[RFC,29/37] fs: list file types that support speculative faults.

Commit Message

Michel Lespinasse April 7, 2021, 1:44 a.m. UTC

Add a speculative field to the vm_operations_struct, which indicates if
the associated file type supports speculative faults.

Initially this is set for files that implement fault() with filemap_fault().

Signed-off-by: Michel Lespinasse <[e-mail]>
---
 fs/btrfs/file.c    | 1 +
 fs/cifs/file.c     | 1 +
 fs/fuse/file.c     | 1 +
 fs/nfs/file.c      | 1 +
 fs/ubifs/file.c    | 1 +
 fs/vboxsf/file.c   | 1 +
 include/linux/mm.h | 7 +++++++
 mm/filemap.c       | 1 +
 8 files changed, 14 insertions(+)

Comments

Matthew Wilcox April 7, 2021, 2:39 a.m. UTC | #1

On Tue, Apr 06, 2021 at 06:44:54PM -0700, Michel Lespinasse wrote:
> Add a speculative field to the vm_operations_struct, which indicates if
> the associated file type supports speculative faults.
> 
> Initially this is set for files that implement fault() with filemap_fault().

Ugh, no.  This goes away if you don't call ->fault speculatively.

Patch

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 0e155f013839..b31851271e51 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2293,6 +2293,7 @@  static const struct vm_operations_struct btrfs_file_vm_ops = {
 	.fault		= filemap_fault,
 	.map_pages	= filemap_map_pages,
 	.page_mkwrite	= btrfs_page_mkwrite,
+	.speculative	= true,
 };
 
 static int btrfs_file_mmap(struct file	*filp, struct vm_area_struct *vma)
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 042e24aad410..a0d5fbb25c62 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -4116,6 +4116,7 @@  static const struct vm_operations_struct cifs_file_vm_ops = {
 	.fault = filemap_fault,
 	.map_pages = filemap_map_pages,
 	.page_mkwrite = cifs_page_mkwrite,
+	.speculative = true,
 };
 
 int cifs_file_strict_mmap(struct file *file, struct vm_area_struct *vma)
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 8cccecb55fb8..c4874240d157 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2354,6 +2354,7 @@  static const struct vm_operations_struct fuse_file_vm_ops = {
 	.fault		= filemap_fault,
 	.map_pages	= filemap_map_pages,
 	.page_mkwrite	= fuse_page_mkwrite,
+	.speculative	= true,
 };
 
 static int fuse_file_mmap(struct file *file, struct vm_area_struct *vma)
diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 16ad5050e046..e653c6bc23ca 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -588,6 +588,7 @@  static const struct vm_operations_struct nfs_file_vm_ops = {
 	.fault = filemap_fault,
 	.map_pages = filemap_map_pages,
 	.page_mkwrite = nfs_vm_page_mkwrite,
+	.speculative = true,
 };
 
 static int nfs_need_check_write(struct file *filp, struct inode *inode,
diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
index 0e4b4be3aa26..3d97f1c3e9c7 100644
--- a/fs/ubifs/file.c
+++ b/fs/ubifs/file.c
@@ -1598,6 +1598,7 @@  static const struct vm_operations_struct ubifs_file_vm_ops = {
 	.fault        = filemap_fault,
 	.map_pages = filemap_map_pages,
 	.page_mkwrite = ubifs_vm_page_mkwrite,
+	.speculative = true,
 };
 
 static int ubifs_file_mmap(struct file *file, struct vm_area_struct *vma)
diff --git a/fs/vboxsf/file.c b/fs/vboxsf/file.c
index c4ab5996d97a..e0a6a3af9cb9 100644
--- a/fs/vboxsf/file.c
+++ b/fs/vboxsf/file.c
@@ -146,6 +146,7 @@  static const struct vm_operations_struct vboxsf_file_vm_ops = {
 	.close		= vboxsf_vma_close,
 	.fault		= filemap_fault,
 	.map_pages	= filemap_map_pages,
+	.speculative	= true,
 };
 
 static int vboxsf_file_mmap(struct file *file, struct vm_area_struct *vma)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index f26490aff514..b4c0c10e434e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -641,6 +641,13 @@  struct vm_operations_struct {
 	 */
 	struct page *(*find_special_page)(struct vm_area_struct *vma,
 					  unsigned long addr);
+	/*
+	 * speculative indicates that the vm_operations support
+	 * speculative page faults. This allows ->fault and ->map_pages
+	 * to be called with FAULT_FLAG_SPECULATIVE set; such calls will
+	 * run within an rcu read locked section and with mmap lock not held.
+	 */
+	bool speculative;
 };
 
 static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm)
diff --git a/mm/filemap.c b/mm/filemap.c
index d496771749e6..b83040c672d3 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3226,6 +3226,7 @@  const struct vm_operations_struct generic_file_vm_ops = {
 	.fault		= filemap_fault,
 	.map_pages	= filemap_map_pages,
 	.page_mkwrite	= filemap_page_mkwrite,
+	.speculative	= true,
 };
 
 /* This is used for a general mmap of a disk file */