On Thu, Apr 08, 2021 at 08:04:27PM +0800, Shiyang Ruan wrote: > 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...@fujitsu.com> > Reviewed-by: Christoph Hellwig <h...@lst.de> > Reviewed-by: Ritesh Harjani <rite...@linux.ibm.com> > --- > fs/dax.c | 39 ++++++++++++++++++++++++++++----------- > 1 file changed, 28 insertions(+), 11 deletions(-) > > diff --git a/fs/dax.c b/fs/dax.c > index b4fd3813457a..e6c1354b27a8 100644 > --- a/fs/dax.c > +++ b/fs/dax.c > @@ -722,6 +722,10 @@ static int copy_cow_page_dax(struct block_device *bdev, > struct dax_device *dax_d > return 0; > } > > +/* DAX Insert Flag for the entry we insert */
Might be worth mentioning that these are xarray marks for the inserted entry, since this comment didn't help much. > +#define DAX_IF_DIRTY (1 << 0) > +#define DAX_IF_COW (1 << 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 > @@ -729,16 +733,19 @@ static int copy_cow_page_dax(struct block_device *bdev, > struct dax_device *dax_d > * already in the tree, we will skip the insertion and just dirty the PMD as > * appropriate. > */ > -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) > +static void *dax_insert_entry(struct xa_state *xas, struct vm_fault *vmf, > + void *entry, pfn_t pfn, unsigned long flags, > + unsigned int insert_flags) Urk, two flags arguments. Oh, I see. We insert (shifted) pfn_t values into the mapping as xarray values, so @flags determines the state flags of the new entry value, whereas @insert_flags determines what xarray mark we're going to attach (if any) to the inserted value. --D > { > + struct address_space *mapping = vmf->vma->vm_file->f_mapping; > 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 +757,7 @@ 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 +781,9 @@ 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; > } > @@ -1109,8 +1119,7 @@ static vm_fault_t dax_load_hole(struct xa_state *xas, > pfn_t pfn = pfn_to_pfn_t(my_zero_pfn(vaddr)); > vm_fault_t ret; > > - *entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn, > - DAX_ZERO_PAGE, false); > + *entry = dax_insert_entry(xas, vmf, *entry, pfn, DAX_ZERO_PAGE, 0); > > ret = vmf_insert_mixed(vmf->vma, vaddr, pfn); > trace_dax_load_hole(inode, vmf, ret); > @@ -1137,8 +1146,8 @@ static vm_fault_t dax_pmd_load_hole(struct xa_state > *xas, struct vm_fault *vmf, > goto fallback; > > pfn = page_to_pfn_t(zero_page); > - *entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn, > - DAX_PMD | DAX_ZERO_PAGE, false); > + *entry = dax_insert_entry(xas, vmf, *entry, pfn, > + DAX_PMD | DAX_ZERO_PAGE, 0); > > if (arch_needs_pgtable_deposit()) { > pgtable = pte_alloc_one(vma->vm_mm); > @@ -1444,6 +1453,7 @@ static vm_fault_t dax_fault_actor(struct vm_fault *vmf, > pfn_t *pfnp, > bool write = vmf->flags & FAULT_FLAG_WRITE; > bool sync = dax_fault_is_synchronous(flags, vmf->vma, iomap); > unsigned long entry_flags = pmd ? DAX_PMD : 0; > + unsigned int insert_flags = 0; > int err = 0; > pfn_t pfn; > void *kaddr; > @@ -1466,8 +1476,15 @@ static vm_fault_t dax_fault_actor(struct vm_fault > *vmf, pfn_t *pfnp, > if (err) > return pmd ? VM_FAULT_FALLBACK : dax_fault_return(err); > > - *entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn, entry_flags, > - write && !sync); > + if (write) { > + if (!sync) > + insert_flags |= DAX_IF_DIRTY; > + if (iomap->flags & IOMAP_F_SHARED) > + insert_flags |= DAX_IF_COW; > + } > + > + *entry = dax_insert_entry(xas, vmf, *entry, pfn, entry_flags, > + insert_flags); > > if (write && > srcmap->addr != IOMAP_HOLE && srcmap->addr != iomap->addr) { > -- > 2.31.0 > > >