+ mm-shmem-swap-tidy-up-thp-swapin-checks.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/shmem, swap: tidy up THP swapin checks
has been added to the -mm mm-unstable branch.  Its filename is
     mm-shmem-swap-tidy-up-thp-swapin-checks.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-shmem-swap-tidy-up-thp-swapin-checks.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Kairui Song <kasong@tencent.com>
Subject: mm/shmem, swap: tidy up THP swapin checks
Date: Sat, 5 Jul 2025 02:17:42 +0800

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/20250704181748.63181-4-ryncsn@gmail.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Reviewed-by: Baolin 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: Andrew Morton <akpm@linux-foundation.org>
---

 mm/shmem.c |   39 ++++++++++++++++++---------------------
 1 file changed, 18 insertions(+), 21 deletions(-)

--- a/mm/shmem.c~mm-shmem-swap-tidy-up-thp-swapin-checks
+++ a/mm/shmem.c
@@ -1980,26 +1980,38 @@ static struct folio *shmem_swap_alloc_fo
 		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);
@@ -2283,9 +2295,6 @@ static int shmem_swapin_folio(struct ino
 	/* 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;
@@ -2293,20 +2302,8 @@ static int shmem_swapin_folio(struct ino
 			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;
_

Patches currently in -mm which might be from kasong@tencent.com are

mm-list_lru-refactor-the-locking-code.patch
mm-shmem-swap-improve-cached-mthp-handling-and-fix-potential-hung.patch
mm-shmem-swap-avoid-redundant-xarray-lookup-during-swapin.patch
mm-shmem-swap-tidy-up-thp-swapin-checks.patch
mm-shmem-swap-tidy-up-swap-entry-splitting.patch
mm-shmem-swap-avoid-false-positive-swap-cache-lookup.patch
mm-shmem-swap-never-use-swap-cache-and-readahead-for-swp_synchronous_io.patch
mm-shmem-swap-simplify-swapin-path-and-result-handling.patch
mm-shmem-swap-simplify-swap-entry-and-index-calculation-of-large-swapin.patch
mm-shmem-swap-fix-major-fault-counting.patch