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Sun, 12 Apr 2026 18:38:50 -0700 (PDT) X-Received: by 2002:a05:690c:6987:b0:7b3:edc7:9b8f with SMTP id 00721157ae682-7b3edc7b61cmr1318877b3.0.1776044329838; Sun, 12 Apr 2026 18:38:49 -0700 (PDT) MIME-Version: 1.0 References: <20260226031741.230674-1-npache@redhat.com> <20260226032445.233437-1-npache@redhat.com> <94290ad5-f63d-4fa7-a898-dcfe6cd9998b@kernel.org> In-Reply-To: <94290ad5-f63d-4fa7-a898-dcfe6cd9998b@kernel.org> From: Nico Pache Date: Sun, 12 Apr 2026 19:38:41 -0600 X-Gm-Features: AQROBzArl5XlylTlxjRxCzhfJiWfRtUhtNUooNt0wkSwTm8sXKprqqkTO6ix5Ns Message-ID: Subject: Re: [PATCH mm-unstable v15 06/13] mm/khugepaged: skip collapsing mTHP to smaller orders To: "David Hildenbrand (Arm)" 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, 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, lorenzo.stoakes@oracle.com, 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 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: NzzAQFcgEDOuiQYQrfVjMA3vElS8en8XFEWHEA7oJc0_1776044330 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 0300A100002 X-Stat-Signature: zdhk45knu475a9sib5q4a4963anpnyz3 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1776044332-128279 X-HE-Meta: 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 FVPzeQII 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Mar 12, 2026 at 3:00=E2=80=AFPM David Hildenbrand (Arm) wrote: > > On 2/26/26 04:24, 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: Lorenzo Stoakes > > Reviewed-by: Baolin Wang > > Co-developed-by: Dev Jain > > Signed-off-by: Dev Jain > > Signed-off-by: Nico Pache > > --- > > mm/khugepaged.c | 8 ++++++++ > > 1 file changed, 8 insertions(+) > > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > index fb3ba8fe5a6c..c739f26dd61e 100644 > > --- a/mm/khugepaged.c > > +++ b/mm/khugepaged.c > > @@ -638,6 +638,14 @@ static enum scan_result __collapse_huge_page_isola= te(struct vm_area_struct *vma, > > goto out; > > } > > } > > + /* > > + * TODO: In some cases of partially-mapped folios, we'd a= ctually > > + * want to collapse. > > + */ > > + if (!is_pmd_order(order) && folio_order(folio) >=3D order= ) { > > + result =3D SCAN_PTE_MAPPED_HUGEPAGE; > > + goto out; > > + } > > > > if (folio_test_large(folio)) { > > struct folio *f; > > Why aren't we doing the same in hpage_collapse_scan_pmd() ? We can't do this in the scan phase because we are not yet aware of the order we want to collapse to. The scan phase builds the bitmap (if mthp sizes are enabled). I tried to think if there were any similar checks we could perform; the only one that came to mind is whether the current folio size exceeds the highest enabled folio size. Is that worth checking? Cheers, -- Nico > > -- > Cheers, > > David >