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Wed, 28 May 2025 11:02:52 +0000 Date: Wed, 28 May 2025 19:00:16 +0800 From: Yan Zhao To: Ackerley Tng CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [RFC PATCH v2 39/51] KVM: guest_memfd: Merge and truncate on fallocate(PUNCH_HOLE) Message-ID: Reply-To: Yan Zhao References: <625bd9c98ad4fd49d7df678f0186129226f77d7d.1747264138.git.ackerleytng@google.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <625bd9c98ad4fd49d7df678f0186129226f77d7d.1747264138.git.ackerleytng@google.com> X-ClientProxiedBy: SI2PR02CA0047.apcprd02.prod.outlook.com (2603:1096:4:196::14) To DS7PR11MB5966.namprd11.prod.outlook.com (2603:10b6:8:71::6) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS7PR11MB5966:EE_|SA3PR11MB8003:EE_ X-MS-Office365-Filtering-Correlation-Id: 207562ac-6671-4df0-f705-08dd9dd7312f X-LD-Processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|7416014|1800799024|376014|7053199007; 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> } > > +static long kvm_gmem_merge_truncate_indices(struct inode *inode, pgoff_t index, > + size_t nr_pages) > +{ > + struct folio *f; > + pgoff_t unused; > + long num_freed; > + > + unmap_mapping_pages(inode->i_mapping, index, nr_pages, false); > + > + if (!kvm_gmem_has_safe_refcount(inode->i_mapping, index, nr_pages, &unused)) Why is kvm_gmem_has_safe_refcount() checked here, but not in kvm_gmem_zero_range() within kvm_gmem_truncate_inode_range() in patch 33? > + return -EAGAIN; > + Rather than merging the folios, could we simply call kvm_gmem_truncate_indices() instead? num_freed = kvm_gmem_truncate_indices(inode->i_mapping, index, nr_pages); return num_freed; > + f = filemap_get_folio(inode->i_mapping, index); > + if (IS_ERR(f)) > + return 0; > + > + /* Leave just filemap's refcounts on the folio. */ > + folio_put(f); > + > + WARN_ON(kvm_gmem_merge_folio_in_filemap(inode, f)); > + > + num_freed = folio_nr_pages(f); > + folio_lock(f); > + truncate_inode_folio(inode->i_mapping, f); > + folio_unlock(f); > + > + return num_freed; > +} > + > #else > > static inline int kvm_gmem_try_split_folio_in_filemap(struct inode *inode, > @@ -874,6 +903,12 @@ static int kvm_gmem_restructure_folios_in_range(struct inode *inode, > return 0; > } > > +static long kvm_gmem_merge_truncate_indices(struct inode *inode, pgoff_t index, > + size_t nr_pages) > +{ > + return 0; > +} > + > #endif > > #else > @@ -1182,8 +1217,10 @@ static long kvm_gmem_truncate_indices(struct address_space *mapping, > * > * Removes folios beginning @index for @nr_pages from filemap in @inode, updates > * inode metadata. > + * > + * Return: 0 on success and negative error otherwise. > */ > -static void kvm_gmem_truncate_inode_aligned_pages(struct inode *inode, > +static long kvm_gmem_truncate_inode_aligned_pages(struct inode *inode, > pgoff_t index, > size_t nr_pages) > { > @@ -1191,19 +1228,34 @@ static void kvm_gmem_truncate_inode_aligned_pages(struct inode *inode, > long num_freed; > pgoff_t idx; > void *priv; > + long ret; > > priv = kvm_gmem_allocator_private(inode); > nr_per_huge_page = kvm_gmem_allocator_ops(inode)->nr_pages_in_folio(priv); > > + ret = 0; > num_freed = 0; > for (idx = index; idx < index + nr_pages; idx += nr_per_huge_page) { > - num_freed += kvm_gmem_truncate_indices( > - inode->i_mapping, idx, nr_per_huge_page); > + if (mapping_exiting(inode->i_mapping) || > + !kvm_gmem_has_some_shared(inode, idx, nr_per_huge_page)) { > + num_freed += kvm_gmem_truncate_indices( > + inode->i_mapping, idx, nr_per_huge_page); > + } else { > + ret = kvm_gmem_merge_truncate_indices(inode, idx, > + nr_per_huge_page); > + if (ret < 0) > + break; > + > + num_freed += ret; > + ret = 0; > + } > } > > spin_lock(&inode->i_lock); > inode->i_blocks -= (num_freed << PAGE_SHIFT) / 512; > spin_unlock(&inode->i_lock); > + > + return ret; > } > > /** > @@ -1252,8 +1304,10 @@ static void kvm_gmem_zero_range(struct address_space *mapping, > * > * Removes full (huge)pages from the filemap and zeroing incomplete > * (huge)pages. The pages in the range may be split. > + * > + * Return: 0 on success and negative error otherwise. > */ > -static void kvm_gmem_truncate_inode_range(struct inode *inode, loff_t lstart, > +static long kvm_gmem_truncate_inode_range(struct inode *inode, loff_t lstart, > loff_t lend) > { > pgoff_t full_hpage_start; > @@ -1263,6 +1317,7 @@ static void kvm_gmem_truncate_inode_range(struct inode *inode, loff_t lstart, > pgoff_t start; > pgoff_t end; > void *priv; > + long ret; > > priv = kvm_gmem_allocator_private(inode); > nr_per_huge_page = kvm_gmem_allocator_ops(inode)->nr_pages_in_folio(priv); > @@ -1279,10 +1334,11 @@ static void kvm_gmem_truncate_inode_range(struct inode *inode, loff_t lstart, > kvm_gmem_zero_range(inode->i_mapping, start, zero_end); > } > > + ret = 0; > if (full_hpage_end > full_hpage_start) { > nr_pages = full_hpage_end - full_hpage_start; > - kvm_gmem_truncate_inode_aligned_pages(inode, full_hpage_start, > - nr_pages); > + ret = kvm_gmem_truncate_inode_aligned_pages( > + inode, full_hpage_start, nr_pages); > } > > if (end > full_hpage_end && end > full_hpage_start) { > @@ -1290,6 +1346,8 @@ static void kvm_gmem_truncate_inode_range(struct inode *inode, loff_t lstart, > > kvm_gmem_zero_range(inode->i_mapping, zero_start, end); > } > + > + return ret; > } > > static long kvm_gmem_punch_hole(struct inode *inode, loff_t offset, loff_t len) > @@ -1298,6 +1356,7 @@ static long kvm_gmem_punch_hole(struct inode *inode, loff_t offset, loff_t len) > pgoff_t start = offset >> PAGE_SHIFT; > pgoff_t end = (offset + len) >> PAGE_SHIFT; > struct kvm_gmem *gmem; > + long ret; > > /* > * Bindings must be stable across invalidation to ensure the start+end > @@ -1308,8 +1367,9 @@ static long kvm_gmem_punch_hole(struct inode *inode, loff_t offset, loff_t len) > list_for_each_entry(gmem, gmem_list, entry) > kvm_gmem_invalidate_begin_and_zap(gmem, start, end); > > + ret = 0; > if (kvm_gmem_has_custom_allocator(inode)) { > - kvm_gmem_truncate_inode_range(inode, offset, offset + len); > + ret = kvm_gmem_truncate_inode_range(inode, offset, offset + len); > } else { > /* Page size is PAGE_SIZE, so use optimized truncation function. */ > truncate_inode_pages_range(inode->i_mapping, offset, offset + len - 1); > @@ -1320,7 +1380,7 @@ static long kvm_gmem_punch_hole(struct inode *inode, loff_t offset, loff_t len) > > filemap_invalidate_unlock(inode->i_mapping); > > - return 0; > + return ret; > } > > static long kvm_gmem_allocate(struct inode *inode, loff_t offset, loff_t len) > -- > 2.49.0.1045.g170613ef41-goog >