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Date: Tue, 2 Feb 2021 11:00:13 +0100
From: SeongJae Park <sjpark@...zon.com>
To: Shakeel Butt <shakeelb@...gle.com>
CC: SeongJae Park <sjpark@...zon.com>,
SeongJae Park <sjpark@...zon.de>,
<Jonathan.Cameron@...wei.com>,
Andrea Arcangeli <aarcange@...hat.com>, <acme@...nel.org>,
<alexander.shishkin@...ux.intel.com>, <amit@...nel.org>,
<benh@...nel.crashing.org>, <brendan.d.gregg@...il.com>,
Brendan Higgins <brendanhiggins@...gle.com>,
Qian Cai <cai@....pw>,
Colin Ian King <colin.king@...onical.com>,
Jonathan Corbet <corbet@....net>,
"David Hildenbrand" <david@...hat.com>, <dwmw@...zon.com>,
Marco Elver <elver@...gle.com>, "Du, Fan" <fan.du@...el.com>,
<foersleo@...zon.de>, "Greg Thelen" <gthelen@...gle.com>,
Ian Rogers <irogers@...gle.com>, <jolsa@...hat.com>,
"Kirill A. Shutemov" <kirill@...temov.name>,
Mark Rutland <mark.rutland@....com>,
Mel Gorman <mgorman@...e.de>, Minchan Kim <minchan@...nel.org>,
Ingo Molnar <mingo@...hat.com>, <namhyung@...nel.org>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Randy Dunlap <rdunlap@...radead.org>,
Rik van Riel <riel@...riel.com>,
David Rientjes <rientjes@...gle.com>,
Steven Rostedt <rostedt@...dmis.org>,
Mike Rapoport <rppt@...nel.org>, <sblbir@...zon.com>,
Shuah Khan <shuah@...nel.org>, <sj38.park@...il.com>,
<snu@...zon.de>, Vlastimil Babka <vbabka@...e.cz>,
Vladimir Davydov <vdavydov.dev@...il.com>,
Yang Shi <yang.shi@...ux.alibaba.com>,
Huang Ying <ying.huang@...el.com>, <zgf574564920@...il.com>,
<linux-damon@...zon.com>, Linux MM <linux-mm@...ck.org>,
<linux-doc@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v23 07/15] mm/damon: Implement a debugfs-based user space interface
On Mon, 1 Feb 2021 09:37:39 -0800 Shakeel Butt <shakeelb@...gle.com> wrote:
> On Tue, Dec 15, 2020 at 3:59 AM SeongJae Park <sjpark@...zon.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.
>
> Which kernel space APIs are being referred here?
The symbols in 'include/linux/damon.h'
>
> > 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.
> >
[...]
> >
> > Signed-off-by: SeongJae Park <sjpark@...zon.de>
> > Reviewed-by: Leonard Foerster <foersleo@...zon.de>
> > ---
> > include/linux/damon.h | 3 +
> > mm/damon/Kconfig | 9 ++
> > mm/damon/Makefile | 1 +
> > mm/damon/core.c | 45 ++++++
> > mm/damon/dbgfs.c | 366 ++++++++++++++++++++++++++++++++++++++++++
> > 5 files changed, 424 insertions(+)
> > create mode 100644 mm/damon/dbgfs.c
> >
> > diff --git a/include/linux/damon.h b/include/linux/damon.h
> > index 39b4d6d3ddee..f9e0d4349352 100644
> > --- a/include/linux/damon.h
> > +++ b/include/linux/damon.h
> > @@ -265,9 +265,12 @@ unsigned int damon_nr_regions(struct damon_target *t);
> >
> > struct damon_ctx *damon_new_ctx(enum damon_target_type type);
> > void damon_destroy_ctx(struct damon_ctx *ctx);
> > +int damon_set_targets(struct damon_ctx *ctx,
> > + unsigned long *ids, ssize_t nr_ids);
> > int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
> > unsigned long aggr_int, unsigned long regions_update_int,
> > unsigned long min_nr_reg, unsigned long max_nr_reg);
> > +int damon_nr_running_ctxs(void);
> >
> > int damon_start(struct damon_ctx **ctxs, int nr_ctxs);
> > int damon_stop(struct damon_ctx **ctxs, int nr_ctxs);
> > diff --git a/mm/damon/Kconfig b/mm/damon/Kconfig
> > index 8ae080c52950..72f1683ba0ee 100644
> > --- a/mm/damon/Kconfig
> > +++ b/mm/damon/Kconfig
> > @@ -21,4 +21,13 @@ config DAMON_VADDR
> > This builds the default data access monitoring primitives for DAMON
> > that works for virtual address spaces.
> >
> > +config DAMON_DBGFS
> > + bool "DAMON debugfs interface"
> > + depends on DAMON_VADDR && DEBUG_FS
> > + help
> > + This builds the debugfs interface for DAMON. The user space admins
> > + can use the interface for arbitrary data access monitoring.
> > +
> > + If unsure, say N.
> > +
> > endmenu
> > diff --git a/mm/damon/Makefile b/mm/damon/Makefile
> > index 6ebbd08aed67..fed4be3bace3 100644
> > --- a/mm/damon/Makefile
> > +++ b/mm/damon/Makefile
> > @@ -2,3 +2,4 @@
> >
> > obj-$(CONFIG_DAMON) := core.o
> > obj-$(CONFIG_DAMON_VADDR) += vaddr.o
> > +obj-$(CONFIG_DAMON_DBGFS) += dbgfs.o
> > diff --git a/mm/damon/core.c b/mm/damon/core.c
> > index 5ca9f79ccbb6..b9575a6bebff 100644
> > --- a/mm/damon/core.c
> > +++ b/mm/damon/core.c
> > @@ -166,6 +166,37 @@ void damon_destroy_ctx(struct damon_ctx *ctx)
> > kfree(ctx);
> > }
> >
> > +/**
> > + * damon_set_targets() - Set monitoring targets.
> > + * @ctx: monitoring context
> > + * @ids: array of target ids
> > + * @nr_ids: number of entries in @ids
> > + *
> > + * This function should not be called while the kdamond is running.
> > + *
> > + * Return: 0 on success, negative error code otherwise.
> > + */
> > +int damon_set_targets(struct damon_ctx *ctx,
> > + unsigned long *ids, ssize_t nr_ids)
> > +{
> > + ssize_t i;
> > + struct damon_target *t, *next;
> > +
> > + damon_for_each_target_safe(t, next, ctx)
> > + damon_destroy_target(t);
>
> You need to put the reference on the target before destroying.
Oops, you're right. I will fix this in the next version.
>
> > +
> > + for (i = 0; i < nr_ids; i++) {
> > + t = damon_new_target(ids[i]);
> > + if (!t) {
> > + pr_err("Failed to alloc damon_target\n");
> > + return -ENOMEM;
> > + }
> > + damon_add_target(ctx, t);
> > + }
> > +
> > + return 0;
> > +}
> > +
> > /**
> > * damon_set_attrs() - Set attributes for the monitoring.
> > * @ctx: monitoring context
> > @@ -206,6 +237,20 @@ int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
> > return 0;
> > }
> >
> > +/**
> > + * damon_nr_running_ctxs() - Return number of currently running contexts.
> > + */
> > +int damon_nr_running_ctxs(void)
> > +{
> > + int nr_ctxs;
> > +
> > + mutex_lock(&damon_lock);
> > + nr_ctxs = nr_running_ctxs;
> > + mutex_unlock(&damon_lock);
>
> READ_ONCE(nr_running_ctxs) ?
I'd like to keep the code simpler to read, unless this turns out to be a real
performance bottleneck.
>
> > +
> > + return nr_ctxs;
> > +}
> > +
[...]
> > +
> > +static ssize_t dbgfs_target_ids_write(struct file *file,
> > + const char __user *buf, size_t count, loff_t *ppos)
> > +{
> > + struct damon_ctx *ctx = file->private_data;
> > + char *kbuf, *nrs;
> > + unsigned long *targets;
> > + ssize_t nr_targets;
> > + ssize_t ret = count;
> > + int i;
> > + int err;
> > +
> > + kbuf = user_input_str(buf, count, ppos);
> > + if (IS_ERR(kbuf))
> > + return PTR_ERR(kbuf);
> > +
> > + nrs = kbuf;
> > +
> > + targets = str_to_target_ids(nrs, ret, &nr_targets);
> > + if (!targets) {
> > + ret = -ENOMEM;
> > + goto out;
> > + }
> > +
> > + if (targetid_is_pid(ctx)) {
> > + for (i = 0; i < nr_targets; i++)
> > + targets[i] = (unsigned long)find_get_pid(
> > + (int)targets[i]);
> > + }
> > +
> > + mutex_lock(&ctx->kdamond_lock);
> > + if (ctx->kdamond) {
> > + ret = -EINVAL;
> > + goto unlock_out;
>
> You need to put_pid on the targets array.
Good catch!
>
> > + }
> > +
> > + err = damon_set_targets(ctx, targets, nr_targets);
> > + if (err)
> > + ret = err;
>
> You need to handle the partial failure from damon_set_targets().
My intention is to keep partial success as is.
>
>
> > +unlock_out:
> > + mutex_unlock(&ctx->kdamond_lock);
> > + kfree(targets);
> > +out:
> > + kfree(kbuf);
> > + return ret;
> > +}
[...]
Thanks,
SeongJae Park
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