Re: [PATCH v2] mm: zswap: handle incorrect attempts to load of large folios

[Mika Penttilä]

On 6/8/24 05:36, Yosry Ahmed wrote:
> diff --git a/mm/zswap.c b/mm/zswap.c
> index b9b35ef86d9be..ebb878d3e7865 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1557,6 +1557,26 @@ bool zswap_load(struct folio *folio)
>  
>  	VM_WARN_ON_ONCE(!folio_test_locked(folio));
>  
> +	/*
> +	 * Large folios should not be swapped in while zswap is being used, as
> +	 * they are not properly handled. Zswap does not properly load large
> +	 * folios, and a large folio may only be partially in zswap.
> +	 *
> +	 * If any of the subpages are in zswap, reading from disk would result
> +	 * in data corruption, so return true without marking the folio uptodate
> +	 * so that an IO error is emitted (e.g. do_swap_page() will sigfault).
> +	 *
> +	 * Otherwise, return false and read the folio from disk.
> +	 */
> +	if (folio_test_large(folio)) {
> +		if (xa_find(tree, &offset,
> +			    offset + folio_nr_pages(folio) - 1, XA_PRESENT)) {
> +			WARN_ON_ONCE(1);
> +			return true;
> +		}

How does that work? Should it be xa_find_after() to not always find
current entry?

And does it still mean those subsequent entries map to same folio?


--Mika