+ mm-introduce-a-pageflag-for-partially-mapped-folios-fix.patch added to mm-unstable branch

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

The patch titled
     Subject: mm-introduce-a-pageflag-for-partially-mapped-folios-fix
has been added to the -mm mm-unstable branch.  Its filename is
     mm-introduce-a-pageflag-for-partially-mapped-folios-fix.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-introduce-a-pageflag-for-partially-mapped-folios-fix.patch

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

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Usama Arif <usamaarif642@gmail.com>
Subject: mm-introduce-a-pageflag-for-partially-mapped-folios-fix
Date: Thu, 15 Aug 2024 16:25:09 +0100

don't clear partially mapped bit in hugeTLB folios and fix deferred split THP stats

Link: https://lkml.kernel.org/r/4acdf2b7-ed65-4087-9806-8f4a187b4eb5@gmail.com
Signed-off-by: Usama Arif <usamaarif642@gmail.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Alexander Zhu <alexlzhu@fb.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Cc: Huan Yang <link@vivo.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Shuang Zhai <zhais@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/page-flags.h |    1 +
 mm/huge_memory.c           |   14 ++++++++------
 mm/hugetlb.c               |    1 -
 mm/rmap.c                  |    2 +-
 4 files changed, 10 insertions(+), 8 deletions(-)

--- a/include/linux/page-flags.h~mm-introduce-a-pageflag-for-partially-mapped-folios-fix
+++ a/include/linux/page-flags.h
@@ -863,6 +863,7 @@ static inline void ClearPageCompound(str
 }
 FOLIO_FLAG(large_rmappable, FOLIO_SECOND_PAGE)
 FOLIO_FLAG(partially_mapped, FOLIO_SECOND_PAGE)
+FOLIO_TEST_SET_FLAG(partially_mapped, FOLIO_SECOND_PAGE)
 #else
 FOLIO_FLAG_FALSE(large_rmappable)
 FOLIO_FLAG_FALSE(partially_mapped)
--- a/mm/huge_memory.c~mm-introduce-a-pageflag-for-partially-mapped-folios-fix
+++ a/mm/huge_memory.c
@@ -3452,6 +3452,7 @@ void __folio_undo_large_rmappable(struct
 	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
 }
 
+/* partially_mapped=false won't clear PG_partially_mapped folio flag */
 void deferred_split_folio(struct folio *folio, bool partially_mapped)
 {
 	struct deferred_split *ds_queue = get_deferred_split_queue(folio);
@@ -3481,16 +3482,17 @@ void deferred_split_folio(struct folio *
 		return;
 
 	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
-	if (partially_mapped)
-		folio_set_partially_mapped(folio);
-	else
-		folio_clear_partially_mapped(folio);
-	if (list_empty(&folio->_deferred_list)) {
-		if (partially_mapped) {
+	if (partially_mapped) {
+		if (!folio_test_set_partially_mapped(folio)) {
 			if (folio_test_pmd_mappable(folio))
 				count_vm_event(THP_DEFERRED_SPLIT_PAGE);
 			count_mthp_stat(folio_order(folio), MTHP_STAT_SPLIT_DEFERRED);
 		}
+	} else {
+		/* partially mapped folios cannot become non-partially mapped */
+		VM_WARN_ON_FOLIO(folio_test_partially_mapped(folio), folio);
+	}
+	if (list_empty(&folio->_deferred_list)) {
 		list_add_tail(&folio->_deferred_list, &ds_queue->split_queue);
 		ds_queue->split_queue_len++;
 #ifdef CONFIG_MEMCG
--- a/mm/hugetlb.c~mm-introduce-a-pageflag-for-partially-mapped-folios-fix
+++ a/mm/hugetlb.c
@@ -1758,7 +1758,6 @@ static void __update_and_free_hugetlb_fo
 		free_gigantic_folio(folio, huge_page_order(h));
 	} else {
 		INIT_LIST_HEAD(&folio->_deferred_list);
-		folio_clear_partially_mapped(folio);
 		folio_put(folio);
 	}
 }
--- a/mm/rmap.c~mm-introduce-a-pageflag-for-partially-mapped-folios-fix
+++ a/mm/rmap.c
@@ -1578,7 +1578,7 @@ static __always_inline void __folio_remo
 	 * Check partially_mapped first to ensure it is a large folio.
 	 */
 	if (partially_mapped && folio_test_anon(folio) &&
-	    list_empty(&folio->_deferred_list))
+	    !folio_test_partially_mapped(folio))
 		deferred_split_folio(folio, true);
 
 	__folio_mod_stat(folio, -nr, -nr_pmdmapped);
_

Patches currently in -mm which might be from usamaarif642@gmail.com are

mm-free-zapped-tail-pages-when-splitting-isolated-thp-fix.patch
mm-introduce-a-pageflag-for-partially-mapped-folios.patch
mm-introduce-a-pageflag-for-partially-mapped-folios-fix.patch
mm-split-underutilized-thps.patch
mm-add-sysfs-entry-to-disable-splitting-underutilized-thps.patch