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Wed, 22 Oct 2025 14:39:56 -0400 X-MC-Unique: 16FQH2eaOmWNqsjZWIxpBg-1 X-Mimecast-MFC-AGG-ID: 16FQH2eaOmWNqsjZWIxpBg_1761158391 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 7BE9E19560B3; Wed, 22 Oct 2025 18:39:51 +0000 (UTC) Received: from h1.redhat.com (unknown [10.22.64.41]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 55D0C19560B4; Wed, 22 Oct 2025 18:39:42 +0000 (UTC) From: Nico Pache To: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org Cc: david@redhat.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, dev.jain@arm.com, corbet@lwn.net, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, akpm@linux-foundation.org, baohua@kernel.org, willy@infradead.org, peterx@redhat.com, wangkefeng.wang@huawei.com, usamaarif642@gmail.com, sunnanyong@huawei.com, vishal.moola@gmail.com, thomas.hellstrom@linux.intel.com, yang@os.amperecomputing.com, kas@kernel.org, aarcange@redhat.com, raquini@redhat.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, tiwai@suse.de, will@kernel.org, dave.hansen@linux.intel.com, jack@suse.cz, cl@gentwo.org, jglisse@google.com, surenb@google.com, zokeefe@google.com, hannes@cmpxchg.org, rientjes@google.com, mhocko@suse.com, rdunlap@infradead.org, hughd@google.com, richard.weiyang@gmail.com, lance.yang@linux.dev, vbabka@suse.cz, rppt@kernel.org, jannh@google.com, pfalcato@suse.de Subject: [PATCH v12 mm-new 09/15] khugepaged: add per-order mTHP collapse failure statistics Date: Wed, 22 Oct 2025 12:37:11 -0600 Message-ID: <20251022183717.70829-10-npache@redhat.com> In-Reply-To: <20251022183717.70829-1-npache@redhat.com> References: <20251022183717.70829-1-npache@redhat.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Add three new mTHP statistics to track collapse failures for different orders when encountering swap PTEs, excessive none PTEs, and shared PTEs: - collapse_exceed_swap_pte: Increment when mTHP collapse fails due to swap PTEs - collapse_exceed_none_pte: Counts when mTHP collapse fails due to exceeding the none PTE threshold for the given order - collapse_exceed_shared_pte: Counts when mTHP collapse fails due to shared PTEs These statistics complement the existing THP_SCAN_EXCEED_* events by providing per-order granularity for mTHP collapse attempts. The stats are exposed via sysfs under `/sys/kernel/mm/transparent_hugepage/hugepages-*/stats/` for each supported hugepage size. As we currently dont support collapsing mTHPs that contain a swap or shared entry, those statistics keep track of how often we are encountering failed mTHP collapses due to these restrictions. Reviewed-by: Baolin Wang Signed-off-by: Nico Pache --- Documentation/admin-guide/mm/transhuge.rst | 23 ++++++++++++++++++++++ include/linux/huge_mm.h | 3 +++ mm/huge_memory.c | 7 +++++++ mm/khugepaged.c | 16 ++++++++++++--- 4 files changed, 46 insertions(+), 3 deletions(-) diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst index 13269a0074d4..7c71cda8aea1 100644 --- a/Documentation/admin-guide/mm/transhuge.rst +++ b/Documentation/admin-guide/mm/transhuge.rst @@ -709,6 +709,29 @@ nr_anon_partially_mapped an anonymous THP as "partially mapped" and count it here, even though it is not actually partially mapped anymore. +collapse_exceed_none_pte + The number of anonymous mTHP pte ranges where the number of none PTEs + exceeded the max_ptes_none threshold. For mTHP collapse, khugepaged + checks a PMD region and tracks which PTEs are present. It then tries + to collapse to the largest enabled mTHP size. The allowed number of empty + PTEs is the max_ptes_none threshold scaled by the collapse order. This + counter records the number of times a collapse attempt was skipped for + this reason, and khugepaged moved on to try the next available mTHP size. + +collapse_exceed_swap_pte + The number of anonymous mTHP pte ranges which contain at least one swap + PTE. Currently khugepaged does not support collapsing mTHP regions + that contain a swap PTE. This counter can be used to monitor the + number of khugepaged mTHP collapses that failed due to the presence + of a swap PTE. + +collapse_exceed_shared_pte + The number of anonymous mTHP pte ranges which contain at least one shared + PTE. Currently khugepaged does not support collapsing mTHP pte ranges + that contain a shared PTE. This counter can be used to monitor the + number of khugepaged mTHP collapses that failed due to the presence + of a shared PTE. + 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 3d29624c4f3f..4b2773235041 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -144,6 +144,9 @@ enum mthp_stat_item { MTHP_STAT_SPLIT_DEFERRED, MTHP_STAT_NR_ANON, MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, + MTHP_STAT_COLLAPSE_EXCEED_SWAP, + MTHP_STAT_COLLAPSE_EXCEED_NONE, + MTHP_STAT_COLLAPSE_EXCEED_SHARED, __MTHP_STAT_COUNT }; diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 0063d1ba926e..7335b92969d6 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -638,6 +638,10 @@ 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); +DEFINE_MTHP_STAT_ATTR(collapse_exceed_swap_pte, MTHP_STAT_COLLAPSE_EXCEED_SWAP); +DEFINE_MTHP_STAT_ATTR(collapse_exceed_none_pte, MTHP_STAT_COLLAPSE_EXCEED_NONE); +DEFINE_MTHP_STAT_ATTR(collapse_exceed_shared_pte, MTHP_STAT_COLLAPSE_EXCEED_SHARED); + static struct attribute *anon_stats_attrs[] = { &anon_fault_alloc_attr.attr, @@ -654,6 +658,9 @@ static struct attribute *anon_stats_attrs[] = { &split_deferred_attr.attr, &nr_anon_attr.attr, &nr_anon_partially_mapped_attr.attr, + &collapse_exceed_swap_pte_attr.attr, + &collapse_exceed_none_pte_attr.attr, + &collapse_exceed_shared_pte_attr.attr, NULL, }; diff --git a/mm/khugepaged.c b/mm/khugepaged.c index d741af15e18c..053202141ea3 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -592,7 +592,9 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, continue; } else { result = SCAN_EXCEED_NONE_PTE; - count_vm_event(THP_SCAN_EXCEED_NONE_PTE); + if (order == HPAGE_PMD_ORDER) + count_vm_event(THP_SCAN_EXCEED_NONE_PTE); + count_mthp_stat(order, MTHP_STAT_COLLAPSE_EXCEED_NONE); goto out; } } @@ -622,10 +624,17 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, * shared may cause a future higher order collapse on a * rescan of the same range. */ - if (order != HPAGE_PMD_ORDER || (cc->is_khugepaged && - shared > khugepaged_max_ptes_shared)) { + if (order != HPAGE_PMD_ORDER) { + result = SCAN_EXCEED_SHARED_PTE; + count_mthp_stat(order, MTHP_STAT_COLLAPSE_EXCEED_SHARED); + goto out; + } + + if (cc->is_khugepaged && + shared > khugepaged_max_ptes_shared) { result = SCAN_EXCEED_SHARED_PTE; count_vm_event(THP_SCAN_EXCEED_SHARED_PTE); + count_mthp_stat(order, MTHP_STAT_COLLAPSE_EXCEED_SHARED); goto out; } } @@ -1073,6 +1082,7 @@ static int __collapse_huge_page_swapin(struct mm_struct *mm, * range. */ if (order != HPAGE_PMD_ORDER) { + count_mthp_stat(order, MTHP_STAT_COLLAPSE_EXCEED_SWAP); pte_unmap(pte); mmap_read_unlock(mm); result = SCAN_EXCEED_SWAP_PTE; -- 2.51.0