Re: [PATCH 08/13] fs: add read support for RWF_UNCACHED

[Matthew Wilcox]

On Fri, Nov 08, 2024 at 10:43:31AM -0700, Jens Axboe wrote:
> +++ b/mm/swap.c
> @@ -472,6 +472,8 @@ static void folio_inc_refs(struct folio *folio)
>   */
>  void folio_mark_accessed(struct folio *folio)
>  {
> +	if (folio_test_uncached(folio))
> +		return;
>  	if (lru_gen_enabled()) {

This feels like it might be a problem.  If, eg, process A is doing
uncached IO and process B comes along and, say, mmap()s it, I think
we'll need to clear the uncached flag in order to have things work
correctly.  It's a performance problem, not a correctness problem.