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 <rgold...@suse.com> Signed-off-by: Shiyang Ruan <ruansy.f...@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 b2195cbdf2dc..29698a3d2e37 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -722,6 +722,9 @@ static int copy_cow_page_dax(struct block_device *bdev, struct dax_device *dax_d 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 @@ -731,14 +734,16 @@ static int copy_cow_page_dax(struct block_device *bdev, struct dax_device *dax_d */ static void *dax_insert_entry(struct xa_state *xas, struct address_space *mapping, struct vm_fault *vmf, - void *entry, pfn_t pfn, unsigned long flags, bool dirty) + void *entry, pfn_t pfn, unsigned long flags, 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)) @@ -750,7 +755,7 @@ 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); @@ -774,6 +779,9 @@ 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; } @@ -1319,6 +1327,7 @@ 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); /* @@ -1444,8 +1453,10 @@ 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) { @@ -1555,6 +1566,7 @@ 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 @@ -1670,14 +1682,17 @@ 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; -- 2.30.0