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b=ougADOEQUaC5Qw7JSDoIRTSR3iRdA62MZrPNp0p4ZNCoGjRn758QQprGJbok31CxP 8YYIoffOLiWwOKlezeT/5ikXhTpapW4NjppnXTSCxqhLNSfJFfehX7iMXNTTq/fBQ5 X1lS4QfqH50c2JI8Nkn9zpyATVeoa0g9tjRC6HHyLbFX/i66rQsIOA5eeWISKm3Aw6 6FX/LSax1ODBp4DIC4yxQLQcwH41gr/vFR9c/qrPsPvyCiLgq9LmBgC0W1QFDaffy0 bz3PsJgaapTbI4Q+r+MaGKFl2UDeUcAY36Ppgmlzw344HG6E2rbwH1HfNEJPthptXk eQNTkFJ0zyC6Q== Message-ID: <01d1a79c-236f-4968-817f-d89c039019b0@kernel.org> Date: Thu, 12 Mar 2026 22:03:15 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-unstable v15 07/13] mm/khugepaged: add per-order mTHP collapse failure statistics To: Nico Pache , 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, 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, 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 References: <20260226031741.230674-1-npache@redhat.com> <20260226032504.233594-1-npache@redhat.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 8C81140006 X-Rspamd-Server: rspam07 X-Stat-Signature: mmag5uqkxkcwpdjgtutjmtz6odqhp8g4 X-Rspam-User: X-HE-Tag: 1773349415-938866 X-HE-Meta: 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 B3ttRQaT nN2XiMYVLnWtM8i9SQKCoUXKRMxI51vYGZhlB6zpjNO51KFv0Swi3mw1K3LIoT6GG9LGqQroEe+Uzl2gOL6xJajsPQswG3PVidUs5tSxUIB4txwIYI29R+gqAydrb5geGcKMBtRUJXKgYSajokaFh9/0Nbr1oc1c6ZR3zmRImraK4jXNE/mM8WLrnbS3hZMyWURZIHhAYkn2N3H8KGuOWiQsHFnthN6d4Vj1b/7uLJsaNGHgYEUV0B/dqaDQQS+L5tGEYhBPhyKkQKhjkg4faz3wup/cZeQlNz0GNKWJ2XF5LDSlGm6p+NDBd732F39h+7NkOU7l+p+qwDgh/WhSVosLf8q1Tps8yijGsw+CMtBxWmJUmHRA5+Qf5bQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/26/26 04:25, Nico Pache wrote: > 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; With the suggested earlier rework, this should hopefully become simply if (++shared > max_ptes_shared) { result = SCAN_EXCEED_SHARED_PTE; if (is_pmd_order(order)) count_vm_event(THP_SCAN_EXCEED_SHARED_PTE); count_mthp_stat(order, MTHP_STAT_COLLAPSE_EXCEED_SHARED); } With that (no code duplication) LGTM. -- Cheers, David