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

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Date:   Thu, 5 Aug 2021 17:43:04 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     SeongJae Park <sj38.park@...il.com>
Cc:     SeongJae Park <sjpark@...zon.de>, Jonathan.Cameron@...wei.com,
        acme@...nel.org, alexander.shishkin@...ux.intel.com,
        amit@...nel.org, benh@...nel.crashing.org,
        brendanhiggins@...gle.com, corbet@....net, david@...hat.com,
        dwmw@...zon.com, elver@...gle.com, fan.du@...el.com,
        foersleo@...zon.de, greg@...ah.com, gthelen@...gle.com,
        guoju.fgj@...baba-inc.com, jgowans@...zon.com, joe@...ches.com,
        mgorman@...e.de, mheyne@...zon.de, minchan@...nel.org,
        mingo@...hat.com, namhyung@...nel.org, peterz@...radead.org,
        riel@...riel.com, rientjes@...gle.com, rostedt@...dmis.org,
        rppt@...nel.org, shakeelb@...gle.com, shuah@...nel.org,
        sieberf@...zon.com, snu@...le79.org, vbabka@...e.cz,
        vdavydov.dev@...il.com, zgf574564920@...il.com,
        linux-damon@...zon.com, linux-mm@...ck.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v34 07/13] mm/damon: Implement a debugfs-based user
 space interface

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

> From: SeongJae Park <sjpark@...zon.de>
> 
> 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;
_