Re: [PATCH 1/6] hugetlb: open-code hugetlb folio lookup index conversion

Matthew Wilcox
2026-04-20T18:27:30Z

On Thu, Apr 09, 2026 at 05:41:52PM -0600, Jane Chu wrote:
> This patch removes `filemap_lock_hugetlb_folio()` and open-codes
> the index conversion at each call site, making it explicit when
> hugetlb code is translating a hugepage index into the base-page index
> expected by `filemap_lock_folio()`

I think this is too large a piece to break off in a single patch.
The first thing I did was look at hugetlbfs_read_iter() and wonder
why we're not able to use generic_file_read_iter() here? It used
to be necessary because we used to index the page cache in units
of hsize, but now we don't, it seems to me that we could use
generic_file_read_iter() instead.

Now, what hugetlbfs_read_iter() does have is support for hwpoison
handling. I suspect this is something we want in
generic_file_read_iter(), it's just nobody's done it yet.

So perhaps that's patch 1 -- add hwpoison support to
generic_file_read_iter(). Then patch 2 removes hugetlbfs_read_iter() in
favour of using generic_file_read_iter().

Patch 3 is purely this:
(and you can put my Reviewed-by on it).

> @@ -652,10 +652,10 @@ static void hugetlbfs_zero_partial_page(struct hstate *h,
> loff_t start,
> loff_t end)
> {
> - pgoff_t idx = start >> huge_page_shift(h);
> + pgoff_t index = start >> PAGE_SHIFT;
> struct folio *folio;
>
> - folio = filemap_lock_hugetlb_folio(h, mapping, idx);
> + folio = filemap_lock_folio(mapping, index);
> if (IS_ERR(folio))
> return;
>

Now for patch 4 ...

> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index a786034ac95c..38b39eaf46cc 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5724,7 +5724,7 @@ static vm_fault_t hugetlb_no_page(struct address_space *mapping,
> * before we get page_table_lock.
> */
> new_folio = false;
> - folio = filemap_lock_hugetlb_folio(h, mapping, vmf->pgoff);
> + folio = filemap_lock_folio(mapping, vmf->pgoff << huge_page_order(h));
> if (IS_ERR(folio)) {
> size = i_size_read(mapping->host) >> huge_page_shift(h);
> if (vmf->pgoff >= size)

This points to a horrible problem. Everywhere else in the VM has
vmf->pgoff in PAGE_SIZE units, and of course hugetlb works in units of
hpagesize. So this is an entirely different piece of work where we
convert vmf->pgoff to be in units of PAGE_SIZE. That'll be fun!

> @@ -6208,7 +6208,7 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
>
> if (is_continue) {
> ret = -EFAULT;
> - folio = filemap_lock_hugetlb_folio(h, mapping, idx);
> + folio = filemap_lock_folio(mapping, idx << huge_page_order(h));
> if (IS_ERR(folio))
> goto out;
> folio_in_pagecache = true;

This is a much smaller (more contained) problem. At least idx is local
to this function, so you can calculate it using linear_page_index()
and modify the whole function.

Finally, you can delete filemap_lock_hugetlb_folio():

> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 9c098a02a09e..c64c6e5e50f5 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -829,12 +829,6 @@ static inline unsigned int blocks_per_huge_page(struct hstate *h)
> return huge_page_size(h) / 512;
> }
>
> -static inline struct folio *filemap_lock_hugetlb_folio(struct hstate *h,
> - struct address_space *mapping, pgoff_t idx)
> -{
> - return filemap_lock_folio(mapping, idx << huge_page_order(h));
> -}
> -
> #include <asm/hugetlb.h>
>
> #ifndef is_hugepage_only_range
> @@ -1106,12 +1100,6 @@ static inline struct hugepage_subpool *hugetlb_folio_subpool(struct folio *folio
> return NULL;
> }
>
> -static inline struct folio *filemap_lock_hugetlb_folio(struct hstate *h,
> - struct address_space *mapping, pgoff_t idx)
> -{
> - return NULL;
> -}
> -
> static inline int isolate_or_dissolve_huge_folio(struct folio *folio,
> struct list_head *list)
> {