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[2003:d8:2f1d:ed00:1769:dd7c:7208:eb33]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b5e8e0d758sm17727799f8f.49.2025.07.16.07.32.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 16 Jul 2025 07:32:44 -0700 (PDT) Message-ID: <290d669f-e358-471a-95b7-c46f974742d0@redhat.com> Date: Wed, 16 Jul 2025 16:32:43 +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 v9 08/14] khugepaged: skip collapsing mTHP to smaller orders To: Nico Pache , linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, dev.jain@arm.com, corbet@lwn.net, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, akpm@linux-foundation.org, baohua@kernel.org, willy@infradead.org, peterx@redhat.com, wangkefeng.wang@huawei.com, usamaarif642@gmail.com, sunnanyong@huawei.com, vishal.moola@gmail.com, thomas.hellstrom@linux.intel.com, yang@os.amperecomputing.com, kirill.shutemov@linux.intel.com, aarcange@redhat.com, raquini@redhat.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, tiwai@suse.de, will@kernel.org, dave.hansen@linux.intel.com, jack@suse.cz, cl@gentwo.org, jglisse@google.com, surenb@google.com, zokeefe@google.com, hannes@cmpxchg.org, rientjes@google.com, mhocko@suse.com, rdunlap@infradead.org, hughd@google.com References: <20250714003207.113275-1-npache@redhat.com> <20250714003207.113275-9-npache@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 14.07.25 02:32, Nico Pache wrote: > khugepaged may try to collapse a mTHP to a smaller mTHP, resulting in > some pages being unmapped. Skip these cases until we have a way to check > if its ok to collapse to a smaller mTHP size (like in the case of a > partially mapped folio). > > This patch is inspired by Dev Jain's work on khugepaged mTHP support [1]. > > [1] https://lore.kernel.org/lkml/20241216165105.56185-11-dev.jain@arm.com/ > > Reviewed-by: Baolin Wang > Co-developed-by: Dev Jain > Signed-off-by: Dev Jain > Signed-off-by: Nico Pache > --- > mm/khugepaged.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 5d7c5be9097e..a701d9f0f158 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -612,7 +612,12 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, > folio = page_folio(page); > VM_BUG_ON_FOLIO(!folio_test_anon(folio), folio); > > - /* See hpage_collapse_scan_pmd(). */ > + if (order != HPAGE_PMD_ORDER && folio_order(folio) >= order) { > + result = SCAN_PTE_MAPPED_HUGEPAGE; > + goto out; > + } Probably worth adding a TODO in the code like /* * TODO: In some cases of partially-mapped folios, we'd actually * want to collapse. */ Acked-by: David Hildenbrand -- Cheers, David / dhildenb