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Thu, 26 Feb 2026 03:25:16 +0000 (UTC) Received: from h1.redhat.com (unknown [10.22.64.173]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 983A73003D88; Thu, 26 Feb 2026 03:25:06 +0000 (UTC) From: Nico Pache To: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org Cc: aarcange@redhat.com, akpm@linux-foundation.org, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, catalin.marinas@arm.com, cl@gentwo.org, corbet@lwn.net, dave.hansen@linux.intel.com, david@kernel.org, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jack@suse.cz, jackmanb@google.com, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, lance.yang@linux.dev, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, npache@redhat.com, peterx@redhat.com, pfalcato@suse.de, rakie.kim@sk.com, raquini@redhat.com, rdunlap@infradead.org, richard.weiyang@gmail.com, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, ryan.roberts@arm.com, shivankg@amd.com, sunnanyong@huawei.com, surenb@google.com, thomas.hellstrom@linux.intel.com, tiwai@suse.de, usamaarif642@gmail.com, vbabka@suse.cz, vishal.moola@gmail.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yang@os.amperecomputing.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, zokeefe@google.com Subject: [PATCH mm-unstable v15 07/13] mm/khugepaged: add per-order mTHP collapse failure statistics Date: Wed, 25 Feb 2026 20:25:04 -0700 Message-ID: <20260226032504.233594-1-npache@redhat.com> In-Reply-To: <20260226031741.230674-1-npache@redhat.com> References: <20260226031741.230674-1-npache@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: dOc6dvWIj9RemjiAJDmO8ubYbOEYC8IzLnF3Ug18Kvs_1772076316 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true X-Rspamd-Server: rspam05 X-Rspam-User: X-Rspamd-Queue-Id: 31988140008 X-Stat-Signature: dnbqqratz5fdp5nxndxqj7jc9n1e1qc5 X-HE-Tag: 1772076328-247906 X-HE-Meta: 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 DpPzRxo/ DAmgUEBRhEf2ULl9IP8MxMGmMR7njOlN9ZsiUrVEO1U+S+ILhxNVvxmMtWs5l0eTcmsMV1sK8ehxfzi8XwcOLVohZxd0rUF19erSV4uuXZuqYDOWTtgnxvOstaWjBnb15HHqRS9slqToCTcQz0JFdkVN9/oU2Q81fgOxZfNsJBlke4UDSrU+gkNWlP/pOG+kXktnrwnhtkotfA8eUKwQgjB3q3GEIpvkYv+xQFnTXlw+xd4E2ZHIxisSGBa3f/UdP2sE6HkD8+SnqKYgQmaaqGyLpk8f6y0luvqaXPfHJvpSQ0RgtSmdIu1WsZpZFx8eju+cQ/mdP6ApTd8abYuDtPxHUgv/OkxrFUqdxGlbuad1dldktkLhP4h1+kT9XHf3Wo6aCA9voG26uj6mV2N+ASuELdSw9HWZkL0x/9V/GVab0BJG2+HvOkXQz5w== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 | 24 ++++++++++++++++++++++ include/linux/huge_mm.h | 3 +++ mm/huge_memory.c | 7 +++++++ mm/khugepaged.c | 16 ++++++++++++--- 4 files changed, 47 insertions(+), 3 deletions(-) diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst index c51932e6275d..eebb1f6bbc6c 100644 --- a/Documentation/admin-guide/mm/transhuge.rst +++ b/Documentation/admin-guide/mm/transhuge.rst @@ -714,6 +714,30 @@ 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 collapse attempts that failed due to exceeding the + max_ptes_none threshold. For mTHP collapse, Currently only max_ptes_none + values of 0 and (HPAGE_PMD_NR - 1) are supported. Any other value will + emit a warning and no mTHP collapse will be attempted. khugepaged will + try to collapse to the largest enabled (m)THP size; if it fails, it will + try the next lower enabled mTHP size. This counter records the number of + times a collapse attempt was skipped for exceeding the max_ptes_none + threshold, and khugepaged will move on to the next available mTHP size. + +collapse_exceed_swap_pte + The number of anonymous mTHP PTE ranges which were unable to collapse due + to containing 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 were unable to collapse due + to containing 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 9941fc6d7bd8..e8777bb2347d 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 228f35e962b9..1049a207a257 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -642,6 +642,10 @@ 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, @@ -658,6 +662,9 @@ 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 c739f26dd61e..a6cf90e09e4a 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -595,7 +595,9 @@ static enum scan_result __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 (is_pmd_order(order)) + count_vm_event(THP_SCAN_EXCEED_NONE_PTE); + count_mthp_stat(order, MTHP_STAT_COLLAPSE_EXCEED_NONE); goto out; } } @@ -631,10 +633,17 @@ static enum scan_result __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 (!is_pmd_order(order) || (cc->is_khugepaged && - shared > khugepaged_max_ptes_shared)) { + if (!is_pmd_order(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; } } @@ -1081,6 +1090,7 @@ static enum scan_result __collapse_huge_page_swapin(struct mm_struct *mm, * range. */ if (!is_pmd_order(order)) { + count_mthp_stat(order, MTHP_STAT_COLLAPSE_EXCEED_SWAP); pte_unmap(pte); mmap_read_unlock(mm); result = SCAN_EXCEED_SWAP_PTE; -- 2.53.0