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

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Message-Id: <20210806114645.6777-1-sjpark@amazon.de>
Date:   Fri,  6 Aug 2021 11:46:44 +0000
From:   SeongJae Park <sj38.park@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     SeongJae Park <sj38.park@...il.com>,
        SeongJae Park <sjpark@...zon.de>, Jonathan.Cameron@...wei.com,
        acme@...nel.org, alexander.shishkin@...ux.intel.com,
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Subject: Re: [PATCH v34 07/13] mm/damon: Implement a debugfs-based user space interface

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

On Thu, 5 Aug 2021 17:43:04 -0700 Andrew Morton <akpm@...ux-foundation.org> wrote:

> 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?

Yes, of course.  I also see you already kindly applied this in the -mm tree[1],
appreciate!

[1] https://www.ozlabs.org/~akpm/mmotm/broken-out/mm-damon-implement-a-debugfs-based-user-space-interface-fix.patch


Thanks,
SeongJae Park

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