Commit c262ffd7 authored by Kairui Song's avatar Kairui Song Committed by Andrew Morton
Browse files

mm/shmem, swap: tidy up THP swapin checks 

Move all THP swapin related checks under CONFIG_TRANSPARENT_HUGEPAGE, so
they will be trimmed off by the compiler if not needed.

And add a WARN if shmem sees a order > 0 entry when
CONFIG_TRANSPARENT_HUGEPAGE is disabled, that should never happen unless
things went very wrong.

There should be no observable feature change except the new added WARN.

Link: https://lkml.kernel.org/r/20250728075306.12704-4-ryncsn@gmail.com


Signed-off-by: default avatarKairui Song <kasong@tencent.com>
Reviewed-by: default avatarBaolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 0cfc0e7e

mm/shmem.c

+18 −21
Original line number Diff line number Diff line
@@ -2017,26 +2017,38 @@ static struct folio *shmem_swap_alloc_folio(struct inode *inode, 
		swp_entry_t entry, int order, gfp_t gfp)

{

	struct shmem_inode_info *info = SHMEM_I(inode);

	int nr_pages = 1 << order;

	struct folio *new;

	void *shadow;

	int nr_pages;



	/*

	 * We have arrived here because our zones are constrained, so don't

	 * limit chance of success with further cpuset and node constraints.

	 */

	gfp &= ~GFP_CONSTRAINT_MASK;

	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && order > 0) {

		gfp_t huge_gfp = vma_thp_gfp_mask(vma);

	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {

		if (WARN_ON_ONCE(order))

			return ERR_PTR(-EINVAL);

	} else if (order) {

		/*

		 * If uffd is active for the vma, we need per-page fault

		 * fidelity to maintain the uffd semantics, then fallback

		 * to swapin order-0 folio, as well as for zswap case.

		 * Any existing sub folio in the swap cache also blocks

		 * mTHP swapin.

		 */

		if ((vma && unlikely(userfaultfd_armed(vma))) ||

		     !zswap_never_enabled() ||

		     non_swapcache_batch(entry, nr_pages) != nr_pages)

			return ERR_PTR(-EINVAL);



		gfp = limit_gfp_mask(huge_gfp, gfp);

		gfp = limit_gfp_mask(vma_thp_gfp_mask(vma), gfp);

	}



	new = shmem_alloc_folio(gfp, order, info, index);

	if (!new)

		return ERR_PTR(-ENOMEM);



	nr_pages = folio_nr_pages(new);

	if (mem_cgroup_swapin_charge_folio(new, vma ? vma->vm_mm : NULL,

					   gfp, entry)) {

		folio_put(new);
@@ -2320,9 +2332,6 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, 
	/* Look it up and read it in.. */

	folio = swap_cache_get_folio(swap, NULL, 0);

	if (!folio) {

		int nr_pages = 1 << order;

		bool fallback_order0 = false;



		/* Or update major stats only when swapin succeeds?? */

		if (fault_type) {

			*fault_type |= VM_FAULT_MAJOR;
@@ -2330,20 +2339,8 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, 
			count_memcg_event_mm(fault_mm, PGMAJFAULT);

		}



		/*

		 * If uffd is active for the vma, we need per-page fault

		 * fidelity to maintain the uffd semantics, then fallback

		 * to swapin order-0 folio, as well as for zswap case.

		 * Any existing sub folio in the swap cache also blocks

		 * mTHP swapin.

		 */

		if (order > 0 && ((vma && unlikely(userfaultfd_armed(vma))) ||

				  !zswap_never_enabled() ||

				  non_swapcache_batch(swap, nr_pages) != nr_pages))

			fallback_order0 = true;



		/* Skip swapcache for synchronous device. */

		if (!fallback_order0 && data_race(si->flags & SWP_SYNCHRONOUS_IO)) {

		if (data_race(si->flags & SWP_SYNCHRONOUS_IO)) {

			folio = shmem_swap_alloc_folio(inode, vma, index, swap, order, gfp);

			if (!IS_ERR(folio)) {

				skip_swapcache = true;