From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 205D6332EC8; Mon, 27 Apr 2026 20:21:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777321289; cv=none; b=lYGOJ2S9c6uJISAJOrL7XGbV3xw9013I1uG/OD2U4kMS3mE9HLCIRqN3x31tapqQhnB4Na7KASMVQ/g18OQl6rR4mypSFQWvNk2+R2IkgYzWT2IfUob6i83dI9vw/5K8qci7VYmtQLoTiMh8ESFs/hoxvCra72dD6cWaATF8gWg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777321289; c=relaxed/simple; bh=LfEO2GoA4tssIBvxQvA9KN/YDpW25UUMbOSLYE27780=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Be/PQeLskA+trWBNziv0O5ht6ue9trsOhz+w302OzI7tZG9S9ohjJcF4hjRCn9vhN5gIIJyqFDkJij8pR/HPYHLGGow22Dm6HaGlBZcWLS7334E4Ckn4ZBykCDp5PB24bf5fAGqV66xmStAP59WCSCtEaUBB+bbxPo9g5SRN0go= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=scn2FMus; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="scn2FMus" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3ECBFC19425; Mon, 27 Apr 2026 20:21:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777321288; bh=LfEO2GoA4tssIBvxQvA9KN/YDpW25UUMbOSLYE27780=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; 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 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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