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Sun, 22 Feb 2026 23:04:50 -0800 (PST) Date: Mon, 23 Feb 2026 07:04:33 +0000 Mime-Version: 1.0 X-Mailer: git-send-email 2.53.0.345.g96ddfc5eaa-goog Message-ID: Subject: [RFC PATCH v1 00/10] guest_memfd: Track amount of memory allocated on inode From: Ackerley Tng To: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Cc: akpm@linux-foundation.org, david@kernel.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, willy@infradead.org, pbonzini@redhat.com, shuah@kernel.org, ackerleytng@google.com, seanjc@google.com, shivankg@amd.com, rick.p.edgecombe@intel.com, yan.y.zhao@intel.com, rientjes@google.com, fvdl@google.com, jthoughton@google.com, vannapurve@google.com, pratyush@kernel.org, pasha.tatashin@soleen.com, kalyazin@amazon.com, tabba@google.com, michael.roth@amd.com Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: D3816100009 X-Stat-Signature: 8ictyimyfjanxtkc6yt4yw5iok1hot7r X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1771830291-500313 X-HE-Meta: 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 HMLebGOx 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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: Hi, Currently, guest_memfd doesn't update inode's i_blocks or i_bytes at all. Hence, st_blocks in the struct populated by a userspace fstat() call on a guest_memfd will always be 0. This patch series makes guest_memfd track the amount of memory allocated on an inode, which allows fstat() to accurately report that on requests from userspace. The inode's i_blocks and i_bytes fields are updated when the folio is associated or disassociated from the guest_memfd inode, which are at allocation and truncation times respectively. To update inode fields at truncation time, this series implements a custom truncation function for guest_memfd. An alternative would be to update truncate_inode_pages_range() to return the number of bytes truncated or add/use some hook. Implementing a custom truncation function was chosen to provide flexibility for handling truncations in future when guest_memfd supports sources of pages other than the buddy allocator. This approach of a custom truncation function also aligns with shmem, which has a custom shmem_truncate_range(). To update inode fields at allocation time, kvm_gmem_get_folio() is simply augmented such that when a folio is added to the filemap, the size of the folio is updated into inode fields. The second patch, to use filemap_alloc_folio() during allocation of guest_memfd folios, was written as a debugging step to resolve a bug found by syzbot [1], but turned out to not be the fix. I include it here because it cleans up the allocation process and provides a nice foundation for updating inode fields during allocations. The first patch was separately submitted [2], and provided here since it is a prerequisite simplication before application of the second patch. [1] https://lore.kernel.org/all/29c347bde68ec027259654e8e85371307edf7058.1770148108.git.ackerleytng@google.com/ [2] https://lore.kernel.org/all/20260129172646.2361462-1-ackerleytng@google.com/ Ackerley Tng (10): KVM: guest_memfd: Don't set FGP_ACCESSED when getting folios KVM: guest_memfd: Directly allocate folios with filemap_alloc_folio() mm: truncate: Expose preparation steps for truncate_inode_pages_final() KVM: guest_memfd: Implement evict_inode for guest_memfd mm: Export unmap_mapping_folio() for KVM mm: filemap: Export filemap_remove_folio() KVM: guest_memfd: Implement custom truncation function KVM: guest_memfd: Track amount of memory allocated on inode KVM: selftests: Wrap fstat() to assert success KVM: selftests: Test that st_blocks is updated on allocation include/linux/mm.h | 3 + mm/filemap.c | 2 + mm/internal.h | 2 - mm/memory.c | 2 + mm/truncate.c | 21 +++- .../testing/selftests/kvm/guest_memfd_test.c | 32 +++-- .../selftests/kvm/include/kvm_syscalls.h | 2 + virt/kvm/guest_memfd.c | 116 +++++++++++++++--- 8 files changed, 149 insertions(+), 31 deletions(-) base-commit: b1195183ed42f1522fae3fe44ebee3af437aa000 -- 2.53.0.345.g96ddfc5eaa-goog