diff mbox series

[v3,2/2] mm: collect the number of anon large folios partially mapped

Message ID 20240822224015.93186-3-21cnbao@gmail.com (mailing list archive)
State New
Headers show
Series mm: collect the number of anon mTHP | expand

Commit Message

Barry Song Aug. 22, 2024, 10:40 p.m. UTC 
From: Barry Song <v-songbaohua@oppo.com>

When an mTHP is added to the deferred_list due to partially mapped,
its partial pages are unused, leading to wasted memory and potentially
increasing memory reclamation pressure.

Detailing the specifics of how unmapping occurs is quite difficult
and not that useful, so we adopt a simple approach: each time an
mTHP enters the deferred_list, we increment the count by 1; whenever
it leaves for any reason, we decrement the count by 1.

Signed-off-by: Barry Song <v-songbaohua@oppo.com>
---
 Documentation/admin-guide/mm/transhuge.rst | 5 +++++
 include/linux/huge_mm.h                    | 1 +
 mm/huge_memory.c                           | 6 ++++++
 3 files changed, 12 insertions(+)

Comments

David Hildenbrand Aug. 23, 2024, 11:37 a.m. UTC | #1 
On 23.08.24 00:40, Barry Song wrote:
> From: Barry Song <v-songbaohua@oppo.com>
> 
> When an mTHP is added to the deferred_list due to partially mapped,
> its partial pages are unused, leading to wasted memory and potentially
> increasing memory reclamation pressure.
> 
> Detailing the specifics of how unmapping occurs is quite difficult
> and not that useful, so we adopt a simple approach: each time an
> mTHP enters the deferred_list, we increment the count by 1; whenever
> it leaves for any reason, we decrement the count by 1.

:) And here you only talk about mTHP but not in the subject.

> 
> Signed-off-by: Barry Song <v-songbaohua@oppo.com>
> ---
>   Documentation/admin-guide/mm/transhuge.rst | 5 +++++
>   include/linux/huge_mm.h                    | 1 +
>   mm/huge_memory.c                           | 6 ++++++
>   3 files changed, 12 insertions(+)
> 
> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
> index b78f2148b242..b1c948c7de9d 100644
> --- a/Documentation/admin-guide/mm/transhuge.rst
> +++ b/Documentation/admin-guide/mm/transhuge.rst
> @@ -556,6 +556,11 @@ nr_anon
>          These huge pages could be entirely mapped or have partially
>          unmapped/unused subpages.
>   
> +nr_anon_partially_mapped
> +       the number of transparent anon huge pages which have been partially
> +       unmapped and put onto split queue. Those unmapped subpages are
> +       also unused and temporarily wasting memory.

It's a bit more tricky I believe:

"the number of anonymous THP which are likely partially mapped, possibly 
wasting memory, and have been queued for deferred memory reclamation. 
Note that in corner some cases (e.g., failed migration), we might detect 
an anonymous THP as "partially mapped" and count it here, even though it 
is not actually partially mapped anymore."

Acked-by: David Hildenbrand <david@redhat.com>
diff mbox series

Patch

diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
index b78f2148b242..b1c948c7de9d 100644
--- a/Documentation/admin-guide/mm/transhuge.rst
+++ b/Documentation/admin-guide/mm/transhuge.rst
@@ -556,6 +556,11 @@  nr_anon
        These huge pages could be entirely mapped or have partially
        unmapped/unused subpages.
 
+nr_anon_partially_mapped
+       the number of transparent anon huge pages which have been partially
+       unmapped and put onto split queue. Those unmapped subpages are
+       also unused and temporarily wasting memory.
+
 As the system ages, allocating huge pages may be expensive as the
 system uses memory compaction to copy data around memory to free a
 huge page for use. There are some counters in ``/proc/vmstat`` to help
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 2ee2971e4e10..4ff4e7fedc95 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -127,6 +127,7 @@  enum mthp_stat_item {
 	MTHP_STAT_SPLIT_FAILED,
 	MTHP_STAT_SPLIT_DEFERRED,
 	MTHP_STAT_NR_ANON,
+	MTHP_STAT_NR_ANON_PARTIALLY_MAPPED,
 	__MTHP_STAT_COUNT
 };
 
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 26ad75fcda62..b5ee950df524 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -598,6 +598,7 @@  DEFINE_MTHP_STAT_ATTR(split, MTHP_STAT_SPLIT);
 DEFINE_MTHP_STAT_ATTR(split_failed, MTHP_STAT_SPLIT_FAILED);
 DEFINE_MTHP_STAT_ATTR(split_deferred, MTHP_STAT_SPLIT_DEFERRED);
 DEFINE_MTHP_STAT_ATTR(nr_anon, MTHP_STAT_NR_ANON);
+DEFINE_MTHP_STAT_ATTR(nr_anon_partially_mapped, MTHP_STAT_NR_ANON_PARTIALLY_MAPPED);
 
 static struct attribute *anon_stats_attrs[] = {
 	&anon_fault_alloc_attr.attr,
@@ -611,6 +612,7 @@  static struct attribute *anon_stats_attrs[] = {
 	&split_failed_attr.attr,
 	&split_deferred_attr.attr,
 	&nr_anon_attr.attr,
+	&nr_anon_partially_mapped_attr.attr,
 	NULL,
 };
 
@@ -3457,6 +3459,7 @@  int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
 		if (folio_order(folio) > 1 &&
 		    !list_empty(&folio->_deferred_list)) {
 			ds_queue->split_queue_len--;
+			mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
 			/*
 			 * Reinitialize page_deferred_list after removing the
 			 * page from the split_queue, otherwise a subsequent
@@ -3523,6 +3526,7 @@  void __folio_undo_large_rmappable(struct folio *folio)
 	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
 	if (!list_empty(&folio->_deferred_list)) {
 		ds_queue->split_queue_len--;
+		mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
 		list_del_init(&folio->_deferred_list);
 	}
 	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
@@ -3564,6 +3568,7 @@  void deferred_split_folio(struct folio *folio)
 		if (folio_test_pmd_mappable(folio))
 			count_vm_event(THP_DEFERRED_SPLIT_PAGE);
 		count_mthp_stat(folio_order(folio), MTHP_STAT_SPLIT_DEFERRED);
+		mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, 1);
 		list_add_tail(&folio->_deferred_list, &ds_queue->split_queue);
 		ds_queue->split_queue_len++;
 #ifdef CONFIG_MEMCG
@@ -3611,6 +3616,7 @@  static unsigned long deferred_split_scan(struct shrinker *shrink,
 			list_move(&folio->_deferred_list, &list);
 		} else {
 			/* We lost race with folio_put() */
+			mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
 			list_del_init(&folio->_deferred_list);
 			ds_queue->split_queue_len--;
 		}