+ fsdaxxfs-set-the-shared-flag-when-file-extent-is-shared.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: fsdax,xfs: set the shared flag when file extent is shared
has been added to the -mm mm-unstable branch.  Its filename is
     fsdaxxfs-set-the-shared-flag-when-file-extent-is-shared.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fsdaxxfs-set-the-shared-flag-when-file-extent-is-shared.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Shiyang Ruan <ruansy.fnst@fujitsu.com>
Subject: fsdax,xfs: set the shared flag when file extent is shared
Date: Thu, 1 Dec 2022 15:28:54 +0000

If a dax page is shared, mapread at different offsets can also trigger
page fault on same dax page.  So, change the flag from "cow" to "shared". 
And get the shared flag from filesystem when read.

Link: https://lkml.kernel.org/r/1669908538-55-5-git-send-email-ruansy.fnst@fujitsu.com
Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/dax.c           |   19 +++++++------------
 fs/xfs/xfs_iomap.c |    2 +-
 2 files changed, 8 insertions(+), 13 deletions(-)

--- a/fs/dax.c~fsdaxxfs-set-the-shared-flag-when-file-extent-is-shared
+++ a/fs/dax.c
@@ -846,12 +846,6 @@ static bool dax_fault_is_synchronous(con
 		(iter->iomap.flags & IOMAP_F_DIRTY);
 }
 
-static bool dax_fault_is_cow(const struct iomap_iter *iter)
-{
-	return (iter->flags & IOMAP_WRITE) &&
-		(iter->iomap.flags & IOMAP_F_SHARED);
-}
-
 /*
  * By this point grab_mapping_entry() has ensured that we have a locked entry
  * of the appropriate size so we don't have to worry about downgrading PMDs to
@@ -865,13 +859,14 @@ static void *dax_insert_entry(struct xa_
 {
 	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
 	void *new_entry = dax_make_entry(pfn, flags);
-	bool dirty = !dax_fault_is_synchronous(iter, vmf->vma);
-	bool cow = dax_fault_is_cow(iter);
+	bool write = iter->flags & IOMAP_WRITE;
+	bool dirty = write && !dax_fault_is_synchronous(iter, vmf->vma);
+	bool shared = iter->iomap.flags & IOMAP_F_SHARED;
 
 	if (dirty)
 		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
 
-	if (cow || (dax_is_zero_entry(entry) && !(flags & DAX_ZERO_PAGE))) {
+	if (shared || (dax_is_zero_entry(entry) && !(flags & DAX_ZERO_PAGE))) {
 		unsigned long index = xas->xa_index;
 		/* we are replacing a zero page with block mapping */
 		if (dax_is_pmd_entry(entry))
@@ -883,12 +878,12 @@ static void *dax_insert_entry(struct xa_
 
 	xas_reset(xas);
 	xas_lock_irq(xas);
-	if (cow || dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
+	if (shared || dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
 		void *old;
 
 		dax_disassociate_entry(entry, mapping, false);
 		dax_associate_entry(new_entry, mapping, vmf->vma, vmf->address,
-				cow);
+				shared);
 		/*
 		 * Only swap our new entry into the page cache if the current
 		 * entry is a zero page or an empty entry.  If a normal PTE or
@@ -908,7 +903,7 @@ static void *dax_insert_entry(struct xa_
 	if (dirty)
 		xas_set_mark(xas, PAGECACHE_TAG_DIRTY);
 
-	if (cow)
+	if (write && shared)
 		xas_set_mark(xas, PAGECACHE_TAG_TOWRITE);
 
 	xas_unlock_irq(xas);
--- a/fs/xfs/xfs_iomap.c~fsdaxxfs-set-the-shared-flag-when-file-extent-is-shared
+++ a/fs/xfs/xfs_iomap.c
@@ -1215,7 +1215,7 @@ xfs_read_iomap_begin(
 		return error;
 	error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb, &imap,
 			       &nimaps, 0);
-	if (!error && (flags & IOMAP_REPORT))
+	if (!error && ((flags & IOMAP_REPORT) || IS_DAX(inode)))
 		error = xfs_reflink_trim_around_shared(ip, &imap, &shared);
 	xfs_iunlock(ip, lockmode);
 
_

Patches currently in -mm which might be from ruansy.fnst@fujitsu.com are

fsdax-introduce-page-share-for-fsdax-in-reflink-mode.patch
fsdax-invalidate-pages-when-cow.patch
fsdax-zero-the-edges-if-source-is-hole-or-unwritten.patch
fsdaxxfs-set-the-shared-flag-when-file-extent-is-shared.patch
fsdax-dedupe-iter-two-files-at-the-same-time.patch
xfs-use-dax-ops-for-zero-and-truncate-in-fsdax-mode.patch
fsdaxxfs-port-unshare-to-fsdax.patch
xfs-remove-restrictions-for-fsdax-and-reflink.patch