+ kpageflags-detect-isolated-kpf_thp-folios.patch added to mm-unstable branch

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

The patch titled
     Subject: kpageflags: detect isolated KPF_THP folios
has been added to the -mm mm-unstable branch.  Its filename is
     kpageflags-detect-isolated-kpf_thp-folios.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kpageflags-detect-isolated-kpf_thp-folios.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: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Subject: kpageflags: detect isolated KPF_THP folios
Date: Fri, 5 Jul 2024 10:43:43 +0000

When folio is isolated, the PG_lru bit is cleared.  So the PG_lru check in
stable_page_flags() will miss this kind of isolated folios.  Use
folio_test_large_rmappable() instead to also include isolated folios.

Since pagecache supports large folios and the introduction of mTHP, the
semantics of KPF_THP have been expanded, now it indicates not only
PMD-sized THP.  Update related documentation to clearly state that KPF_THP
indicates multiple order THPs.

Link: https://lkml.kernel.org/r/20240705104343.112680-1-ranxiaokai627@163.com
Signed-off-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Andrei Vagin <avagin@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Svetly Todorov <svetly.todorov@memverge.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 Documentation/admin-guide/mm/pagemap.rst |    4 ++--
 fs/proc/page.c                           |   21 +++++++++------------
 2 files changed, 11 insertions(+), 14 deletions(-)

--- a/Documentation/admin-guide/mm/pagemap.rst~kpageflags-detect-isolated-kpf_thp-folios
+++ a/Documentation/admin-guide/mm/pagemap.rst
@@ -118,7 +118,7 @@ Short descriptions to the page flags
 21 - KSM
     Identical memory pages dynamically shared between one or more processes.
 22 - THP
-    Contiguous pages which construct transparent hugepages.
+    Contiguous pages which construct THP of any size and mapped by any granularity.
 23 - OFFLINE
     The page is logically offline.
 24 - ZERO_PAGE
@@ -231,7 +231,7 @@ Following flags about pages are currentl
 - ``PAGE_IS_PRESENT`` - Page is present in the memory
 - ``PAGE_IS_SWAPPED`` - Page is in swapped
 - ``PAGE_IS_PFNZERO`` - Page has zero PFN
-- ``PAGE_IS_HUGE`` - Page is THP or Hugetlb backed
+- ``PAGE_IS_HUGE`` - Page is PMD-mapped THP or Hugetlb backed
 - ``PAGE_IS_SOFT_DIRTY`` - Page is soft-dirty
 
 The ``struct pm_scan_arg`` is used as the argument of the IOCTL.
--- a/fs/proc/page.c~kpageflags-detect-isolated-kpf_thp-folios
+++ a/fs/proc/page.c
@@ -147,19 +147,16 @@ u64 stable_page_flags(const struct page
 		u |= 1 << KPF_COMPOUND_TAIL;
 	if (folio_test_hugetlb(folio))
 		u |= 1 << KPF_HUGE;
-	/*
-	 * We need to check PageLRU/PageAnon
-	 * to make sure a given page is a thp, not a non-huge compound page.
-	 */
-	else if (folio_test_large(folio)) {
-		if ((k & (1 << PG_lru)) || is_anon)
-			u |= 1 << KPF_THP;
-		else if (is_huge_zero_folio(folio)) {
-			u |= 1 << KPF_ZERO_PAGE;
-			u |= 1 << KPF_THP;
-		}
-	} else if (is_zero_pfn(page_to_pfn(page)))
+	else if (folio_test_large(folio) &&
+	         folio_test_large_rmappable(folio)) {
+		/* Note: we indicate any THPs here, not just PMD-sized ones */
+		u |= 1 << KPF_THP;
+	} else if (is_huge_zero_folio(folio)) {
+		u |= 1 << KPF_ZERO_PAGE;
+		u |= 1 << KPF_THP;
+	} else if (is_zero_pfn(page_to_pfn(page))) {
 		u |= 1 << KPF_ZERO_PAGE;
+	}
 
 	/*
 	 * Caveats on high order pages: PG_buddy and PG_slab will only be set
_

Patches currently in -mm which might be from ran.xiaokai@zte.com.cn are

kpageflags-detect-isolated-kpf_thp-folios.patch