[PATCH] mm/damon/core: Optimize kdamod.%d thread creation code

From: Xin Hao
Date: Sat Oct 16 2021 - 12:59:34 EST


When the ctx->adaptive_targets list is empty,
i did some test on monitor_on interface like this.

echo on > /sys/kernel/debug/damon/monitor_on
[ 851.988307] damon: kdamond (5390) starts

Though the ctx->adaptive_targets list is empty, but the
kthread_run still be called, and the kdamond.x thread still
be created, this is meaningless, so t

So there adds a judgment. only if the ctx->adaptive_targets
list is not empty, and ctx->kdamond pointer is NULL, then call
the __damon_start function.

Signed-off-by: Xin Hao <xhao@xxxxxxxxxxxxxxxxx>
---
mm/damon/core.c | 30 ++++++++++++++++++------------
1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 30e9211f494a..998c707fdca2 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -107,6 +107,11 @@ void damon_add_target(struct damon_ctx *ctx, struct damon_target *t)
list_add_tail(&t->list, &ctx->adaptive_targets);
}

+static int damon_target_empty(struct damon_ctx *ctx)
+{
+ return list_empty(&ctx->adaptive_targets);
+}
+
static void damon_del_target(struct damon_target *t)
{
list_del(&t->list);
@@ -307,15 +312,14 @@ static int __damon_start(struct damon_ctx *ctx)
int err = -EBUSY;

mutex_lock(&ctx->kdamond_lock);
- if (!ctx->kdamond) {
+ ctx->kdamond_stop = false;
+ ctx->kdamond = kthread_run(kdamond_fn, ctx, "kdamond.%d",
+ nr_running_ctxs);
+ if (IS_ERR(ctx->kdamond)) {
+ err = PTR_ERR(ctx->kdamond);
+ ctx->kdamond = 0;
+ } else {
err = 0;
- ctx->kdamond_stop = false;
- ctx->kdamond = kthread_run(kdamond_fn, ctx, "kdamond.%d",
- nr_running_ctxs);
- if (IS_ERR(ctx->kdamond)) {
- err = PTR_ERR(ctx->kdamond);
- ctx->kdamond = 0;
- }
}
mutex_unlock(&ctx->kdamond_lock);

@@ -347,10 +351,12 @@ int damon_start(struct damon_ctx **ctxs, int nr_ctxs)
}

for (i = 0; i < nr_ctxs; i++) {
- err = __damon_start(ctxs[i]);
- if (err)
- break;
- nr_running_ctxs++;
+ if (!damon_target_empty(ctxs[i]) && !ctxs[i]->kdamond) {
+ err = __damon_start(ctxs[i]);
+ if (err)
+ break;
+ nr_running_ctxs++;
+ }
}
mutex_unlock(&damon_lock);

--
2.31.0