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Mon, 30 Oct 2023 10:24:49 -0700 (PDT) Message-ID: <601f24a0-cb55-458e-aa15-3970f2290172@redhat.com> Date: Mon, 30 Oct 2023 18:24:34 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v13 14/35] mm: Add AS_UNMOVABLE to mark mapping as completely unmovable To: Sean Christopherson , Marc Zyngier , Oliver Upton , Huacai Chen , Michael Ellerman , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexander Viro , Christian Brauner , "Matthew Wilcox (Oracle)" , Andrew Morton Cc: kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Xiaoyao Li , Xu Yilun , Chao Peng , Fuad Tabba , Jarkko Sakkinen , Anish Moorthy , David Matlack , Yu Zhang , Isaku Yamahata , =?UTF-8?B?TWlja2HDq2wgU2FsYcO8?= =?UTF-8?Q?n?= , Vlastimil Babka , Vishal Annapurve , Ackerley Tng , Maciej Szmigiero , David Hildenbrand , Quentin Perret , Michael Roth , Wang , Liam Merwick , Isaku Yamahata , "Kirill A . Shutemov" References: <20231027182217.3615211-1-seanjc@google.com> <20231027182217.3615211-15-seanjc@google.com> From: Paolo Bonzini Autocrypt: addr=pbonzini@redhat.com; keydata= xsEhBFRCcBIBDqDGsz4K0zZun3jh+U6Z9wNGLKQ0kSFyjN38gMqU1SfP+TUNQepFHb/Gc0E2 CxXPkIBTvYY+ZPkoTh5xF9oS1jqI8iRLzouzF8yXs3QjQIZ2SfuCxSVwlV65jotcjD2FTN04 hVopm9llFijNZpVIOGUTqzM4U55sdsCcZUluWM6x4HSOdw5F5Utxfp1wOjD/v92Lrax0hjiX DResHSt48q+8FrZzY+AUbkUS+Jm34qjswdrgsC5uxeVcLkBgWLmov2kMaMROT0YmFY6A3m1S P/kXmHDXxhe23gKb3dgwxUTpENDBGcfEzrzilWueOeUWiOcWuFOed/C3SyijBx3Av/lbCsHU Vx6pMycNTdzU1BuAroB+Y3mNEuW56Yd44jlInzG2UOwt9XjjdKkJZ1g0P9dwptwLEgTEd3Fo UdhAQyRXGYO8oROiuh+RZ1lXp6AQ4ZjoyH8WLfTLf5g1EKCTc4C1sy1vQSdzIRu3rBIjAvnC tGZADei1IExLqB3uzXKzZ1BZ+Z8hnt2og9hb7H0y8diYfEk2w3R7wEr+Ehk5NQsT2MPI2QBd wEv1/Aj1DgUHZAHzG1QN9S8wNWQ6K9DqHZTBnI1hUlkp22zCSHK/6FwUCuYp1zcAEQEAAc0j UGFvbG8gQm9uemluaSA8cGJvbnppbmlAcmVkaGF0LmNvbT7CwU0EEwECACMFAlRCcBICGwMH CwkIBwMCAQYVCAIJCgsEFgIDAQIeAQIXgAAKCRB+FRAMzTZpsbceDp9IIN6BIA0Ol7MoB15E 11kRz/ewzryFY54tQlMnd4xxfH8MTQ/mm9I482YoSwPMdcWFAKnUX6Yo30tbLiNB8hzaHeRj jx12K+ptqYbg+cevgOtbLAlL9kNgLLcsGqC2829jBCUTVeMSZDrzS97ole/YEez2qFpPnTV0 VrRWClWVfYh+JfzpXmgyhbkuwUxNFk421s4Ajp3d8nPPFUGgBG5HOxzkAm7xb1cjAuJ+oi/K CHfkuN+fLZl/u3E/fw7vvOESApLU5o0icVXeakfSz0LsygEnekDbxPnE5af/9FEkXJD5EoYG SEahaEtgNrR4qsyxyAGYgZlS70vkSSYJ+iT2rrwEiDlo31MzRo6Ba2FfHBSJ7lcYdPT7bbk9 AO3hlNMhNdUhoQv7M5HsnqZ6unvSHOKmReNaS9egAGdRN0/GPDWr9wroyJ65ZNQsHl9nXBqE AukZNr5oJO5vxrYiAuuTSd6UI/xFkjtkzltG3mw5ao2bBpk/V/YuePrJsnPFHG7NhizrxttB nTuOSCMo45pfHQ+XYd5K1+Cv/NzZFNWscm5htJ0HznY+oOsZvHTyGz3v91pn51dkRYN0otqr bQ4tlFFuVjArBZcapSIe6NV8C4cEiSTOwE0EVEJx7gEIAMeHcVzuv2bp9HlWDp6+RkZe+vtl KwAHplb/WH59j2wyG8V6i33+6MlSSJMOFnYUCCL77bucx9uImI5nX24PIlqT+zasVEEVGSRF m8dgkcJDB7Tps0IkNrUi4yof3B3shR+vMY3i3Ip0e41zKx0CvlAhMOo6otaHmcxr35sWq1Jk tLkbn3wG+fPQCVudJJECvVQ//UAthSSEklA50QtD2sBkmQ14ZryEyTHQ+E42K3j2IUmOLriF dNr9NvE1QGmGyIcbw2NIVEBOK/GWxkS5+dmxM2iD4Jdaf2nSn3jlHjEXoPwpMs0KZsgdU0pP JQzMUMwmB1wM8JxovFlPYrhNT9MAEQEAAcLBMwQYAQIACQUCVEJx7gIbDAAKCRB+FRAMzTZp sadRDqCctLmYICZu4GSnie4lKXl+HqlLanpVMOoFNnWs9oRP47MbE2wv8OaYh5pNR9VVgyhD OG0AU7oidG36OeUlrFDTfnPYYSF/mPCxHttosyt8O5kabxnIPv2URuAxDByz+iVbL+RjKaGM GDph56ZTswlx75nZVtIukqzLAQ5fa8OALSGum0cFi4ptZUOhDNz1onz61klD6z3MODi0sBZN Aj6guB2L/+2ZwElZEeRBERRd/uommlYuToAXfNRdUwrwl9gRMiA0WSyTb190zneRRDfpSK5d usXnM/O+kr3Dm+Ui+UioPf6wgbn3T0o6I5BhVhs4h4hWmIW7iNhPjX1iybXfmb1gAFfjtHfL xRUr64svXpyfJMScIQtBAm0ihWPltXkyITA92ngCmPdHa6M1hMh4RDX+Jf1fiWubzp1voAg0 JBrdmNZSQDz0iKmSrx8xkoXYfA3bgtFN8WJH2xgFL28XnqY4M6dLhJwV3z08tPSRqYFm4NMP dRsn0/7oymhneL8RthIvjDDQ5ktUjMe8LtHr70OZE/TT88qvEdhiIVUogHdo4qBrk41+gGQh b906Dudw5YhTJFU3nC6bbF2nrLlB4C/XSiH76ZvqzV0Z/cAMBo5NF/w= In-Reply-To: <20231027182217.3615211-15-seanjc@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 5A1EE10000C X-Stat-Signature: 43sjenmhpr9af5b5iaexa5jn1rqrhq1k X-HE-Tag: 1698686704-537170 X-HE-Meta: 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 EsMg3jwn 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/27/23 20:21, Sean Christopherson wrote: > Add an "unmovable" flag for mappings that cannot be migrated under any > circumstance. KVM will use the flag for its upcoming GUEST_MEMFD support, > which will not support compaction/migration, at least not in the > foreseeable future. > > Test AS_UNMOVABLE under folio lock as already done for the async > compaction/dirty folio case, as the mapping can be removed by truncation > while compaction is running. To avoid having to lock every folio with a > mapping, assume/require that unmovable mappings are also unevictable, and > have mapping_set_unmovable() also set AS_UNEVICTABLE. > > Cc: Matthew Wilcox > Co-developed-by: Vlastimil Babka > Signed-off-by: Vlastimil Babka > Signed-off-by: Sean Christopherson I think this could even be "From: Vlastimil", but no biggie. Paolo > --- > include/linux/pagemap.h | 19 +++++++++++++++++- > mm/compaction.c | 43 +++++++++++++++++++++++++++++------------ > mm/migrate.c | 2 ++ > 3 files changed, 51 insertions(+), 13 deletions(-) > > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h > index 351c3b7f93a1..82c9bf506b79 100644 > --- a/include/linux/pagemap.h > +++ b/include/linux/pagemap.h > @@ -203,7 +203,8 @@ enum mapping_flags { > /* writeback related tags are not used */ > AS_NO_WRITEBACK_TAGS = 5, > AS_LARGE_FOLIO_SUPPORT = 6, > - AS_RELEASE_ALWAYS, /* Call ->release_folio(), even if no private data */ > + AS_RELEASE_ALWAYS = 7, /* Call ->release_folio(), even if no private data */ > + AS_UNMOVABLE = 8, /* The mapping cannot be moved, ever */ > }; > > /** > @@ -289,6 +290,22 @@ static inline void mapping_clear_release_always(struct address_space *mapping) > clear_bit(AS_RELEASE_ALWAYS, &mapping->flags); > } > > +static inline void mapping_set_unmovable(struct address_space *mapping) > +{ > + /* > + * It's expected unmovable mappings are also unevictable. Compaction > + * migrate scanner (isolate_migratepages_block()) relies on this to > + * reduce page locking. > + */ > + set_bit(AS_UNEVICTABLE, &mapping->flags); > + set_bit(AS_UNMOVABLE, &mapping->flags); > +} > + > +static inline bool mapping_unmovable(struct address_space *mapping) > +{ > + return test_bit(AS_UNMOVABLE, &mapping->flags); > +} > + > static inline gfp_t mapping_gfp_mask(struct address_space * mapping) > { > return mapping->gfp_mask; > diff --git a/mm/compaction.c b/mm/compaction.c > index 38c8d216c6a3..12b828aed7c8 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -883,6 +883,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > > /* Time to isolate some pages for migration */ > for (; low_pfn < end_pfn; low_pfn++) { > + bool is_dirty, is_unevictable; > > if (skip_on_failure && low_pfn >= next_skip_pfn) { > /* > @@ -1080,8 +1081,10 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > if (!folio_test_lru(folio)) > goto isolate_fail_put; > > + is_unevictable = folio_test_unevictable(folio); > + > /* Compaction might skip unevictable pages but CMA takes them */ > - if (!(mode & ISOLATE_UNEVICTABLE) && folio_test_unevictable(folio)) > + if (!(mode & ISOLATE_UNEVICTABLE) && is_unevictable) > goto isolate_fail_put; > > /* > @@ -1093,26 +1096,42 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > if ((mode & ISOLATE_ASYNC_MIGRATE) && folio_test_writeback(folio)) > goto isolate_fail_put; > > - if ((mode & ISOLATE_ASYNC_MIGRATE) && folio_test_dirty(folio)) { > - bool migrate_dirty; > + is_dirty = folio_test_dirty(folio); > + > + if (((mode & ISOLATE_ASYNC_MIGRATE) && is_dirty) || > + (mapping && is_unevictable)) { > + bool migrate_dirty = true; > + bool is_unmovable; > > /* > * Only folios without mappings or that have > - * a ->migrate_folio callback are possible to > - * migrate without blocking. However, we may > - * be racing with truncation, which can free > - * the mapping. Truncation holds the folio lock > - * until after the folio is removed from the page > - * cache so holding it ourselves is sufficient. > + * a ->migrate_folio callback are possible to migrate > + * without blocking. > + * > + * Folios from unmovable mappings are not migratable. > + * > + * However, we can be racing with truncation, which can > + * free the mapping that we need to check. Truncation > + * holds the folio lock until after the folio is removed > + * from the page so holding it ourselves is sufficient. > + * > + * To avoid locking the folio just to check unmovable, > + * assume every unmovable folio is also unevictable, > + * which is a cheaper test. If our assumption goes > + * wrong, it's not a correctness bug, just potentially > + * wasted cycles. > */ > if (!folio_trylock(folio)) > goto isolate_fail_put; > > mapping = folio_mapping(folio); > - migrate_dirty = !mapping || > - mapping->a_ops->migrate_folio; > + if ((mode & ISOLATE_ASYNC_MIGRATE) && is_dirty) { > + migrate_dirty = !mapping || > + mapping->a_ops->migrate_folio; > + } > + is_unmovable = mapping && mapping_unmovable(mapping); > folio_unlock(folio); > - if (!migrate_dirty) > + if (!migrate_dirty || is_unmovable) > goto isolate_fail_put; > } > > diff --git a/mm/migrate.c b/mm/migrate.c > index 2053b54556ca..ed874e43ecd7 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -956,6 +956,8 @@ static int move_to_new_folio(struct folio *dst, struct folio *src, > > if (!mapping) > rc = migrate_folio(mapping, dst, src, mode); > + else if (mapping_unmovable(mapping)) > + rc = -EOPNOTSUPP; > else if (mapping->a_ops->migrate_folio) > /* > * Most folios have a mapping and most filesystems