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SubjectRe: [PATCH 1/7] mm/damon/dbgfs: Allow users to set initial monitoring target regions
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On Wed, 13 Oct 2021 15:45:35 -0700 Andrew Morton <akpm@linux-foundation.org> wrote:

> On Tue, 12 Oct 2021 20:57:05 +0000 SeongJae Park <sj@kernel.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;
> > +}
> > +
>
>

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