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b=WAzRjjeS1kIAP0E5p16pH5QbLhJfbtxSYOlsW4z5lH6NyqDTB17LNvxRwmtF7Rp5lEVnOTtyugRvmCNJj57qLoCswGMM5Sh93BY4tZIrfFxMqnvm5vlmj2cXNpMvCxxN7A1ey/xa28F/GqWn5irkQgBZdSjxMqWyUX6/2YmNkuc= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from SA1PR12MB5672.namprd12.prod.outlook.com (2603:10b6:806:23c::5) by DM4PR12MB5963.namprd12.prod.outlook.com (2603:10b6:8:6a::8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8335.10; Fri, 10 Jan 2025 21:08:12 +0000 Received: from SA1PR12MB5672.namprd12.prod.outlook.com ([fe80::60f:5e8d:f0da:4eca]) by SA1PR12MB5672.namprd12.prod.outlook.com ([fe80::60f:5e8d:f0da:4eca%4]) with mapi id 15.20.8335.010; Fri, 10 Jan 2025 21:08:12 +0000 Message-ID: <7cf9f0fd-279e-4e4d-99ac-966a752090a2@amd.com> Date: Fri, 10 Jan 2025 15:08:08 -0600 User-Agent: Mozilla Thunderbird Reply-To: michael.day@amd.com Subject: Re: [RFC PATCH 2/2] KVM: guest_memfd: use filemap_grab_folios in write To: Nikita Kalyazin , willy@infradead.org, pbonzini@redhat.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: david@redhat.com, jthoughton@google.com, michael.roth@amd.com, ackerleytng@google.com, graf@amazon.de, jgowans@amazon.com, roypat@amazon.co.uk, derekmn@amazon.com, nsaenz@amazon.es, xmarcalx@amazon.com References: <20250110154659.95464-1-kalyazin@amazon.com> <20250110154659.95464-3-kalyazin@amazon.com> From: Mike Day Content-Language: en-US In-Reply-To: <20250110154659.95464-3-kalyazin@amazon.com> Content-Type: text/plain; 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This speeds up population by 8.3% due to the > reduction in locking and tree walking when adding folios to the > pagecache. > > Signed-off-by: Nikita Kalyazin > --- > virt/kvm/guest_memfd.c | 176 +++++++++++++++++++++++++++++++++-------- > 1 file changed, 143 insertions(+), 33 deletions(-) > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index e80566ef56e9..ccfadc3a7389 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -102,17 +102,134 @@ static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index) > return filemap_grab_folio(inode->i_mapping, index); > } > > +/* > + * Returns locked folios on success. The caller is responsible for > + * setting the up-to-date flag before the memory is mapped into the guest. > + * There is no backing storage for the memory, so the folios will remain > + * up-to-date until they're removed. > + * > + * Ignore accessed, referenced, and dirty flags. The memory is > + * unevictable and there is no storage to write back to. > + */ > +static int kvm_gmem_get_folios(struct inode *inode, pgoff_t index, > + struct folio **folios, int num) > +{ > + return filemap_grab_folios(inode->i_mapping, index, folios, num); > +} > + > #if defined(CONFIG_KVM_GENERIC_PRIVATE_MEM) && !defined(CONFIG_KVM_AMD_SEV) > +static int kvm_kmem_gmem_write_inner(struct inode *inode, pgoff_t index, > + const void __user *buf, > + struct folio **folios, int num) > +{ > + int ret, i, num_grabbed, num_written; > + > + num_grabbed = kvm_gmem_get_folios(inode, index, folios, num); > + if (num_grabbed < 0) > + return num_grabbed; > + > + for (i = 0; i < num_grabbed; i++) { > + struct folio *folio = folios[i]; > + void *vaddr; > + > + if (folio_test_hwpoison(folio)) { > + folio_unlock(folio); > + folio_put(folio); > + ret = -EFAULT; > + break; > + } > + > + if (folio_test_uptodate(folio)) { > + folio_unlock(folio); > + folio_put(folio); > + ret = -ENOSPC; > + break; > + } > + > + folio_unlock(folio); > + > + vaddr = kmap_local_folio(folio, 0); > + ret = copy_from_user(vaddr, buf + (i << PAGE_SHIFT), PAGE_SIZE); > + if (ret) > + ret = -EINVAL; > + kunmap_local(vaddr); > + > + if (ret) { > + folio_put(folio); > + break; > + } else { > + kvm_gmem_mark_prepared(folio); > + folio_put(folio); > + } > + } > + > + num_written = i; > + > + for (i = num_written; i < num_grabbed; i++) { > + folio_unlock(folios[i]); > + folio_put(folios[i]); > + } > + > + return num_written ?: ret; > +} > + > +static struct folio *kvm_kmem_gmem_write_folio(struct inode *inode, pgoff_t index, > + const char __user *buf) > This could probably be rewritten as: struct folio *p_folio; int ret; ret = kvm_kmem_gmem_write_inner(inode, index, buf, &p_folio, 1); if (ret == 1) return p_folio; else return ERR_PTR(ret); Would remove a few lines of duplicated code and use only one prototype. Mike +{ > + struct folio *folio; > + void *vaddr; > + int ret = 0; > + > + folio = kvm_gmem_get_folio(inode, index); > + if (IS_ERR(folio)) > + return ERR_PTR(-EFAULT); > + > + if (folio_test_hwpoison(folio)) { > + ret = -EFAULT; > + goto out_unlock_put; > + } > + > + if (folio_test_uptodate(folio)) { > + ret = -ENOSPC; > + goto out_unlock_put; > + } > + > + folio_unlock(folio); > + > + vaddr = kmap_local_folio(folio, 0); > + ret = copy_from_user(vaddr, buf, PAGE_SIZE); > + if (ret) > + ret = -EINVAL; > + kunmap_local(vaddr); > + > + if (ret) { > + folio_put(folio); > + kvm_gmem_mark_prepared(folio); > + goto out_err; > + } > + > + folio_put(folio); > + > + return folio; > + > +out_unlock_put: > + folio_unlock(folio); > + folio_put(folio); > +out_err: > + return ERR_PTR(ret); > +} > + > static ssize_t kvm_kmem_gmem_write(struct file *file, const char __user *buf, > size_t count, loff_t *offset) > { > + struct inode *inode = file_inode(file); > + int ret = 0, batch_size = FILEMAP_GET_FOLIOS_BATCH_SIZE; > pgoff_t start, end, index; > - ssize_t ret = 0; > > if (!PAGE_ALIGNED(*offset) || !PAGE_ALIGNED(count)) > return -EINVAL; > > - if (*offset + count > i_size_read(file_inode(file))) > + if (*offset + count > i_size_read(inode)) > return -EINVAL; > > if (!buf) > @@ -123,9 +240,8 @@ static ssize_t kvm_kmem_gmem_write(struct file *file, const char __user *buf, > > filemap_invalidate_lock(file->f_mapping); > > - for (index = start; index < end; ) { > - struct folio *folio; > - void *vaddr; > + for (index = start; index + batch_size - 1 < end; ) { > + struct folio *folios[FILEMAP_GET_FOLIOS_BATCH_SIZE] = { NULL }; > pgoff_t buf_offset = (index - start) << PAGE_SHIFT; > > if (signal_pending(current)) { > @@ -133,46 +249,40 @@ static ssize_t kvm_kmem_gmem_write(struct file *file, const char __user *buf, > goto out; > } > > - folio = kvm_gmem_get_folio(file_inode(file), index); > - if (IS_ERR(folio)) { > - ret = -EFAULT; > + ret = kvm_kmem_gmem_write_inner(inode, index, buf + buf_offset, folios, batch_size); > + if (ret < 0) > goto out; > - } > > - if (folio_test_hwpoison(folio)) { > - folio_unlock(folio); > - folio_put(folio); > - ret = -EFAULT; > + index += ret; > + if (ret < batch_size) > + break; > + } > + > + for (; index < end; index++) { > + struct folio *folio; > + pgoff_t buf_offset = (index - start) << PAGE_SHIFT; > + > + if (signal_pending(current)) { > + ret = -EINTR; > goto out; > } > > - if (folio_test_uptodate(folio)) { > - folio_unlock(folio); > - folio_put(folio); > - ret = -ENOSPC; > + folio = kvm_kmem_gmem_write_folio(inode, index, > + buf + buf_offset); > + if (IS_ERR(folio)) { > + ret = PTR_ERR(folio); > goto out; > } > - > - folio_unlock(folio); > - > - vaddr = kmap_local_folio(folio, 0); > - ret = copy_from_user(vaddr, buf + buf_offset, PAGE_SIZE); > - if (ret) > - ret = -EINVAL; > - kunmap_local(vaddr); > - > - kvm_gmem_mark_prepared(folio); > - folio_put(folio); > - > - index = folio_next_index(folio); > - *offset += PAGE_SIZE; > } > > out: > filemap_invalidate_unlock(file->f_mapping); > + if (index > start) { > + *offset += (index - start) << PAGE_SHIFT; > + return (index - start) << PAGE_SHIFT; > + } > > - return ret && start == (*offset >> PAGE_SHIFT) ? > - ret : *offset - (start << PAGE_SHIFT); > + return ret; > } > #endif >