[patch 260/262] mm/damon: simplify stop mechanism

Andrew Morton
2021-11-05T20:48:24Z

From: Changbin Du <changbin.du@gmail.com>
Subject: mm/damon: simplify stop mechanism

A kernel thread can exit gracefully with kthread_stop(). So we don't need
a new flag 'kdamond_stop'. And to make sure the task struct is not freed
when accessing it, get reference to it before termination.

Link: https://lkml.kernel.org/r/20211027130517.4404-1-changbin.du@gmail.com
Signed-off-by: Changbin Du <changbin.du@gmail.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

include/linux/damon.h | 1
mm/damon/core.c | 51 +++++++++++-----------------------------
2 files changed, 15 insertions(+), 37 deletions(-)

--- a/include/linux/damon.h~mm-damon-simplify-stop-mechanism
+++ a/include/linux/damon.h
@@ -381,7 +381,6 @@ struct damon_ctx {

/* public: */
struct task_struct *kdamond;
- bool kdamond_stop;
struct mutex kdamond_lock;

struct damon_primitive primitive;
--- a/mm/damon/core.c~mm-damon-simplify-stop-mechanism
+++ a/mm/damon/core.c
@@ -390,17 +390,6 @@ static unsigned long damon_region_sz_lim
return sz;
}

-static bool damon_kdamond_running(struct damon_ctx *ctx)
-{
- bool running;
-
- mutex_lock(&ctx->kdamond_lock);
- running = ctx->kdamond != NULL;
- mutex_unlock(&ctx->kdamond_lock);
-
- return running;
-}
-
static int kdamond_fn(void *data);

/*
@@ -418,7 +407,6 @@ static int __damon_start(struct damon_ct
mutex_lock(&ctx->kdamond_lock);
if (!ctx->kdamond) {
err = 0;
- ctx->kdamond_stop = false;
ctx->kdamond = kthread_run(kdamond_fn, ctx, "kdamond.%d",
nr_running_ctxs);
if (IS_ERR(ctx->kdamond)) {
@@ -474,13 +462,15 @@ int damon_start(struct damon_ctx **ctxs,
*/
static int __damon_stop(struct damon_ctx *ctx)
{
+ struct task_struct *tsk;
+
mutex_lock(&ctx->kdamond_lock);
- if (ctx->kdamond) {
- ctx->kdamond_stop = true;
+ tsk = ctx->kdamond;
+ if (tsk) {
+ get_task_struct(tsk);
mutex_unlock(&ctx->kdamond_lock);
- while (damon_kdamond_running(ctx))
- usleep_range(ctx->sample_interval,
- ctx->sample_interval * 2);
+ kthread_stop(tsk);
+ put_task_struct(tsk);
return 0;
}
mutex_unlock(&ctx->kdamond_lock);
@@ -925,12 +915,8 @@ static bool kdamond_need_update_primitiv
static bool kdamond_need_stop(struct damon_ctx *ctx)
{
struct damon_target *t;
- bool stop;

- mutex_lock(&ctx->kdamond_lock);
- stop = ctx->kdamond_stop;
- mutex_unlock(&ctx->kdamond_lock);
- if (stop)
+ if (kthread_should_stop())
return true;

if (!ctx->primitive.target_valid)
@@ -1021,13 +1007,6 @@ static int kdamond_wait_activation(struc
return -EBUSY;
}

-static void set_kdamond_stop(struct damon_ctx *ctx)
-{
- mutex_lock(&ctx->kdamond_lock);
- ctx->kdamond_stop = true;
- mutex_unlock(&ctx->kdamond_lock);
-}
-
/*
* The monitoring daemon that runs as a kernel thread
*/
@@ -1038,17 +1017,18 @@ static int kdamond_fn(void *data)
struct damon_region *r, *next;
unsigned int max_nr_accesses = 0;
unsigned long sz_limit = 0;
+ bool done = false;

pr_debug("kdamond (%d) starts\n", current->pid);

if (ctx->primitive.init)
ctx->primitive.init(ctx);
if (ctx->callback.before_start && ctx->callback.before_start(ctx))
- set_kdamond_stop(ctx);
+ done = true;

sz_limit = damon_region_sz_limit(ctx);

- while (!kdamond_need_stop(ctx)) {
+ while (!kdamond_need_stop(ctx) && !done) {
if (kdamond_wait_activation(ctx))
continue;

@@ -1056,7 +1036,7 @@ static int kdamond_fn(void *data)
ctx->primitive.prepare_access_checks(ctx);
if (ctx->callback.after_sampling &&
ctx->callback.after_sampling(ctx))
- set_kdamond_stop(ctx);
+ done = true;

usleep_range(ctx->sample_interval, ctx->sample_interval + 1);

@@ -1069,7 +1049,7 @@ static int kdamond_fn(void *data)
sz_limit);
if (ctx->callback.after_aggregation &&
ctx->callback.after_aggregation(ctx))
- set_kdamond_stop(ctx);
+ done = true;
kdamond_apply_schemes(ctx);
kdamond_reset_aggregated(ctx);
kdamond_split_regions(ctx);
@@ -1088,9 +1068,8 @@ static int kdamond_fn(void *data)
damon_destroy_region(r, t);
}

- if (ctx->callback.before_terminate &&
- ctx->callback.before_terminate(ctx))
- set_kdamond_stop(ctx);
+ if (ctx->callback.before_terminate)
+ ctx->callback.before_terminate(ctx);
if (ctx->primitive.cleanup)
ctx->primitive.cleanup(ctx);

_