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Sun, 22 Feb 2026 23:05:00 -0800 (PST) Date: Mon, 23 Feb 2026 07:04:40 +0000 In-Reply-To: Mime-Version: 1.0 References: X-Mailer: git-send-email 2.53.0.345.g96ddfc5eaa-goog Message-ID: <976ac2117ed9be6339e898cd80daed8f32b5044e.1771826352.git.ackerleytng@google.com> Subject: [RFC PATCH v1 07/10] KVM: guest_memfd: Implement custom truncation function 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-Server: rspam10 X-Rspamd-Queue-Id: 4904CA000D X-Stat-Signature: 1apb4w9dnexfa1i3ntwmmabc9jsjr3pe X-Rspam-User: X-HE-Tag: 1771830302-969063 X-HE-Meta: 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 PBWSboTh 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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: Implement custom truncation function for guest_memfd, and replace calls to truncate_inode_pages_range() with calls to this custom truncation function. The custom truncation function removes a lot of the generality supported by truncate_inode_pages_range() not required by guest_memfd, such as + sub-PAGE_SIZE truncations + Support for writeback In a later patch, guest_memfd use this custom truncation function to handle updating of i_blocks and i_bytes in the inode during truncation. Signed-off-by: Ackerley Tng --- virt/kvm/guest_memfd.c | 43 ++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 41 insertions(+), 2 deletions(-) diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 57dec458bfa77..e6c66ab7062b3 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -247,6 +247,45 @@ static void kvm_gmem_invalidate_end(struct inode *inode, pgoff_t start, __kvm_gmem_invalidate_end(f, start, end); } +static void kvm_gmem_truncate_folio(struct folio *folio) +{ + folio_lock(folio); + + if (folio_mapped(folio)) + unmap_mapping_folio(folio); + + /* + * guest_memfd doesn't need writeback, skip anything to do with + * writeback and just clear the dirty flag. + */ + folio_clear_dirty(folio); + filemap_remove_folio(folio); + + folio_unlock(folio); +} + +static void kvm_gmem_truncate_range(struct inode *inode, pgoff_t start, + size_t nr_pages) + +{ + struct folio_batch fbatch; + pgoff_t next; + pgoff_t last; + int i; + + last = start + nr_pages - 1; + + folio_batch_init(&fbatch); + next = start; + while (filemap_get_folios(inode->i_mapping, &next, last, &fbatch)) { + for (i = 0; i < folio_batch_count(&fbatch); ++i) + kvm_gmem_truncate_folio(fbatch.folios[i]); + + folio_batch_release(&fbatch); + cond_resched(); + } +} + static long kvm_gmem_punch_hole(struct inode *inode, loff_t offset, loff_t len) { pgoff_t start = offset >> PAGE_SHIFT; @@ -260,7 +299,7 @@ static long kvm_gmem_punch_hole(struct inode *inode, loff_t offset, loff_t len) kvm_gmem_invalidate_begin(inode, start, end); - truncate_inode_pages_range(inode->i_mapping, offset, offset + len - 1); + kvm_gmem_truncate_range(inode, offset, len >> PAGE_SHIFT); kvm_gmem_invalidate_end(inode, start, end); @@ -984,7 +1023,7 @@ static void kvm_gmem_evict_inode(struct inode *inode) truncate_inode_pages_final_prepare(mapping); - truncate_inode_pages_range(mapping, 0, inode->i_size); + kvm_gmem_truncate_range(inode, 0, inode->i_size >> PAGE_SHIFT); clear_inode(inode); } -- 2.53.0.345.g96ddfc5eaa-goog