@@ -334,13 +334,46 @@ static unsigned long dax_end_pfn(void *entry)
for (pfn = dax_to_pfn(entry); \
pfn < dax_end_pfn(entry); pfn++)
+static inline void dax_mapping_set_cow_flag(struct address_space *mapping)
+{
+ mapping = (struct address_space *)PAGE_MAPPING_DAX_COW;
+}
+
+static inline bool dax_mapping_is_cow(struct address_space *mapping)
+{
+ return (unsigned long)mapping == PAGE_MAPPING_DAX_COW;
+}
+
/*
- * TODO: for reflink+dax we need a way to associate a single page with
- * multiple address_space instances at different linear_page_index()
- * offsets.
+ * Set or Update the page->mapping with FS_DAX_MAPPING_COW flag.
+ * Return true if it is an Update.
+ */
+static inline bool dax_mapping_set_cow(struct page *page)
+{
+ if (page->mapping) {
+ /* flag already set */
+ if (dax_mapping_is_cow(page->mapping))
+ return false;
+
+ /*
+ * This page has been mapped even before it is shared, just
+ * need to set this FS_DAX_MAPPING_COW flag.
+ */
+ dax_mapping_set_cow_flag(page->mapping);
+ return true;
+ }
+ /* Newly associate CoW mapping */
+ dax_mapping_set_cow_flag(page->mapping);
+ return false;
+}
+
+/*
+ * When it is called in dax_insert_entry(), the cow flag will indicate that
+ * whether this entry is shared by multiple files. If so, set the page->mapping
+ * to be FS_DAX_MAPPING_COW, and use page->index as refcount.
*/
static void dax_associate_entry(void *entry, struct address_space *mapping,
- struct vm_area_struct *vma, unsigned long address)
+ struct vm_area_struct *vma, unsigned long address, bool cow)
{
unsigned long size = dax_entry_size(entry), pfn, index;
int i = 0;
@@ -352,9 +385,17 @@ static void dax_associate_entry(void *entry, struct address_space *mapping,
for_each_mapped_pfn(entry, pfn) {
struct page *page = pfn_to_page(pfn);
- WARN_ON_ONCE(page->mapping);
- page->mapping = mapping;
- page->index = index + i++;
+ if (cow) {
+ if (dax_mapping_set_cow(page)) {
+ /* Was normal, now updated to CoW */
+ page->index = 2;
+ } else
+ page->index++;
+ } else {
+ WARN_ON_ONCE(page->mapping);
+ page->mapping = mapping;
+ page->index = index + i++;
+ }
}
}
@@ -370,7 +411,12 @@ static void dax_disassociate_entry(void *entry, struct address_space *mapping,
struct page *page = pfn_to_page(pfn);
WARN_ON_ONCE(trunc && page_ref_count(page) > 1);
- WARN_ON_ONCE(page->mapping && page->mapping != mapping);
+ if (!dax_mapping_is_cow(page->mapping)) {
+ /* keep the CoW flag if this page is still shared */
+ if (page->index-- > 0)
+ continue;
+ } else
+ WARN_ON_ONCE(page->mapping && page->mapping != mapping);
page->mapping = NULL;
page->index = 0;
}
@@ -829,7 +875,8 @@ static void *dax_insert_entry(struct xa_state *xas,
void *old;
dax_disassociate_entry(entry, mapping, false);
- dax_associate_entry(new_entry, mapping, vmf->vma, vmf->address);
+ dax_associate_entry(new_entry, mapping, vmf->vma, vmf->address,
+ false);
/*
* 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
@@ -572,6 +572,12 @@ __PAGEFLAG(Reported, reported, PF_NO_COMPOUND)
#define PAGE_MAPPING_KSM (PAGE_MAPPING_ANON | PAGE_MAPPING_MOVABLE)
#define PAGE_MAPPING_FLAGS (PAGE_MAPPING_ANON | PAGE_MAPPING_MOVABLE)
+/*
+ * Different with flags above, this flag is used only for fsdax mode. It
+ * indicates that this page->mapping is now under reflink case.
+ */
+#define PAGE_MAPPING_DAX_COW 0x1
+
static __always_inline int PageMappingFlags(struct page *page)
{
return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) != 0;
Introduce a PAGE_MAPPING_DAX_COW flag to support association with CoW file mappings. In this case, since the dax-rmap has already took the responsibility to look up for shared files by given dax page, the page->mapping is no longer to used for rmap but for marking that this dax page is shared. And to make sure disassociation works fine, we use page->index as refcount, and clear page->mapping to the initial state when page->index is decreased to 0. With the help of this new flag, it is able to distinguish normal case and CoW case, and keep the warning in normal case. == PS: The @cow added for dax_associate_entry(), is used to let it know whether the entry is to be shared during iomap operation. It is decided by iomap,srcmap's flag, and will be used in another patchset( fsdax,xfs: Add reflink&dedupe support for fsdax[1]). In this patch, we set @cow always false for now. [1] https://lore.kernel.org/linux-xfs/20210928062311.4012070-1-ruansy.fnst@fujitsu.com/ == Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com> --- fs/dax.c | 65 ++++++++++++++++++++++++++++++++------ include/linux/page-flags.h | 6 ++++ 2 files changed, 62 insertions(+), 9 deletions(-)