAGES state

[Michael Kelley]

From: Nico Pache <npache@redhat.com> Sent: Friday, March 14, 2025 2:38 PM
> 
> Update the NR_BALLOON_PAGES counter when pages are added to or
> removed from the Hyper-V balloon.
> 
> Signed-off-by: Nico Pache <npache@redhat.com>
> ---
>  drivers/hv/hv_balloon.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
> index fec2f18679e3..2b4080e51f97 100644
> --- a/drivers/hv/hv_balloon.c
> +++ b/drivers/hv/hv_balloon.c
> @@ -1192,6 +1192,7 @@ static void free_balloon_pages(struct hv_dynmem_device *dm,
>  		__ClearPageOffline(pg);
>  		__free_page(pg);
>  		dm->num_pages_ballooned--;
> +		mod_node_page_state(page_pgdat(pg), NR_BALLOON_PAGES, -1);
>  		adjust_managed_page_count(pg, 1);
>  	}
>  }
> @@ -1221,6 +1222,7 @@ static unsigned int alloc_balloon_pages(struct hv_dynmem_device *dm,
>  			return i * alloc_unit;
> 
>  		dm->num_pages_ballooned += alloc_unit;
> +		mod_node_page_state(page_pgdat(pg), NR_BALLOON_PAGES, alloc_unit);
> 
>  		/*
>  		 * If we allocatted 2M pages; split them so we
> --
> 2.48.1
> 

As is evident from the code, the hv_balloon driver already has accounting
for the number of pages that have been ballooned out of the VM. This
accounting and other details of the hv_balloon driver state is available in
/sys/kernel/debug/hv-balloon when CONFIG_DEBUGFS=y. But it seems OK
to also report the # of pages ballooned through /proc/meminfo, which
works even if CONFIG_DEBUGFS=n.

Reviewed-by: Michael Kelley <mhklinux@outlook.com>

Re: [PATCH v2 1/4] meminfo: add a per node counter for balloon drivers

[Nico Pache]

On 3/14/25 7:06 PM, Andrew Morton wrote:
> On Fri, 14 Mar 2025 15:37:54 -0600 Nico Pache <npache@redhat.com> wrote:
> 
>> Add NR_BALLOON_PAGES counter to track memory used by balloon drivers and
>> expose it through /proc/meminfo and other memory reporting interfaces.
>>
>> ...
>>
>> --- a/fs/proc/meminfo.c
>> +++ b/fs/proc/meminfo.c
>> @@ -162,6 +162,8 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
>>  	show_val_kb(m, "Unaccepted:     ",
>>  		    global_zone_page_state(NR_UNACCEPTED));
>>  #endif
>> +	show_val_kb(m, "Balloon:        ",
>> +		    global_node_page_state(NR_BALLOON_PAGES));
> 
> Please update Documentation/filesystems/proc.rst for this.

@Andrew

Can you please squash the following?

From b1b379a32752e64c60b5e3b6365c93db8e1daf9f Mon Sep 17 00:00:00 2001
From: Nico Pache <npache@redhat.com>
Date: Mon, 17 Mar 2025 16:07:18 -0600
Subject: [PATCH] Documentation: document Balloon Meminfo entry

Add a Balloon entry to the Meminfo documention.

Signed-off-by: Nico Pache <npache@redhat.com>
---
 Documentation/filesystems/proc.rst | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index 09f0aed5a08b..2868bb74f76e 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -1060,6 +1060,7 @@ Example output. You may not have all of these fields.
     FilePmdMapped:         0 kB
     CmaTotal:              0 kB
     CmaFree:               0 kB
+    Balloon:               0 kB
     HugePages_Total:       0
     HugePages_Free:        0
     HugePages_Rsvd:        0
@@ -1228,6 +1229,8 @@ CmaTotal
               Memory reserved for the Contiguous Memory Allocator (CMA)
 CmaFree
               Free remaining memory in the CMA reserves
+Balloon
+              Memory returned to Host by VM Balloon Drivers
 HugePages_Total, HugePages_Free, HugePages_Rsvd, HugePages_Surp, Hugepagesize,
Hugetlb
               See Documentation/admin-guide/mm/hugetlbpage.rst.
 DirectMap4k, DirectMap2M, DirectMap1G
-- 
2.48.1
> 

Re: [PATCH v2 4/4] xen: balloon: update the NR_BALLOON_PAGES state

[Jürgen Groß]

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On 14.03.25 22:37, Nico Pache wrote:
> Update the NR_BALLOON_PAGES counter when pages are added to or
> removed from the Xen balloon.
> 
> Signed-off-by: Nico Pache <npache@redhat.com>

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen

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