Re: [PATCH v14 00/74] Convert page cache to XArray

[Matthew Wilcox]

On Tue, Jun 19, 2018 at 10:16:38AM -0700, Matthew Wilcox wrote:
> I think I see a bug.  No idea if it's the one you're hitting ;-)
> 
> I had been intending to not use the 'entry' to decide whether we were
> waiting on a 2MB or 4kB page, but rather the xas.  I shelved that idea,
> but not before dropping the DAX_PMD flag being passed from the PMD
> pagefault caller.  So if I put that back ...

Did you get a chance to test this?

> diff --git a/fs/dax.c b/fs/dax.c
> index 9919b6b545fb..75cc160d2f0b 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -367,13 +367,13 @@ static struct page *dax_busy_page(void *entry)
>   * a VM_FAULT code, encoded as an xarray internal entry.  The ERR_PTR values
>   * overlap with xarray value entries.
>   */
> -static
> -void *grab_mapping_entry(struct xa_state *xas, struct address_space *mapping)
> +static void *grab_mapping_entry(struct xa_state *xas,
> +		struct address_space *mapping, unsigned long size)
>  {
>  	bool pmd_downgrade = false; /* splitting 2MiB entry into 4k entries? */
>  	void *locked = dax_make_entry(pfn_to_pfn_t(0),
> -						DAX_EMPTY | DAX_LOCKED);
> -	void *unlocked = dax_make_entry(pfn_to_pfn_t(0), DAX_EMPTY);
> +						size | DAX_EMPTY | DAX_LOCKED);
> +	void *unlocked = dax_make_entry(pfn_to_pfn_t(0), size | DAX_EMPTY);
>  	void *entry;
>  
>  retry:
> @@ -1163,7 +1163,7 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
>  	if (write && !vmf->cow_page)
>  		flags |= IOMAP_WRITE;
>  
> -	entry = grab_mapping_entry(&xas, mapping);
> +	entry = grab_mapping_entry(&xas, mapping, 0);
>  	if (xa_is_internal(entry)) {
>  		ret = xa_to_internal(entry);
>  		goto out;
> @@ -1396,7 +1396,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
>  	 * page is already in the tree, for instance), it will return
>  	 * VM_FAULT_FALLBACK.
>  	 */
> -	entry = grab_mapping_entry(&xas, mapping);
> +	entry = grab_mapping_entry(&xas, mapping, DAX_PMD);
>  	if (xa_is_internal(entry)) {
>  		result = xa_to_internal(entry);
>  		goto fallback;
>