From 44b74ec3ae5ac2f7773d5656e43aae7b29303b74 Mon Sep 17 00:00:00 2001 From: Kefeng Wang Date: Wed, 2 Sep 2026 21:16:53 +0800 Subject: [PATCH] mm: replace PF_KCOMPACTD flag with kthread_func() check 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 Signed-off-by: Andrew Morton Acked-by: Shakeel Butt Acked-by: Zi Yan Acked-by: Vlastimil Babka (SUSE) Reviewed-by: David Hildenbrand (Arm) Cc: Brendan Jackman Cc: Carlos Maiolino Cc: Christian Brauner Cc: Christoph Hellwig Cc: "Darrick J. Wong" Cc: Johannes Weiner Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Suren Baghdasaryan --- 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(-) diff --git a/include/linux/compaction.h b/include/linux/compaction.h index 66a2f70e9e01..691c09f0a697 100644 --- a/include/linux/compaction.h +++ b/include/linux/compaction.h @@ -81,10 +81,6 @@ static inline unsigned long compact_gap(unsigned int order) 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(struct zone *zone, int order, 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); @@ -120,6 +116,11 @@ static inline bool compaction_suitable(struct zone *zone, int order, return false; } +static inline bool current_is_kcompactd(void) +{ + return false; +} + static inline void kcompactd_run(int nid) { } diff --git a/include/linux/sched.h b/include/linux/sched.h index 90393bd53bbc..f45b7d43113c 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1809,7 +1809,7 @@ extern struct pid __rcu *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() */ diff --git a/mm/compaction.c b/mm/compaction.c index a049415512c6..4994e200bbec 100644 --- a/mm/compaction.c +++ b/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. diff --git a/tools/sched_ext/include/scx/common.bpf.h b/tools/sched_ext/include/scx/common.bpf.h index 5a28a36c5120..ab8d676d8cd6 100644 --- a/tools/sched_ext/include/scx/common.bpf.h +++ b/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