linux-ext4 - Re: [PATCH v4 10/12] dax: add struct iomap based DAX PMD support

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Date:   Fri, 30 Sep 2016 02:56:27 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.com>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-nvdimm@...1.01.org,
        linux-xfs@...r.kernel.org
Subject: Re: [PATCH v4 10/12] dax: add struct iomap based DAX PMD support

> -/*
> - * 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
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