linux-kernel - Re: [PATCH 1/7] mm/damon/dbgfs: Allow users to set initial monitoring target regions

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Message-Id: <20211014064522.24455-1-sj@kernel.org>
Date:   Thu, 14 Oct 2021 06:45:22 +0000
From:   SeongJae Park <sj@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     SeongJae Park <sj@...nel.org>, Jonathan.Cameron@...wei.com,
        amit@...nel.org, benh@...nel.crashing.org, corbet@....net,
        david@...hat.com, dwmw@...zon.com, elver@...gle.com,
        foersleo@...zon.de, gthelen@...gle.com, markubo@...zon.de,
        rientjes@...gle.com, shakeelb@...gle.com, shuah@...nel.org,
        linux-damon@...zon.com, linux-mm@...ck.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] mm/damon/dbgfs: Allow users to set initial monitoring target regions

On Wed, 13 Oct 2021 15:45:35 -0700 Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Tue, 12 Oct 2021 20:57:05 +0000 SeongJae Park <sj@...nel.org> wrote:
> 
> > Some 'damon-dbgfs' users would want to monitor only a part of the entire
> > virtual memory address space.  The program interface users in the kernel
> > space could use '->before_start()' callback or set the regions inside
> > the context struct as they want, but 'damon-dbgfs' users cannot.
> > 
> > For the reason, this commit introduces a new debugfs file called
> > 'init_region'.  'damon-dbgfs' users can specify which initial monitoring
> > target address regions they want by writing special input to the file.
> > The input should describe each region in each line in the below form:
> > 
> >     <pid> <start address> <end address>
> > 
> > Note that the regions will be updated to cover entire memory mapped
> > regions after a 'regions update interval' is passed.  If you want the
> > regions to not be updated after the initial setting, you could set the
> > interval as a very long time, say, a few decades.
> > 
> > ...
> >
> > +static int add_init_region(struct damon_ctx *c,
> > +			 unsigned long target_id, struct damon_addr_range *ar)
> > +{
> > +	struct damon_target *t;
> > +	struct damon_region *r, *prev;
> > +	unsigned long id;
> > +	int rc = -EINVAL;
> > +
> > +	if (ar->start >= ar->end)
> > +		return -EINVAL;
> > +
> > +	damon_for_each_target(t, c) {
> > +		id = t->id;
> > +		if (targetid_is_pid(c))
> > +			id = (unsigned long)pid_vnr((struct pid *)id);
> 
> This is a bit ugly.  Did you consider making damon_target.id a union of
> all the possible types it can contain?  This will avoid typecasts, has
> documentation value and reflacts what is actually going on.

Agreed, thank you for this great comment!  I will make it at least before
adding another type of monitoring target.


Thanks,
SJ

> 
> > +		if (id == target_id) {
> > +			r = damon_new_region(ar->start, ar->end);
> > +			if (!r)
> > +				return -ENOMEM;
> > +			damon_add_region(r, t);
> > +			if (damon_nr_regions(t) > 1) {
> > +				prev = damon_prev_region(r);
> > +				if (prev->ar.end > r->ar.start) {
> > +					damon_destroy_region(r, t);
> > +					return -EINVAL;
> > +				}
> > +			}
> > +			rc = 0;
> > +		}
> > +	}
> > +	return rc;
> > +}
> > +
> 
>