[PATCH v3 01/13] mm/damon/core: Allow non-exclusive DAMON start/stop

SeongJae Park
2022-02-28T08:13:32Z

To avoid interference between DAMON contexts monitoring overlapping
memory regions, damon_start() works in an exclusive manner. That is,
damon_start() does nothing bug fails if any context that started by
another instance of the function is still running. This makes its
usage a little bit restrictive. However, admins could aware each DAMON
usage and address such interferences on their own in some cases.

This commit hence implements non-exclusive mode of the function and
allows the callers to select the mode. Note that the exclusive groups
and non-exclusive groups of contexts will respect each other in a manner
similar to that of reader-writer locks. Therefore, this commit will not
cause any behavioral change to the exclusive groups.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
include/linux/damon.h | 2 +-
mm/damon/core.c | 23 +++++++++++++++--------
mm/damon/dbgfs.c | 2 +-
mm/damon/reclaim.c | 2 +-
4 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 49c4a11ecf20..f8e99e47d747 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -508,7 +508,7 @@ int damon_nr_running_ctxs(void);
int damon_register_ops(struct damon_operations *ops);
int damon_select_ops(struct damon_ctx *ctx, enum damon_ops_id id);

-int damon_start(struct damon_ctx **ctxs, int nr_ctxs);
+int damon_start(struct damon_ctx **ctxs, int nr_ctxs, bool exclusive);
int damon_stop(struct damon_ctx **ctxs, int nr_ctxs);

#endif /* CONFIG_DAMON */
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 82e0a4620c4f..c1e0fed4e877 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -24,6 +24,7 @@

static DEFINE_MUTEX(damon_lock);
static int nr_running_ctxs;
+static bool running_exclusive_ctxs;

static DEFINE_MUTEX(damon_ops_lock);
static struct damon_operations damon_registered_ops[NR_DAMON_OPS];
@@ -434,22 +435,25 @@ static int __damon_start(struct damon_ctx *ctx)
* damon_start() - Starts the monitorings for a given group of contexts.
* @ctxs: an array of the pointers for contexts to start monitoring
* @nr_ctxs: size of @ctxs
+ * @exclusive: exclusiveness of this contexts group
*
* This function starts a group of monitoring threads for a group of monitoring
* contexts. One thread per each context is created and run in parallel. The
- * caller should handle synchronization between the threads by itself. If a
- * group of threads that created by other 'damon_start()' call is currently
- * running, this function does nothing but returns -EBUSY.
+ * caller should handle synchronization between the threads by itself. If
+ * @exclusive is true and a group of threads that created by other
+ * 'damon_start()' call is currently running, this function does nothing but
+ * returns -EBUSY.
*
* Return: 0 on success, negative error code otherwise.
*/
-int damon_start(struct damon_ctx **ctxs, int nr_ctxs)
+int damon_start(struct damon_ctx **ctxs, int nr_ctxs, bool exclusive)
{
int i;
int err = 0;

mutex_lock(&damon_lock);
- if (nr_running_ctxs) {
+ if ((exclusive && nr_running_ctxs) ||
+ (!exclusive && running_exclusive_ctxs)) {
mutex_unlock(&damon_lock);
return -EBUSY;
}
@@ -460,13 +464,15 @@ int damon_start(struct damon_ctx **ctxs, int nr_ctxs)
break;
nr_running_ctxs++;
}
+ if (exclusive && nr_running_ctxs)
+ running_exclusive_ctxs = true;
mutex_unlock(&damon_lock);

return err;
}

/*
- * __damon_stop() - Stops monitoring of given context.
+ * __damon_stop() - Stops monitoring of a given context.
* @ctx: monitoring context
*
* Return: 0 on success, negative error code otherwise.
@@ -504,9 +510,8 @@ int damon_stop(struct damon_ctx **ctxs, int nr_ctxs)
/* nr_running_ctxs is decremented in kdamond_fn */
err = __damon_stop(ctxs[i]);
if (err)
- return err;
+ break;
}
-
return err;
}

@@ -1102,6 +1107,8 @@ static int kdamond_fn(void *data)

mutex_lock(&damon_lock);
nr_running_ctxs--;
+ if (!nr_running_ctxs && running_exclusive_ctxs)
+ running_exclusive_ctxs = false;
mutex_unlock(&damon_lock);

return 0;
diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index 05b574cbcea8..a0dab8b5e45f 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -967,7 +967,7 @@ static ssize_t dbgfs_monitor_on_write(struct file *file,
return -EINVAL;
}
}
- ret = damon_start(dbgfs_ctxs, dbgfs_nr_ctxs);
+ ret = damon_start(dbgfs_ctxs, dbgfs_nr_ctxs, true);
} else if (!strncmp(kbuf, "off", count)) {
ret = damon_stop(dbgfs_ctxs, dbgfs_nr_ctxs);
} else {
diff --git a/mm/damon/reclaim.c b/mm/damon/reclaim.c
index b53d9c22fad1..e34c4d0c4d93 100644
--- a/mm/damon/reclaim.c
+++ b/mm/damon/reclaim.c
@@ -330,7 +330,7 @@ static int damon_reclaim_turn(bool on)
if (err)
goto free_scheme_out;

- err = damon_start(&ctx, 1);
+ err = damon_start(&ctx, 1, true);
if (!err) {
kdamond_pid = ctx->kdamond->pid;
return 0;
--
2.17.1