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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 Subject: Re: [PATCH v10 07/13] khugepaged: skip collapsing mTHP to smaller orders Message-ID: References: <20250819134205.622806-1-npache@redhat.com> <20250819134205.622806-8-npache@redhat.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250819134205.622806-8-npache@redhat.com> X-ClientProxiedBy: MM0P280CA0014.SWEP280.PROD.OUTLOOK.COM (2603:10a6:190:a::23) To DM4PR10MB8218.namprd10.prod.outlook.com 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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 Tue, Aug 19, 2025 at 07:41:59AM -0600, 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/ > > Acked-by: David Hildenbrand > Reviewed-by: Baolin Wang > Co-developed-by: Dev Jain > Signed-off-by: Dev Jain > Signed-off-by: Nico Pache Other than comment below, LGTM so: Reviewed-by: Lorenzo Stoakes > --- > mm/khugepaged.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 1ad7e00d3fd6..6a4cf7e4a7cc 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -611,6 +611,15 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, > folio = page_folio(page); > VM_BUG_ON_FOLIO(!folio_test_anon(folio), folio); > > + /* > + * TODO: In some cases of partially-mapped folios, we'd actually > + * want to collapse. > + */ Not a fan of adding todo's in code, they have a habit of being left forever. I'd maybe put a more written out comment something similar to the commit message. > + if (order != HPAGE_PMD_ORDER && folio_order(folio) >= order) { > + result = SCAN_PTE_MAPPED_HUGEPAGE; > + goto out; > + } > + > /* See collapse_scan_pmd(). */ > if (folio_maybe_mapped_shared(folio)) { > ++shared; > -- > 2.50.1 >