linux-kernel - [PATCH V9 2/8] fork/vm: Move common PF_IO

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Date:   Thu, 12 May 2022 16:46:58 -0500
From:   Mike Christie <michael.christie@...cle.com>
To:     hch@...radead.org, stefanha@...hat.com, jasowang@...hat.com,
        mst@...hat.com, sgarzare@...hat.com,
        virtualization@...ts.linux-foundation.org, brauner@...nel.org,
        ebiederm@...ssion.com, linux-kernel@...r.kernel.org
Cc:     Mike Christie <michael.christie@...cle.com>
Subject: [PATCH V9 2/8] fork/vm: Move common PF_IO_WORKER behavior to new flag

This adds a new flag, PF_USER_WORKER, that's used for behavior common to
to both PF_IO_WORKER and users like vhost which will use a new helper
instead of create_io_thread because they require different behavior for
operations like signal handling.

The common behavior PF_USER_WORKER covers is the vm reclaim handling.

Signed-off-by: Mike Christie <michael.christie@...cle.com>
---
 include/linux/sched.h      | 1 +
 include/linux/sched/task.h | 3 ++-
 kernel/fork.c              | 4 ++++
 mm/vmscan.c                | 4 ++--
 4 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a8911b1f35aa..0fa66a098183 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1700,6 +1700,7 @@ extern struct pid *cad_pid;
 #define PF_MEMALLOC		0x00000800	/* Allocating memory */
 #define PF_NPROC_EXCEEDED	0x00001000	/* set_user() noticed that RLIMIT_NPROC was exceeded */
 #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_FROZEN		0x00010000	/* Frozen for system suspend */
 #define PF_KSWAPD		0x00020000	/* I am kswapd */
diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index b0a9d6c75bcc..9e20fa18c41f 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -18,7 +18,8 @@ struct css_set;
 /* All the bits taken by the old clone syscall. */
 #define CLONE_LEGACY_FLAGS 0xffffffffULL
 
-#define USER_WORKER_IO		BIT(0)
+#define USER_WORKER		BIT(0)
+#define USER_WORKER_IO		BIT(1)
 
 struct kernel_clone_args {
 	u64 flags;
diff --git a/kernel/fork.c b/kernel/fork.c
index f4f2c88d9a2a..19293bcca001 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2071,6 +2071,10 @@ static __latent_entropy struct task_struct *copy_process(
 	p->flags &= ~PF_KTHREAD;
 	if (args->kthread)
 		p->flags |= PF_KTHREAD;
+
+	if (args->worker_flags & USER_WORKER)
+		p->flags |= PF_USER_WORKER;
+
 	if (args->worker_flags & USER_WORKER_IO) {
 		/*
 		 * Mark us an IO worker, and block any signal that isn't
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1678802e03e7..0f58587862ef 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1051,12 +1051,12 @@ void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason)
 	DEFINE_WAIT(wait);
 
 	/*
-	 * Do not throttle IO workers, kthreads other than kswapd or
+	 * Do not throttle user workers, kthreads other than kswapd or
 	 * workqueues. They may be required for reclaim to make
 	 * forward progress (e.g. journalling workqueues or kthreads).
 	 */
 	if (!current_is_kswapd() &&
-	    current->flags & (PF_IO_WORKER|PF_KTHREAD)) {
+	    current->flags & (PF_USER_WORKER|PF_KTHREAD)) {
 		cond_resched();
 		return;
 	}
-- 
2.25.1