From 8175ebfd302abe6fbdca9037f763ecbfdb8db572 Mon Sep 17 00:00:00 2001 From: Barry Song Date: Sat, 24 Aug 2024 13:04:41 +1200 Subject: [PATCH] mm: count the number of partially mapped anonymous THPs per size When a THP 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 a THP enters the deferred_list, we increment the count by 1; whenever it leaves for any reason, we decrement the count by 1. Link: https://lkml.kernel.org/r/20240824010441.21308-3-21cnbao@gmail.com Signed-off-by: Barry Song Acked-by: David Hildenbrand Cc: Baolin Wang Cc: Chris Li Cc: Chuanhua Han Cc: Kairui Song Cc: Kalesh Singh Cc: Lance Yang Cc: Ryan Roberts Cc: Shuai Yuan Cc: Usama Arif Cc: Zi Yan Signed-off-by: Andrew Morton --- Documentation/admin-guide/mm/transhuge.rst | 7 +++++++ include/linux/huge_mm.h | 1 + mm/huge_memory.c | 6 ++++++ 3 files changed, 14 insertions(+) diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst index d6874234a09a..56a086900651 100644 --- a/Documentation/admin-guide/mm/transhuge.rst +++ b/Documentation/admin-guide/mm/transhuge.rst @@ -556,6 +556,13 @@ nr_anon might be currently entirely mapped or have partially unmapped/unused subpages. +nr_anon_partially_mapped + 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. + 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..4902e2f7e896 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 ea57c51d478d..efc625086dc7 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, @@ -609,6 +610,7 @@ static struct attribute *anon_stats_attrs[] = { #endif &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--; } -- 2.49.0