Re: [PATCH v2 04/11] mm, swap: add support for stable large allocation in swap cache directly

[Kairui Song]

On Fri, Apr 17, 2026 at 2:38 AM Kairui Song via B4 Relay
<devnull+kasong.tencent.com@xxxxxxxxxx> wrote:
> +/*
> + * Try to allocate a folio of given order in the swap cache.
> + *
> + * This helper resolves the potential races of swap allocation
> + * and prepares a folio to be used for swap IO. May return following
> + * value:
> + *
> + * -ENOMEM / -EBUSY: Order is too large or in conflict with sub slot,
> + *                   caller should shrink the order and retry.
> + * -ENOENT / -EEXIST: Target swap entry is unavailable or already cached,
> + *                    caller should abort or try use that folio instead.
> + */
> +static struct folio *__swap_cache_alloc(struct swap_cluster_info *ci,
> +                                       swp_entry_t targ_entry, gfp_t gfp,
> +                                       unsigned int order, struct vm_fault *vmf,
> +                                       struct mempolicy *mpol, pgoff_t ilx)
> +{
> +       int err;
> +       swp_entry_t entry;
> +       struct folio *folio;
> +       void *shadow = NULL;
> +       unsigned long address, nr_pages = 1 << order;
> +       struct vm_area_struct *vma = vmf ? vmf->vma : NULL;
> +
> +       entry.val = round_down(targ_entry.val, nr_pages);
> +
> +       /* Check if the slot and range are available, skip allocation if not */
> +       spin_lock(&ci->lock);
> +       err = __swap_cache_add_check(ci, targ_entry, nr_pages, NULL);
> +       spin_unlock(&ci->lock);
> +       if (unlikely(err))
> +               return ERR_PTR(err);
> +
> +       /*
> +        * Limit THP gfp. The limitation is a no-op for typical
> +        * GFP_HIGHUSER_MOVABLE but matters for shmem.
> +        */
> +       if (order)
> +               gfp = thp_limit_gfp_mask(vma_thp_gfp_mask(vma), gfp);
> +
> +       if (mpol) {
> +               folio = folio_alloc_mpol(gfp, order, mpol, ilx, numa_node_id());
> +       } else if (vmf) {
> +               address = round_down(vmf->address, PAGE_SIZE << order);
> +               folio = vma_alloc_folio(gfp, order, vmf->vma, address);
> +       } else {
> +               WARN_ON_ONCE(1);
> +               return ERR_PTR(-EINVAL);
> +       }

Checking sashiko's review, most are false positives but this part need
an update indeed, this part should be:

if (mpol || !vmf) {
        folio = folio_alloc_mpol(gfp, order, mpol, ilx, numa_node_id());
} else {
        address = round_down(vmf->address, PAGE_SIZE << order);
        folio = vma_alloc_folio(gfp, order, vmf->vma, address);
}