Re: [PATCH v34 07/13] mm/damon: Implement a debugfs-based user space interface

[Andrew Morton]

On Fri, 16 Jul 2021 08:14:43 +0000 SeongJae Park <sj38.park@xxxxxxxxx> wrote:

> From: SeongJae Park <sjpark@xxxxxxxxx>
> 
> DAMON is designed to be used by kernel space code such as the memory
> management subsystems, and therefore it provides only kernel space API.
> That said, letting the user space control DAMON could provide some
> benefits to them.  For example, it will allow user space to analyze
> their specific workloads and make their own special optimizations.
> 
> For such cases, this commit implements a simple DAMON application kernel
> module, namely 'damon-dbgfs', which merely wraps the DAMON api and
> exports those to the user space via the debugfs.
> 
> ...
>
> +static int __init damon_dbgfs_init(void)
> +{
> +	int rc;
> +
> +	dbgfs_ctxs = kmalloc(sizeof(*dbgfs_ctxs), GFP_KERNEL);
> +	if (!dbgfs_ctxs) {
> +		pr_err("%s: dbgfs ctxs alloc failed\n", __func__);
> +		return -ENOMEM;
> +	}
> +	dbgfs_ctxs[0] = dbgfs_new_ctx();
> +	if (!dbgfs_ctxs[0]) {
> +		kfree(dbgfs_ctxs);
> +		pr_err("%s: dbgfs ctx alloc failed\n", __func__);
> +		return -ENOMEM;
> +	}

checkpatch points out that the "alloc failed" messages are unneeded -
kmalloc(GFP_KERNEL) will have already emitted a stack trace.  Is this
fixup OK?

--- a/mm/damon/dbgfs.c~mm-damon-implement-a-debugfs-based-user-space-interface-fix
+++ a/mm/damon/dbgfs.c
@@ -373,14 +373,11 @@ static int __init damon_dbgfs_init(void)
 	int rc;
 
 	dbgfs_ctxs = kmalloc(sizeof(*dbgfs_ctxs), GFP_KERNEL);
-	if (!dbgfs_ctxs) {
-		pr_err("%s: dbgfs ctxs alloc failed\n", __func__);
+	if (!dbgfs_ctxs)
 		return -ENOMEM;
-	}
 	dbgfs_ctxs[0] = dbgfs_new_ctx();
 	if (!dbgfs_ctxs[0]) {
 		kfree(dbgfs_ctxs);
-		pr_err("%s: dbgfs ctx alloc failed\n", __func__);
 		return -ENOMEM;
 	}
 	dbgfs_nr_ctxs = 1;
_