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We'll track the complete lifespan of an anon THP, starting when it becomes an anon THP ("large anon folio") (->mapping gets set), until it gets freed (->mapping gets cleared). Introduce a new "nr_anon" counter per THP size and adjust the corresponding counter in the following cases: * We allocate a new THP and call folio_add_new_anon_rmap() to map it the first time and turn it into an anon THP. * We split an anon THP into multiple smaller ones. * We migrate an anon THP, when we prepare the destination. * We free an anon THP back to the buddy. Note that AnonPages in /proc/meminfo currently tracks the total number of *mapped* anonymous *pages*, and therefore has slightly different semantics. In the future, we might also want to track "nr_anon_mapped" for each THP size, which might be helpful when comparing it to the number of allocated anon THPs (long-term pinning, stuck in swapcache, memory leaks, ...). Further note that for now, we only track anon THPs after they got their ->mapping set, for example via folio_add_new_anon_rmap(). If we would allocate some in the swapcache, they will only show up in the statistics for now after they have been mapped to user space the first time, where we call folio_add_new_anon_rmap(). Signed-off-by: Barry Song Acked-by: David Hildenbrand --- Documentation/admin-guide/mm/transhuge.rst | 5 +++++ include/linux/huge_mm.h | 15 +++++++++++++-- mm/huge_memory.c | 13 ++++++++++--- mm/migrate.c | 4 ++++ mm/page_alloc.c | 5 ++++- mm/rmap.c | 1 + 6 files changed, 37 insertions(+), 6 deletions(-) diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/adm= in-guide/mm/transhuge.rst index 79435c537e21..b78f2148b242 100644 --- a/Documentation/admin-guide/mm/transhuge.rst +++ b/Documentation/admin-guide/mm/transhuge.rst @@ -551,6 +551,11 @@ split_deferred it would free up some memory. Pages on split queue are going to be split under memory pressure, if splitting is possible. =20 +nr_anon + the number of transparent anon huge pages we have in the whole syst= em. + These huge pages could be entirely mapped or have partially + unmapped/unused subpages. + 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 4c32058cacfe..2ee2971e4e10 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -126,6 +126,7 @@ enum mthp_stat_item { MTHP_STAT_SPLIT, MTHP_STAT_SPLIT_FAILED, MTHP_STAT_SPLIT_DEFERRED, + MTHP_STAT_NR_ANON, __MTHP_STAT_COUNT }; =20 @@ -136,14 +137,24 @@ struct mthp_stat { =20 DECLARE_PER_CPU(struct mthp_stat, mthp_stats); =20 -static inline void count_mthp_stat(int order, enum mthp_stat_item item) +static inline void mod_mthp_stat(int order, enum mthp_stat_item item, int = delta) { if (order <=3D 0 || order > PMD_ORDER) return; =20 - this_cpu_inc(mthp_stats.stats[order][item]); + this_cpu_add(mthp_stats.stats[order][item], delta); +} + +static inline void count_mthp_stat(int order, enum mthp_stat_item item) +{ + mod_mthp_stat(order, item, 1); } + #else +static inline void mod_mthp_stat(int order, enum mthp_stat_item item, int = delta) +{ +} + static inline void count_mthp_stat(int order, enum mthp_stat_item item) { } diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 513e7c87efee..26ad75fcda62 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -597,6 +597,7 @@ DEFINE_MTHP_STAT_ATTR(shmem_fallback_charge, MTHP_STAT_= SHMEM_FALLBACK_CHARGE); 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); =20 static struct attribute *anon_stats_attrs[] =3D { &anon_fault_alloc_attr.attr, @@ -609,6 +610,7 @@ static struct attribute *anon_stats_attrs[] =3D { &split_attr.attr, &split_failed_attr.attr, &split_deferred_attr.attr, + &nr_anon_attr.attr, NULL, }; =20 @@ -3314,8 +3316,9 @@ int split_huge_page_to_list_to_order(struct page *pag= e, struct list_head *list, struct deferred_split *ds_queue =3D get_deferred_split_queue(folio); /* reset xarray order to new order after split */ XA_STATE_ORDER(xas, &folio->mapping->i_pages, folio->index, new_order); - struct anon_vma *anon_vma =3D NULL; + bool is_anon =3D folio_test_anon(folio); struct address_space *mapping =3D NULL; + struct anon_vma *anon_vma =3D NULL; int order =3D folio_order(folio); int extra_pins, ret; pgoff_t end; @@ -3327,7 +3330,7 @@ int split_huge_page_to_list_to_order(struct page *pag= e, struct list_head *list, if (new_order >=3D folio_order(folio)) return -EINVAL; =20 - if (folio_test_anon(folio)) { + if (is_anon) { /* order-1 is not supported for anonymous THP. */ if (new_order =3D=3D 1) { VM_WARN_ONCE(1, "Cannot split to order-1 folio"); @@ -3367,7 +3370,7 @@ int split_huge_page_to_list_to_order(struct page *pag= e, struct list_head *list, if (folio_test_writeback(folio)) return -EBUSY; =20 - if (folio_test_anon(folio)) { + if (is_anon) { /* * The caller does not necessarily hold an mmap_lock that would * prevent the anon_vma disappearing so we first we take a @@ -3480,6 +3483,10 @@ int split_huge_page_to_list_to_order(struct page *pa= ge, struct list_head *list, } } =20 + if (is_anon) { + mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1); + mod_mthp_stat(new_order, MTHP_STAT_NR_ANON, 1 << (order - new_order)); + } __split_huge_page(page, list, end, new_order); ret =3D 0; } else { diff --git a/mm/migrate.c b/mm/migrate.c index 4f55f4930fe8..3cc8555de6d6 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -450,6 +450,8 @@ static int __folio_migrate_mapping(struct address_space= *mapping, /* No turning back from here */ newfolio->index =3D folio->index; newfolio->mapping =3D folio->mapping; + if (folio_test_anon(folio) && folio_test_large(folio)) + mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON, 1); if (folio_test_swapbacked(folio)) __folio_set_swapbacked(newfolio); =20 @@ -474,6 +476,8 @@ static int __folio_migrate_mapping(struct address_space= *mapping, */ newfolio->index =3D folio->index; newfolio->mapping =3D folio->mapping; + if (folio_test_anon(folio) && folio_test_large(folio)) + mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON, 1); folio_ref_add(newfolio, nr); /* add cache reference */ if (folio_test_swapbacked(folio)) { __folio_set_swapbacked(newfolio); diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 8a67d760b71a..7dcb0713eb57 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1084,8 +1084,11 @@ __always_inline bool free_pages_prepare(struct page = *page, (page + i)->flags &=3D ~PAGE_FLAGS_CHECK_AT_PREP; } } - if (PageMappingFlags(page)) + if (PageMappingFlags(page)) { + if (PageAnon(page)) + mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1); 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Fri, 23 Aug 2024 18:05:16 -0700 (PDT) Received: from Barrys-MBP.hub ([2407:7000:8942:5500:8d8:dd4b:c921:b282]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-7cd9ad56c9fsm3274064a12.64.2024.08.23.18.05.10 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Fri, 23 Aug 2024 18:05:16 -0700 (PDT) From: Barry Song <21cnbao@gmail.com> To: akpm@linux-foundation.org, linux-mm@kvack.org Cc: baolin.wang@linux.alibaba.com, chrisl@kernel.org, david@redhat.com, hanchuanhua@oppo.com, ioworker0@gmail.com, kaleshsingh@google.com, kasong@tencent.com, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, usamaarif642@gmail.com, v-songbaohua@oppo.com, yuanshuai@oppo.com, ziy@nvidia.com Subject: [PATCH v4 2/2] mm: count the number of partially mapped anonymous THPs per size Date: Sat, 24 Aug 2024 13:04:41 +1200 Message-Id: <20240824010441.21308-3-21cnbao@gmail.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <20240824010441.21308-1-21cnbao@gmail.com> References: <20240824010441.21308-1-21cnbao@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Barry Song 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. Signed-off-by: Barry Song Acked-by: David Hildenbrand --- 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/adm= in-guide/mm/transhuge.rst index b78f2148b242..6630f2ed14ee 100644 --- a/Documentation/admin-guide/mm/transhuge.rst +++ b/Documentation/admin-guide/mm/transhuge.rst @@ -556,6 +556,13 @@ nr_anon These huge pages could be entirely mapped or have partially unmapped/unused subpages. =20 +nr_anon_partially_mapped + the number of anonymous THP which are likely partially mapped, poss= ibly + wasting memory, and have been queued for deferred memory reclamatio= n. + Note that in corner some cases (e.g., failed migration), we might d= etect + an anonymous THP as "partially mapped" and count it here, even thou= gh 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 }; =20 diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 26ad75fcda62..a81eab98d6b8 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_PARTIALL= Y_MAPPED); =20 static struct attribute *anon_stats_attrs[] =3D { &anon_fault_alloc_attr.attr, @@ -611,6 +612,7 @@ static struct attribute *anon_stats_attrs[] =3D { &split_failed_attr.attr, &split_deferred_attr.attr, &nr_anon_attr.attr, + &nr_anon_partially_mapped_attr.attr, NULL, }; =20 @@ -3457,6 +3459,7 @@ int split_huge_page_to_list_to_order(struct page *pag= e, 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 shrin= ker *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--; } --=20 2.39.3 (Apple Git-146)