+ mm-huge_memory-move-memcg-switch-into-the-file-split-helper.patch added to mm-unstable branch

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

The patch titled
     Subject: mm/huge_memory: move memcg switch into the file split helper
has been added to the -mm mm-unstable branch.  Its filename is
     mm-huge_memory-move-memcg-switch-into-the-file-split-helper.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-huge_memory-move-memcg-switch-into-the-file-split-helper.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/huge_memory: move memcg switch into the file split helper
Date: Wed, 23 Sep 2026 23:32:44 +0200

The xarray node allocations in __folio_freeze_split_file() need to be
charged to the folio's memcg, so move the memcg switch from
__folio_split() into the helper.

The anon split helper and the after-split folio freeing perform no
chargeable allocations, so no memcg handling is left in __folio_split(). 
Rename its out_no_memcg label to out.

Link: https://lore.kernel.org/20260923-swap-thp-cleanup-v6-13-ba1b4ba72c6f@tencent.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Zi Yan <ziy@nvidia.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Reviewed-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Nico Pache <nico.pache@linux.dev>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Barry Song <baohua@kernel.org>
Cc: Youngjun Park <youngjun.park@lge.com>
Cc: Shivam Kalra <shivamkalra98@zohomail.in>
Cc: Kairui Song <ryncsn@gmail.com>
---

 mm/huge_memory.c |   36 +++++++++++++++++++-----------------
 1 file changed, 19 insertions(+), 17 deletions(-)

--- a/mm/huge_memory.c~mm-huge_memory-move-memcg-switch-into-the-file-split-helper
+++ a/mm/huge_memory.c
@@ -4142,6 +4142,7 @@ static int __folio_freeze_split_file(str
 	struct address_space *mapping = folio->mapping;
 	XA_STATE(xas, &mapping->i_pages, folio->index);
 	struct folio *end_folio = folio_next(folio);
+	struct mem_cgroup *memcg, *old_memcg;
 	struct folio *new_folio, *next;
 	int nr_shmem_dropped = 0;
 	unsigned int min_order;
@@ -4154,9 +4155,18 @@ static int __folio_freeze_split_file(str
 	if (new_order < min_order)
 		return -EINVAL;
 
+	/*
+	 * Switch to folio's memcg as xarray node allocation can happen and
+	 * needs to charge to it.
+	 */
+	memcg = get_mem_cgroup_from_folio(folio);
+	old_memcg = set_active_memcg(memcg);
+
 	gfp = current_gfp_context(mapping_gfp_mask(mapping) & GFP_RECLAIM_MASK);
-	if (!filemap_release_folio(folio, gfp))
-		return -EBUSY;
+	if (!filemap_release_folio(folio, gfp)) {
+		ret = -EBUSY;
+		goto fail_free;
+	}
 
 	mapping_set_update(&xas, mapping);
 
@@ -4288,6 +4298,9 @@ fail_mmap_unlock:
 	 */
 	i_mmap_unlock_read(mapping);
 fail_free:
+	/* Restore the previously active memcg */
+	set_active_memcg(old_memcg);
+	mem_cgroup_put(memcg);
 	xas_destroy(&xas);
 	return ret;
 }
@@ -4319,7 +4332,6 @@ static int __folio_split(struct folio *f
 {
 	struct folio *end_folio = folio_next(folio);
 	bool is_anon = folio_test_anon(folio);
-	struct mem_cgroup *memcg, *old_memcg;
 	int old_order = folio_order(folio);
 	struct folio *new_folio, *next;
 	int ret;
@@ -4329,27 +4341,20 @@ static int __folio_split(struct folio *f
 
 	if (folio != page_folio(split_at) || folio != page_folio(lock_at)) {
 		ret = -EINVAL;
-		goto out_no_memcg;
+		goto out;
 	}
 
 	if (new_order >= old_order) {
 		ret = -EINVAL;
-		goto out_no_memcg;
+		goto out;
 	}
 
 	ret = folio_check_splittable(folio, new_order, split_type);
 	if (ret) {
 		VM_WARN_ONCE(ret == -EINVAL, "Tried to split an unsplittable folio");
-		goto out_no_memcg;
+		goto out;
 	}
 
-	/*
-	 * switch to folio's memcg as xarray node allocation can happen and
-	 * needs to charge to it.
-	 */
-	memcg = get_mem_cgroup_from_folio(folio);
-	old_memcg = set_active_memcg(memcg);
-
 	if (is_anon)
 		ret = __folio_freeze_split_anon(folio, new_order, split_at,
 						true, list, split_type);
@@ -4376,10 +4381,7 @@ static int __folio_split(struct folio *f
 		free_folio_and_swap_cache(new_folio);
 	}
 
-	/* restore to caller's old_memcg */
-	set_active_memcg(old_memcg);
-	mem_cgroup_put(memcg);
-out_no_memcg:
+out:
 	if (is_pmd_order(old_order))
 		count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
 	count_mthp_stat(old_order, !ret ? MTHP_STAT_SPLIT : MTHP_STAT_SPLIT_FAILED);
_

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

mm-memcontrol-move-the-lru_zone_size-sanity-check-to-the-reader-side.patch
mm-mglru-introduce-helpers-for-manipulating-gen-and-refs-flags.patch
mm-migrate-copy-all-referenced-state-via-folio_migrate_lru_refs.patch
mm-mglru-move-max_seq-read-into-walk_update_folio.patch
mm-mglru-use-explicit-tier-range-in-read_ctrl_pos.patch
mm-mglru-fix-potential-generation-folio-number-leak.patch
mm-swap-fix-off-by-one-in-swap-cache-replace-sanity-check.patch
mm-huge_memory-fix-rejection-of-swap-cache-folios-with-a-mapping.patch
mm-huge_memory-invert-folio_ref_freeze-check-to-reduce-indentation.patch
mm-huge_memory-split-the-routine-for-splitting-anon-and-file-folio.patch
mm-huge_memory-rename-__split_unmapped_folio-to-__split_frozen_folio.patch
mm-huge_memory-consolidate-irq-and-locking-for-folio-split.patch
mm-huge_memory-move-eof-trimming-into-the-file-split-helper.patch
mm-huge_memory-move-unmap-and-remap-into-the-split-helpers.patch
mm-huge_memory-rename-remap_page-to-remap_anon_folio.patch
mm-huge_memory-move-the-racy-refcount-check-into-unmap_folio.patch
mm-huge_memory-move-filemap-management-into-the-file-split-helper.patch
mm-huge_memory-move-anon_vma-handling-into-the-anon-split-helper.patch
mm-huge_memory-move-memcg-switch-into-the-file-split-helper.patch
mm-huge_memory-drop-the-unused-do_lru-argument-of-the-file-split-helper.patch
mm-huge_memory-clean-up-after-split-folio-freeing-in-__folio_split.patch
mm-huge_memory-count-only-swap-cache-refs-in-anon-folio-split.patch
mm-huge_memory-drop-the-redundant-mapping-argument-of-__split_frozen_folio.patch