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b=HGujj4tDkadqTA9Q8vNWga74uKYF9W9ayMskIVPbIn5pPH6oxITdEMT2GhUPh1k+n sqDs5jEwPtLZnq1QYz/22DN4VB5+zAWkYvZs30wRNPprt3r82UM/HuoWyfPpsye9kW b9D/JXZ5pztZrfUd2YLKeOWywci2An1XYFTmdO9kpksI3SMlbGT3ZeQpZU5+l6Y7ed 3ClUukjPJTkQJtxZ9N4hREXHZTTqGNQzeNlWJLr4+75uUDnwo1Rp3cBiTwm6n6S2EH 4Agp83sUSHwwN6a2Q1i8nFlUgKXAdZR+4l4N+/p0C6aWUDoUwfL8BvInhzGZG4wfka am9uNQNtvTgng== Date: Mon, 1 Jun 2026 15:13:28 +0100 From: Lorenzo Stoakes To: Nico Pache Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, 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@infradead.org, 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 Subject: Re: [PATCH mm-unstable v18 08/14] mm/khugepaged: add per-order mTHP collapse failure statistics Message-ID: References: <20260522150009.121603-1-npache@redhat.com> <20260522150009.121603-9-npache@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260522150009.121603-9-npache@redhat.com> X-Rspamd-Server: rspam11 X-Stat-Signature: p9yje4cpuig7tri83ftebbwb4cnf8mbj X-Rspamd-Queue-Id: 5B45D14001A X-Rspam-User: X-HE-Tag: 1780323224-87450 X-HE-Meta: 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 FeROv2rz tUHKlXS5hXotKBQ3A9gS92Bwo/Cy1tUok2qD11S/xhftmnwAzsqGQwzf259sLNCy5LV1bqGw+VOWftusl85/tBA4bzRBK0rmVYRAOEUclAanrZeu40gySGSLwjmmBpXMRHqffb/iUl/sT10aza3pPx14o7PHAIOHYcCBFCF5TEDBnn0Ir5W+LTxFB52D+SoA0W4b+JhW2Ws8TE0lGWwVaOefa1H5cn1Csp/TLPisIWXKHcuzuGPJnrzuDHpaDLYBDkO4e5G+J7RP7etCJUhDXFK9g6oxSOZwWrr29nJk3hBM0FyaOq6/pLLutzkLuT11Cin30fgUFB1Tqz8wn8hKKhYxjDQIy0ZGrp1EZ4SADo6jeM5A= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, May 22, 2026 at 09:00:03AM -0600, 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 > encountering a swap PTE. > > - 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 > encountering a shared PTE. > > 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 do not 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. > > We will add support for mTHP collapse for anonymous pages next; lets also > track when this happens at the PMD level within the per-mTHP stats. > > Signed-off-by: Nico Pache Logic LGTM, small comment below, but otherwise: Reviewed-by: Lorenzo Stoakes > --- > Documentation/admin-guide/mm/transhuge.rst | 14 ++++++++++++++ > include/linux/huge_mm.h | 3 +++ > mm/huge_memory.c | 7 +++++++ > mm/khugepaged.c | 21 +++++++++++++++++++-- > 4 files changed, 43 insertions(+), 2 deletions(-) > > diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst > index c51932e6275d..80a4d0bed70b 100644 > --- a/Documentation/admin-guide/mm/transhuge.rst > +++ b/Documentation/admin-guide/mm/transhuge.rst > @@ -714,6 +714,20 @@ 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. > + > +collapse_exceed_swap_pte > + The number of collapse attempts that failed due to exceeding the > + max_ptes_swap threshold. For non-PMD orders this occurs if a mTHP range > + contains at least one swap PTE. > + > +collapse_exceed_shared_pte > + The number of collapse attempts that failed due to exceeding the > + max_ptes_shared threshold. For non-PMD orders this occurs if a mTHP range > + contains at least one 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 ba7ae6808544..48496f09909b 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 345c54133c83..5c128cdec810 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -703,6 +703,10 @@ 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, > @@ -719,6 +723,9 @@ 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 928e32a0d4d7..fff6a8fbf1d4 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -649,7 +649,9 @@ static enum scan_result __collapse_huge_page_isolate(struct vm_area_struct *vma, > if (pte_none_or_zero(pteval)) { > if (++none_or_zero > max_ptes_none) { > 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; > } > continue; > @@ -683,9 +685,17 @@ static enum scan_result __collapse_huge_page_isolate(struct vm_area_struct *vma, > > /* See collapse_scan_pmd(). */ > if (folio_maybe_mapped_shared(folio)) { > + /* > + * TODO: Support shared pages without leading to further > + * mTHP collapses. Currently bringing in new pages via > + * shared may cause a future higher order collapse on a > + * rescan of the same range. > + */ Seems weird to add this comment in a stats update patch? Not a massively big deal but maybe worth moving to the relevant commit. > if (++shared > max_ptes_shared) { > result = SCAN_EXCEED_SHARED_PTE; > - count_vm_event(THP_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); > goto out; > } > } > @@ -1138,6 +1148,7 @@ 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; > @@ -1433,6 +1444,8 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, > if (++none_or_zero > max_ptes_none) { > result = SCAN_EXCEED_NONE_PTE; > count_vm_event(THP_SCAN_EXCEED_NONE_PTE); > + count_mthp_stat(HPAGE_PMD_ORDER, > + MTHP_STAT_COLLAPSE_EXCEED_NONE); > goto out_unmap; > } > continue; > @@ -1441,6 +1454,8 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, > if (++unmapped > max_ptes_swap) { > result = SCAN_EXCEED_SWAP_PTE; > count_vm_event(THP_SCAN_EXCEED_SWAP_PTE); > + count_mthp_stat(HPAGE_PMD_ORDER, > + MTHP_STAT_COLLAPSE_EXCEED_SWAP); > goto out_unmap; > } > /* > @@ -1498,6 +1513,8 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, > if (++shared > max_ptes_shared) { > result = SCAN_EXCEED_SHARED_PTE; > count_vm_event(THP_SCAN_EXCEED_SHARED_PTE); > + count_mthp_stat(HPAGE_PMD_ORDER, > + MTHP_STAT_COLLAPSE_EXCEED_SHARED); > goto out_unmap; > } > } > -- > 2.54.0 >