On Fri, Mar 11, 2022 at 10:08:22AM +1100, Dave Chinner wrote:

On Thu, Mar 10, 2022 at 10:09:01PM +0800, Chao Peng wrote:

quoted

From: "Kirill A. Shutemov" <redacted>

It maintains a memfile_notifier list in shmem_inode_info structure and
implements memfile_pfn_ops callbacks defined by memfile_notifier. It
then exposes them to memfile_notifier via
shmem_get_memfile_notifier_info.

We use SGP_NOALLOC in shmem_get_lock_pfn since the pages should be
allocated by userspace for private memory. If there is no pages
allocated at the offset then error should be returned so KVM knows that
the memory is not private memory.

Signed-off-by: Kirill A. Shutemov <redacted>
Signed-off-by: Chao Peng <redacted>
---
 include/linux/shmem_fs.h |  4 +++
 mm/shmem.c               | 76 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 80 insertions(+)

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 2dde843f28ef..7bb16f2d2825 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h

@@ -9,6 +9,7 @@
 #include <linux/percpu_counter.h>
 #include <linux/xattr.h>
 #include <linux/fs_parser.h>
+#include <linux/memfile_notifier.h>
 
 /* inode in-kernel data */
 

@@ -28,6 +29,9 @@ struct shmem_inode_info {
 	struct simple_xattrs	xattrs;		/* list of xattrs */
 	atomic_t		stop_eviction;	/* hold when working on inode */
 	unsigned int		xflags;		/* shmem extended flags */
+#ifdef CONFIG_MEMFILE_NOTIFIER
+	struct memfile_notifier_list memfile_notifiers;
+#endif
 	struct inode		vfs_inode;
 };
 

diff --git a/mm/shmem.c b/mm/shmem.c
index 9b31a7056009..7b43e274c9a2 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c

@@ -903,6 +903,28 @@ static struct folio *shmem_get_partial_folio(struct inode *inode, pgoff_t index)
 	return page ? page_folio(page) : NULL;
 }
 
+static void notify_fallocate(struct inode *inode, pgoff_t start, pgoff_t end)
+{
+#ifdef CONFIG_MEMFILE_NOTIFIER
+	struct shmem_inode_info *info = SHMEM_I(inode);
+
+	memfile_notifier_fallocate(&info->memfile_notifiers, start, end);
+#endif
+}

*notify_populate(), not fallocate.  This is a notification that a
range has been populated, not that the fallocate() syscall was run
to populate the backing store of a file.

i.e.  fallocate is the name of a userspace filesystem API that can
be used to manipulate the backing store of a file in various ways.
It can both populate and punch away the backing store of a file, and
some operations that fallocate() can run will do both (e.g.
FALLOC_FL_ZERO_RANGE) and so could generate both
notify_invalidate() and a notify_populate() events.

Yes, I fully agreed fallocate syscall has both populating and hole
punching semantics so notify_fallocate can be misleading since we
actually mean populate here.

Hence "fallocate" as an internal mm namespace or operation does not
belong anywhere in core MM infrastructure - it should never get used
anywhere other than the VFS/filesystem layers that implement the
fallocate() syscall or use it directly.

Will use your suggestion through the series where applied. Thanks for
your suggestion.

Chao

Cheers,

Dave.

-- 
Dave Chinner
david@fromorbit.com