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Thu, 17 Jul 2025 00:25:26 -0700 (PDT) X-Google-Smtp-Source: AGHT+IE3zLwOVx14CX9ZFk5M7NptbR4Vtkv7y2swdOQcVV2bdsXyIwCQieST6so7r6GPy5LTDbi4OxzkmKDiHQeVo40= X-Received: by 2002:a05:690c:6c8f:b0:70a:2675:70b3 with SMTP id 00721157ae682-71837475aaemr81219087b3.17.1752737125474; Thu, 17 Jul 2025 00:25:25 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20250714003207.113275-1-npache@redhat.com> <20250714003207.113275-9-npache@redhat.com> <290d669f-e358-471a-95b7-c46f974742d0@redhat.com> In-Reply-To: <290d669f-e358-471a-95b7-c46f974742d0@redhat.com> From: Nico Pache Date: Thu, 17 Jul 2025 01:24:58 -0600 X-Gm-Features: Ac12FXw-dqZQr1iCc1PpyFCVkqA86TGy_82hTQcSrhEKTcjVPQocXibYjfgQIuE Message-ID: Subject: Re: [PATCH v9 08/14] khugepaged: skip collapsing mTHP to smaller orders To: David Hildenbrand Cc: linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, Jul 16, 2025 at 8:32=E2=80=AFAM David Hildenbrand wrote: > > 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 chec= k > > 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.c= om/ > > > > 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 =3D page_folio(page); > > VM_BUG_ON_FOLIO(!folio_test_anon(folio), folio); > > > > - /* See hpage_collapse_scan_pmd(). */ > > + if (order !=3D HPAGE_PMD_ORDER && folio_order(folio) >=3D= order) { > > + result =3D 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. > */ Done! Good idea with these TODOs! > > Acked-by: David Hildenbrand Thank you :) > > -- > Cheers, > > David / dhildenb >