11:13 p.m.
We replace the existing entry to the newly allocated one
in case of CoW. Also, we mark the entry as PAGECACHE_TAG_TOWRITE
so writeback marks this entry as writeprotected. This
helps us snapshots so new write pagefaults after snapshots
trigger a CoW.
Signed-off-by: Goldwyn Rodrigues <rgoldwyn(a)suse.com>
Signed-off-by: Shiyang Ruan <ruansy.fnst(a)cn.fujitsu.com>
---
fs/dax.c | 31 +++++++++++++++++++++++--------
1 file changed, 23 insertions(+), 8 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c
index 65553e3f7602..28b8e23b11ac 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -766,6 +766,9 @@ static int copy_user_dax(struct block_device *bdev, struct dax_device
*dax_dev,
return 0;
}
+#define DAX_IF_DIRTY (1ULL << 0)
+#define DAX_IF_COW (1ULL << 1)
+
/*
* 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
@@ -776,14 +779,16 @@ static int copy_user_dax(struct block_device *bdev, struct
dax_device *dax_dev,
static void *dax_insert_entry(struct xa_state *xas,
struct address_space *mapping, struct vm_fault *vmf,
pgoff_t bdoff, void *entry, pfn_t pfn, unsigned long flags,
- bool dirty)
+ bool insert_flags)
{
void *new_entry = dax_make_entry(pfn, flags);
+ bool dirty = insert_flags & DAX_IF_DIRTY;
+ bool cow = insert_flags & DAX_IF_COW;
if (dirty)
__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
- if (dax_is_zero_entry(entry) && !(flags & DAX_ZERO_PAGE)) {
+ if (cow || (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))
@@ -795,7 +800,7 @@ static void *dax_insert_entry(struct xa_state *xas,
xas_reset(xas);
xas_lock_irq(xas);
- if (dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
+ if (cow || dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
void *old;
dax_disassociate_entry(entry, mapping, false);
@@ -819,6 +824,9 @@ static void *dax_insert_entry(struct xa_state *xas,
if (dirty)
xas_set_mark(xas, PAGECACHE_TAG_DIRTY);
+ if (cow)
+ xas_set_mark(xas, PAGECACHE_TAG_TOWRITE);
+
xas_unlock_irq(xas);
return entry;
}
@@ -1366,6 +1374,7 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t
*pfnp,
void *entry;
pfn_t pfn;
void *kaddr;
+ unsigned long insert_flags = 0;
trace_dax_pte_fault(inode, vmf, ret);
/*
@@ -1491,8 +1500,10 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t
*pfnp,
goto finish_iomap;
case IOMAP_UNWRITTEN:
- if (write && iomap.flags & IOMAP_F_SHARED)
+ if (write && (iomap.flags & IOMAP_F_SHARED)) {
+ insert_flags |= DAX_IF_COW;
goto cow;
+ }
fallthrough;
case IOMAP_HOLE:
if (!write) {
@@ -1602,6 +1613,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t
*pfnp,
int error;
pfn_t pfn;
void *kaddr;
+ unsigned long insert_flags = 0;
/*
* Check whether offset isn't beyond end of file now. Caller is
@@ -1717,14 +1729,17 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t
*pfnp,
result = vmf_insert_pfn_pmd(vmf, pfn, write);
break;
case IOMAP_UNWRITTEN:
- if (write && iomap.flags & IOMAP_F_SHARED)
+ if (write && (iomap.flags & IOMAP_F_SHARED)) {
+ insert_flags |= DAX_IF_COW;
goto cow;
+ }
fallthrough;
case IOMAP_HOLE:
- if (WARN_ON_ONCE(write))
+ if (!write) {
+ result = dax_pmd_load_hole(&xas, vmf, &iomap, &entry);
break;
- result = dax_pmd_load_hole(&xas, vmf, &iomap, &entry);
- break;
+ }
+ fallthrough;
default:
WARN_ON_ONCE(1);
break;
--
2.27.0