On Tue, 31 May 2022 20:22:27 -0700 Roman Gushchin <roman.gushchin@xxxxxxxxx> wrote:
> Add a scan interface which allows to trigger scanning of a particular
> shrinker and specify memcg and numa node. It's useful for testing,
> debugging and profiling of a specific scan_objects() callback.
> Unlike alternatives (creating a real memory pressure and dropping
> caches via /proc/sys/vm/drop_caches) this interface allows to interact
> with only one shrinker at once. Also, if a shrinker is misreporting
> the number of objects (as some do), it doesn't affect scanning.
>
> ..
>
> --- a/mm/shrinker_debug.c
> +++ b/mm/shrinker_debug.c
> @@ -99,6 +99,78 @@ static int shrinker_debugfs_count_show(struct seq_file *m, void *v)
> }
> DEFINE_SHOW_ATTRIBUTE(shrinker_debugfs_count);
>
> +static int shrinker_debugfs_scan_open(struct inode *inode, struct file *file)
> +{
> + file->private_data = inode->i_private;
> + return nonseekable_open(inode, file);
> +}
> +
> +static ssize_t shrinker_debugfs_scan_write(struct file *file,
> + const char __user *buf,
> + size_t size, loff_t *pos)
> +{
> + struct shrinker *shrinker = file->private_data;
> + unsigned long nr_to_scan = 0, ino;
> + struct shrink_control sc = {
> + .gfp_mask = GFP_KERNEL,
> + };
> + struct mem_cgroup *memcg = NULL;
> + int nid;
> + char kbuf[72];
> + int read_len = size < (sizeof(kbuf) - 1) ? size : (sizeof(kbuf) - 1);
size_t or ulong would be more appropriate.
> + ssize_t ret;
> +
> + if (copy_from_user(kbuf, buf, read_len))
> + return -EFAULT;
> + kbuf[read_len] = '\0';
> +
> + if (sscanf(kbuf, "%lu %d %lu", &ino, &nid, &nr_to_scan) < 2)
Was it intentional to permit more than three args?
> + return -EINVAL;
> +
> + if (nid < 0 || nid >= nr_node_ids)
> + return -EINVAL;
> +
> + if (nr_to_scan == 0)
> + return size;
> +
> + if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
> + memcg = mem_cgroup_get_from_ino(ino);
> + if (!memcg || IS_ERR(memcg))
> + return -ENOENT;
> +
> + if (!mem_cgroup_online(memcg)) {
> + mem_cgroup_put(memcg);
> + return -ENOENT;
> + }
> + } else if (ino != 0) {
> + return -EINVAL;
> + }
> +
> + ret = down_read_killable(&shrinker_rwsem);
> + if (ret) {
> + mem_cgroup_put(memcg);
> + return ret;
> + }
> +
> + sc.nid = nid;
> + sc.memcg = memcg;
> + sc.nr_to_scan = nr_to_scan;
> + sc.nr_scanned = nr_to_scan;
> +
> + shrinker->scan_objects(shrinker, &sc);
> +
> + up_read(&shrinker_rwsem);
> + mem_cgroup_put(memcg);
> +
> + return size;
> +}
