Re: [PATCH v4 10/12] dax: add struct iomap based DAX PMD support

Christoph Hellwig
2016-09-30T09:56:38Z

> -/*
> - * We use lowest available bit in exceptional entry for locking, other two
> - * bits to determine entry type. In total 3 special bits.
> - */
> -#define RADIX_DAX_SHIFT (RADIX_TREE_EXCEPTIONAL_SHIFT + 3)
> -#define RADIX_DAX_PTE (1 << (RADIX_TREE_EXCEPTIONAL_SHIFT + 1))
> -#define RADIX_DAX_PMD (1 << (RADIX_TREE_EXCEPTIONAL_SHIFT + 2))
> -#define RADIX_DAX_TYPE_MASK (RADIX_DAX_PTE | RADIX_DAX_PMD)
> -#define RADIX_DAX_TYPE(entry) ((unsigned long)entry & RADIX_DAX_TYPE_MASK)
> -#define RADIX_DAX_SECTOR(entry) (((unsigned long)entry >> RADIX_DAX_SHIFT))
> -#define RADIX_DAX_ENTRY(sector, pmd) ((void *)((unsigned long)sector << \
> - RADIX_DAX_SHIFT | (pmd ? RADIX_DAX_PMD : RADIX_DAX_PTE) | \
> - RADIX_TREE_EXCEPTIONAL_ENTRY))
> -

Please split the move of these constants into a separate patch.

> -static void *grab_mapping_entry(struct address_space *mapping, pgoff_t index)
> +static void *grab_mapping_entry(struct address_space *mapping, pgoff_t index,
> + unsigned long new_type)
> {
> + bool pmd_downgrade = false; /* splitting 2MiB entry into 4k entries? */
> void *entry, **slot;
>
> restart:
> spin_lock_irq(&mapping->tree_lock);
> entry = get_unlocked_mapping_entry(mapping, index, &slot);
> +
> + if (entry && new_type == RADIX_DAX_PMD) {
> + if (!radix_tree_exceptional_entry(entry) ||
> + RADIX_DAX_TYPE(entry) == RADIX_DAX_PTE) {
> + spin_unlock_irq(&mapping->tree_lock);
> + return ERR_PTR(-EEXIST);
> + }
> + } else if (entry && new_type == RADIX_DAX_PTE) {
> + if (radix_tree_exceptional_entry(entry) &&
> + RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD &&
> + (unsigned long)entry & (RADIX_DAX_HZP|RADIX_DAX_EMPTY)) {
> + pmd_downgrade = true;
> + }
> + }

Would be nice to use switch on the type here:

old_type = RADIX_DAX_TYPE(entry);

if (entry) {
switch (new_type) {
case RADIX_DAX_PMD:
if (!radix_tree_exceptional_entry(entry) ||
oldentry == RADIX_DAX_PTE) {
entry = ERR_PTR(-EEXIST);
goto out_unlock;
}
break;
case RADIX_DAX_PTE:
if (radix_tree_exceptional_entry(entry) &&
old_entry = RADIX_DAX_PMD &&
(unsigned long)entry &
(RADIX_DAX_HZP|RADIX_DAX_EMPTY))
..

Btw, why are only RADIX_DAX_PTE and RADIX_DAX_PMD in the type mask,
and not RADIX_DAX_HZP and RADIX_DAX_EMPTY? With that we could use the
above old_entry local variable over this function and make it a lot les
of a mess.

> static void *dax_insert_mapping_entry(struct address_space *mapping,
> struct vm_fault *vmf,
> - void *entry, sector_t sector)
> + void *entry, sector_t sector,
> + unsigned long new_type, bool hzp)

And then we could also drop the hzp argument here..

> #ifdef CONFIG_FS_IOMAP
> +static inline sector_t dax_iomap_sector(struct iomap *iomap, loff_t pos)
> +{
> + return iomap->blkno + (((pos & PAGE_MASK) - iomap->offset) >> 9);
> +}

Please split adding this new helper into a separate patch.

> +#if defined(CONFIG_FS_DAX_PMD)

Please use #ifdef here.

> +#define RADIX_DAX_TYPE(entry) ((unsigned long)entry & RADIX_DAX_TYPE_MASK)
> +#define RADIX_DAX_SECTOR(entry) (((unsigned long)entry >> RADIX_DAX_SHIFT))
> +
> +/* entries begin locked */
> +#define RADIX_DAX_ENTRY(sector, type) ((void *)(RADIX_TREE_EXCEPTIONAL_ENTRY |\
> + type | (unsigned long)sector << RADIX_DAX_SHIFT | RADIX_DAX_ENTRY_LOCK))
> +#define RADIX_DAX_HZP_ENTRY() ((void *)(RADIX_TREE_EXCEPTIONAL_ENTRY | \
> + RADIX_DAX_PMD | RADIX_DAX_HZP | RADIX_DAX_EMPTY | RADIX_DAX_ENTRY_LOCK))
> +#define RADIX_DAX_EMPTY_ENTRY(type) ((void *)(RADIX_TREE_EXCEPTIONAL_ENTRY | \
> + type | RADIX_DAX_EMPTY | RADIX_DAX_ENTRY_LOCK))
> +
> +#define RADIX_DAX_ORDER(type) (type == RADIX_DAX_PMD ? PMD_SHIFT-PAGE_SHIFT : 0)

All these macros don't properly brace their arguments. I think
you'd make your life a lot easier by making them inline functions.

> +#if defined(CONFIG_FS_DAX_PMD)

#ifdef, please