On Mon, Jan 26, 2026 at 12:53:01PM -0800, Eric Biggers wrote:
> Then for the final version in generic_readahead_merkle_tree(), one
> option would be:
>
> struct folio *folio;
>
> folio = __filemap_get_folio(inode->i_mapping, index, FGP_ACCESSED, 0);
> if (folio == ERR_PTR(-ENOENT) ||
> (!IS_ERR(folio) && !folio_test_uptodate(folio))) {
> DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);
>
> page_cache_ra_unbounded(&ractl, nr_pages, 0);
> }
> if (!IS_ERR(folio))
> folio_put(folio);
>
> Or as a diff from this series:
I ended up doing the second version (which is what I intended to do
anyway, but messed up the brace placement) in this patch. It then
automatically carries over to the readahead split.
>
> - if (PTR_ERR(folio) == -ENOENT ||
> - !(IS_ERR(folio) && !folio_test_uptodate(folio))) {
> + if (folio == ERR_PTR(-ENOENT) ||
> + (!IS_ERR(folio) && !folio_test_uptodate(folio))) {
>
> (Note that PTR_ERR() shouldn't be used before it's known that the
> pointer is an error pointer.)
That's new to me, and I can't find anything in the documentation or
implementation suggesting that. Your example code above also does
this as does plenty of code in the kernel elsewhere.
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