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b=scn2FMus/b0JjqogLdL1wDKbOhtjb4L+4fyveZh+6uhBqW7Y0g/71/8fbdUzOr3SN QLG50KMOmamw+Y1/wXVXBqMm2LDSFWLU5TSDbwfgNlxpM/aZKD9rysUOEjIrftifAx F14WVFAnNNEEis874EELBsfe7CwrOLJDwFBNdUBN7LRz91k5xHPhn3za0ga5vYC/du NoOO6W1ZDCxyeII4mvcuOR6RFMenXxzNPetoA1GFxiqrAU7cEQ4s5doIZvEApqndOz eOsM3q6AFxWuMN0rIaoEouIjHCumxMVBhMbrAQ9xh1/qUkEZUyMhNgl7SJ8Eo7AgHp LnIkrFJ/wFRNw== Message-ID: Date: Mon, 27 Apr 2026 22:21:08 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 7.2 v16 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, ljs@kernel.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 References: <20260419185750.260784-1-npache@redhat.com> <20260419185750.260784-8-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-Server: rspam02 X-Rspamd-Queue-Id: EBC7840008 X-Rspam-User: X-Stat-Signature: unhksxgakcq4a5ekz8rzqjh1qhkduucg X-HE-Tag: 1777321289-351820 X-HE-Meta: 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 rY/ZfafD Krn04GuIoWQCb72C00iMZlcjJDnDexl/4nUFx/OJ458HorxjKQGiYKg41ykNieVJ1oOEHeKWcPlD0oTA2LfO+9OocWd00c15VN3qdAPAbJPReLPT6GEz/2n20somYPBln3kaqyu9FYJJX1bt80eFjdOGaXUPTfkh4cmxYNYFoaANDvcUM3nVirCcNxj8iExzRE5A4K47miLbORojwqanX/0JCJ2lIC1wk7n6PGsmmPjU/Jnq3ZGSuicNKSXos/t/B2WRn/kX4Z049BMYTYLKqG5Cb+6UVxMWKxyH0rZQVoKbAyWmfth9oT3okA27+m5nBQw+VOypJvnv+rgT1oQ0v/lc6AyXYNCivLkzu Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/19/26 20:57, 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 s/dont/do not/ > shared entry, those statistics keep track of how often we are > encountering failed mTHP collapses due to these restrictions. > > Now that we plan to support mTHP collapse for anon pages, lets also track "We will add support for mTHP collapse for anonymous pages next; let's also ..." > when this happens at the PMD level within the per-mTHP stats. What about file collapse? For example, we do adjust count_vm_event(THP_SCAN_EXCEED_SWAP_PTE) and count_vm_event(THP_SCAN_EXCEED_NONE_PTE) there. Wouldn't we want to update the HPAGE_PMD_ORDER side of things there already? or would we want to use a different counter for that? > > 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 | 21 +++++++++++++++++-- > 4 files changed, 53 insertions(+), 2 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. Why is everything after the first sentence worth documenting here? This doesn't read like it belongs to a failure counter? > + > +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. Can we similarly simplify that (and make it consistent with the one above) to "The number of collapse attempts that failed due to exceeding the max_ptes_swap threshold." > + > +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. Same here "The number of collapse attempts that failed due to exceeding the max_ptes_shared threshold." ? > + [...] -- Cheers, David