+ mm-replace-pf_kcompactd-flag-with-kthread_func-check.patch added to mm-new branch

+ mm-replace-pf_kcompactd-flag-with-kthread_func-check.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm: replace PF_KCOMPACTD flag with kthread_func() check
has been added to the -mm mm-new branch.  Its filename is
     mm-replace-pf_kcompactd-flag-with-kthread_func-check.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-replace-pf_kcompactd-flag-with-kthread_func-check.patch

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

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Kefeng Wang <wangkefeng.wang@huawei.com>
Subject: mm: replace PF_KCOMPACTD flag with kthread_func() check
Date: Wed, 2 Sep 2026 21:16:53 +0800

PF_KCOMPACTD was introduced by commit ce6d9c1c2b5c ("NFS: fix
nfs_release_folio() to not deadlock via kcompactd writeback") so
nfs_release_folio() could detect kcompactd context and skip writeback. 
The flag is only consumed by current_is_kcompactd(), whose sole caller is
nfs_release_folio().

Replace the flag-based check with kthread_func(current) == kcompactd,
freeing the 0x00010000 PF flag bit.

Link: https://lore.kernel.org/20260902131653.1338227-5-wangkefeng.wang@huawei.com
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Zi Yan <ziy@nvidia.com>
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Cc: Brendan Jackman <brendan.jackman@linux.dev>
Cc: Carlos Maiolino <cem@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: "Darrick J. Wong" <djwong@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/compaction.h               |   11 ++++++-----
 include/linux/sched.h                    |    2 +-
 mm/compaction.c                          |    9 ++++++---
 tools/sched_ext/include/scx/common.bpf.h |    1 -
 4 files changed, 13 insertions(+), 10 deletions(-)

--- a/include/linux/compaction.h~mm-replace-pf_kcompactd-flag-with-kthread_func-check
+++ a/include/linux/compaction.h
@@ -81,10 +81,6 @@ static inline unsigned long compact_gap(
 	return min(2UL << order, COMPACT_CLUSTER_MAX);
 }
 
-static inline int current_is_kcompactd(void)
-{
-	return current->flags & PF_KCOMPACTD;
-}
 
 #ifdef CONFIG_COMPACTION
 
@@ -103,7 +99,7 @@ extern void compaction_defer_reset(struc
 
 bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
 					int alloc_flags, gfp_t gfp_mask);
-
+bool current_is_kcompactd(void);
 extern void __meminit kcompactd_run(int nid);
 extern void __meminit kcompactd_stop(int nid);
 extern void wakeup_kcompactd(pg_data_t *pgdat, int order, int highest_zoneidx);
@@ -119,6 +115,11 @@ static inline bool compaction_suitable(s
 {
 	return false;
 }
+
+static inline bool current_is_kcompactd(void)
+{
+	return false;
+}
 
 static inline void kcompactd_run(int nid)
 {
--- a/include/linux/sched.h~mm-replace-pf_kcompactd-flag-with-kthread_func-check
+++ a/include/linux/sched.h
@@ -1808,7 +1808,7 @@ extern struct pid *cad_pid;
 #define PF_USED_MATH		0x00002000	/* If unset the fpu must be initialized before use */
 #define PF_USER_WORKER		0x00004000	/* Kernel thread cloned from userspace thread */
 #define PF_NOFREEZE		0x00008000	/* This thread should not be frozen */
-#define PF_KCOMPACTD		0x00010000	/* I am kcompactd */
+#define PF__HOLE__00010000	0x00010000
 #define PF__HOLE__00020000	0x00020000
 #define PF_MEMALLOC_NOFS	0x00040000	/* All allocations inherit GFP_NOFS. See memalloc_nfs_save() */
 #define PF_MEMALLOC_NOIO	0x00080000	/* All allocations inherit GFP_NOIO. See memalloc_noio_save() */
--- a/mm/compaction.c~mm-replace-pf_kcompactd-flag-with-kthread_func-check
+++ a/mm/compaction.c
@@ -3197,7 +3197,6 @@ static int kcompactd(void *p)
 	long default_timeout = msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC);
 	long timeout = default_timeout;
 
-	current->flags |= PF_KCOMPACTD;
 	set_freezable();
 
 	pgdat->kcompactd_max_order = 0;
@@ -3254,11 +3253,15 @@ static int kcompactd(void *p)
 			pgdat->proactive_compact_trigger = false;
 	}
 
-	current->flags &= ~PF_KCOMPACTD;
-
 	return 0;
 }
 
+bool current_is_kcompactd(void)
+{
+	return kthread_func(current) == kcompactd;
+}
+EXPORT_SYMBOL_GPL(current_is_kcompactd);
+
 /*
  * This kcompactd start function will be called by init and node-hot-add.
  * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added.
--- a/tools/sched_ext/include/scx/common.bpf.h~mm-replace-pf_kcompactd-flag-with-kthread_func-check
+++ a/tools/sched_ext/include/scx/common.bpf.h
@@ -31,7 +31,6 @@
 #define PF_IDLE				0x00000002	/* I am an IDLE thread */
 #define PF_IO_WORKER			0x00000010	/* Task is an IO worker */
 #define PF_WQ_WORKER			0x00000020	/* I'm a workqueue worker */
-#define PF_KCOMPACTD			0x00010000      /* I am kcompactd */
 #define PF_KTHREAD			0x00200000	/* I am a kernel thread */
 #define PF_EXITING			0x00000004
 #define CLOCK_MONOTONIC			1
_

Patches currently in -mm which might be from wangkefeng.wang@huawei.com are

xfs-remove-dead-kswapd-flag-inheritance-from-btree-split-worker.patch
iomap-simplify-writepages-reclaim-guard.patch
mm-replace-pf_kswapd-flag-with-kthread_func-check.patch
mm-replace-pf_kcompactd-flag-with-kthread_func-check.patch