[RFC PATCH v4 01/10] mm/damon/core: introduce damon_ctx->paused

[SeongJae Park]

DAMON supports only start and stop of the execution.  When it is
stopped, its internal data that it self-trained goes away.  It will be
useful if the execution can be paused and resumed with the previous
self-trained data.

Introduce per-context API parameter, 'paused', for the purpose.  The
parameter can be set and unset while DAMON is running and paused, using
the online parameters commit helper functions (damon_commit_ctx() and
damon_call()).  Once 'paused' is set, the kdamond_fn() main loop does
only limited works with sampling interval sleep during the works.  The
limited works include the handling of the online parameters update, so
that users can unset the 'pause' and resume the execution when they
want.  It also keep checking DAMON stop conditions and handling of it,
so that DAMON can be stopped while paused if needed.

Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
---
 include/linux/damon.h | 2 ++
 mm/damon/core.c       | 9 +++++++++
 2 files changed, 11 insertions(+)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index d9a3babbafc16..ea1649a09395d 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -787,6 +787,7 @@ struct damon_attrs {
  * @ops:	Set of monitoring operations for given use cases.
  * @addr_unit:	Scale factor for core to ops address conversion.
  * @min_region_sz:	Minimum region size.
+ * @pause:	Pause kdamond main loop.
  * @adaptive_targets:	Head of monitoring targets (&damon_target) list.
  * @schemes:		Head of schemes (&damos) list.
  */
@@ -838,6 +839,7 @@ struct damon_ctx {
 	struct damon_operations ops;
 	unsigned long addr_unit;
 	unsigned long min_region_sz;
+	bool pause;
 
 	struct list_head adaptive_targets;
 	struct list_head schemes;
diff --git a/mm/damon/core.c b/mm/damon/core.c
index db6c67e52d2b8..0ab2cfa848e69 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -1349,6 +1349,7 @@ int damon_commit_ctx(struct damon_ctx *dst, struct damon_ctx *src)
 		if (err)
 			return err;
 	}
+	dst->pause = src->pause;
 	dst->ops = src->ops;
 	dst->addr_unit = src->addr_unit;
 	dst->min_region_sz = src->min_region_sz;
@@ -3003,6 +3004,14 @@ static int kdamond_fn(void *data)
 		kdamond_call(ctx, false);
 		if (ctx->maybe_corrupted)
 			break;
+		while (ctx->pause) {
+			damos_walk_cancel(ctx);
+			kdamond_usleep(ctx->attrs.sample_interval);
+			/* allow caller unset pause via damon_call() */
+			kdamond_call(ctx, false);
+			if (kdamond_need_stop(ctx) || ctx->maybe_corrupted)
+				goto done;
+		}
 		if (!list_empty(&ctx->schemes))
 			kdamond_apply_schemes(ctx);
 		else
-- 
2.47.3