Date:   Tue, 9 Jun 2020 10:47:45 +0200
From:   David Hildenbrand <david@...hat.com>
To:     SeongJae Park <sjpark@...zon.com>, akpm@...ux-foundation.org
Cc:     SeongJae Park <sjpark@...zon.de>, Jonathan.Cameron@...wei.com,
        aarcange@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, amit@...nel.org,
        benh@...nel.crashing.org, brendan.d.gregg@...il.com,
        brendanhiggins@...gle.com, cai@....pw, colin.king@...onical.com,
        corbet@....net, dwmw@...zon.com, foersleo@...zon.de,
        irogers@...gle.com, jolsa@...hat.com, kirill@...temov.name,
        mark.rutland@....com, mgorman@...e.de, minchan@...nel.org,
        mingo@...hat.com, namhyung@...nel.org, peterz@...radead.org,
        rdunlap@...radead.org, riel@...riel.com, rientjes@...gle.com,
        rostedt@...dmis.org, sblbir@...zon.com, shakeelb@...gle.com,
        shuah@...nel.org, sj38.park@...il.com, snu@...zon.de,
        vbabka@...e.cz, vdavydov.dev@...il.com, yang.shi@...ux.alibaba.com,
        ying.huang@...el.com, linux-damon@...zon.com, linux-mm@...ck.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC v11 3/8] mm/damon: Implement data access monitoring-based
 operation schemes

On 09.06.20 08:53, SeongJae Park wrote:
> From: SeongJae Park <sjpark@...zon.de>
> 
> In many cases, users might use DAMON for simple data access aware
> memory management optimizations such as applying an operation scheme to
> a memory region of a specific size having a specific access frequency
> for a specific time.  For example, "page out a memory region larger than
> 100 MiB but having a low access frequency more than 10 minutes", or "Use
> THP for a memory region larger than 2 MiB having a high access frequency
> for more than 2 seconds".
> 
> To minimize users from spending their time for implementation of such
> simple data access monitoring-based operation schemes, this commit makes
> DAMON to handle such schemes directly.  With this commit, users can
> simply specify their desired schemes to DAMON.

What would be the alternative? How would a solution where these policies
are handled by user space (or inside an application?) look like?

> 
> Each of the schemes is composed with conditions for filtering of the
> target memory regions and desired memory management action for the
> target.  Specifically, the format is::
> 
>     <min/max size> <min/max access frequency> <min/max age> <action>
> 
> The filtering conditions are size of memory region, number of accesses
> to the region monitored by DAMON, and the age of the region.  The age of
> region is incremented periodically but reset when its addresses or
> access frequency has significantly changed or the action of a scheme was
> applied.  For the action, current implementation supports only a few of
> madvise() hints, ``MADV_WILLNEED``, ``MADV_COLD``, ``MADV_PAGEOUT``,
> ``MADV_HUGEPAGE``, and ``MADV_NOHUGEPAGE``.

I am missing some important information. Is this specified for *all*
user space processes? Or how is this configured? What are examples?

E.g., messing with ``MADV_HUGEPAGE`` vs. ``MADV_NOHUGEPAGE`` of random
applications can change the behavior/break these applications. (e.g., if
userfaultfd is getting used and the applciation explicitly sets
MADV_NOHUGEPAGE).

> 
> Signed-off-by: SeongJae Park <sjpark@...zon.de>
> ---
>  include/linux/damon.h |  50 ++++++++++++++
>  mm/damon.c            | 149 ++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 199 insertions(+)
> 
> diff --git a/include/linux/damon.h b/include/linux/damon.h
> index 6a8ff2c63c2a..842a01e80c6e 100644
> --- a/include/linux/damon.h
> +++ b/include/linux/damon.h
> @@ -55,6 +55,52 @@ struct damon_task {
>  	struct list_head list;
>  };
>  
> +/**
> + * enum damos_action - Represents an action of a Data Access Monitoring-based
> + * Operation Scheme.
> + *
> + * @DAMOS_WILLNEED:	Call ``madvise()`` for the region with MADV_WILLNEED.
> + * @DAMOS_COLD:		Call ``madvise()`` for the region with MADV_COLD.
> + * @DAMOS_PAGEOUT:	Call ``madvise()`` for the region with MADV_PAGEOUT.
> + * @DAMOS_HUGEPAGE:	Call ``madvise()`` for the region with MADV_HUGEPAGE.
> + * @DAMOS_NOHUGEPAGE:	Call ``madvise()`` for the region with MADV_NOHUGEPAGE.
> + * @DAMOS_ACTION_LEN:	Number of supported actions.
> + */
> +enum damos_action {
> +	DAMOS_WILLNEED,
> +	DAMOS_COLD,
> +	DAMOS_PAGEOUT,
> +	DAMOS_HUGEPAGE,
> +	DAMOS_NOHUGEPAGE,
> +	DAMOS_ACTION_LEN,
> +};
> +
> +/**
> + * struct damos - Represents a Data Access Monitoring-based Operation Scheme.
> + * @min_sz_region:	Minimum size of target regions.
> + * @max_sz_region:	Maximum size of target regions.
> + * @min_nr_accesses:	Minimum ``->nr_accesses`` of target regions.
> + * @max_nr_accesses:	Maximum ``->nr_accesses`` of target regions.
> + * @min_age_region:	Minimum age of target regions.
> + * @max_age_region:	Maximum age of target regions.
> + * @action:		&damo_action to be applied to the target regions.
> + * @list:		List head for siblings.
> + *
> + * For each aggregation interval, DAMON applies @action to monitoring target
> + * regions fit in the condition and updates the statistics.  Note that both
> + * the minimums and the maximums are inclusive.
> + */
> +struct damos {
> +	unsigned int min_sz_region;
> +	unsigned int max_sz_region;
> +	unsigned int min_nr_accesses;
> +	unsigned int max_nr_accesses;
> +	unsigned int min_age_region;
> +	unsigned int max_age_region;
> +	enum damos_action action;
> +	struct list_head list;
> +};
> +
>  /**
>   * struct damon_ctx - Represents a context for each monitoring.  This is the
>   * main interface that allows users to set the attributes and get the results
> @@ -98,6 +144,7 @@ struct damon_task {
>   * @kdamond_lock.  Accesses to other fields must be protected by themselves.
>   *
>   * @tasks_list:		Head of monitoring target tasks (&damon_task) list.
> + * @schemes_list:	Head of schemes (&damos) list.
>   *
>   * @sample_cb:			Called for each sampling interval.
>   * @aggregate_cb:		Called for each aggregation interval.
> @@ -128,6 +175,7 @@ struct damon_ctx {
>  	struct mutex kdamond_lock;
>  
>  	struct list_head tasks_list;	/* 'damon_task' objects */
> +	struct list_head schemes_list;	/* 'damos' objects */
>  
>  	/* callbacks */
>  	void (*sample_cb)(struct damon_ctx *context);
> @@ -138,6 +186,8 @@ int damon_set_pids(struct damon_ctx *ctx, int *pids, ssize_t nr_pids);
>  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_set_schemes(struct damon_ctx *ctx,
> +			struct damos **schemes, ssize_t nr_schemes);
>  int damon_set_recording(struct damon_ctx *ctx,
>  				unsigned int rbuf_len, char *rfile_path);
>  int damon_start(struct damon_ctx *ctx);
> diff --git a/mm/damon.c b/mm/damon.c
> index 17ec5fcc1b96..1ec6fa3dd671 100644
> --- a/mm/damon.c
> +++ b/mm/damon.c
> @@ -22,6 +22,7 @@
>  
>  #define CREATE_TRACE_POINTS
>  
> +#include <asm-generic/mman-common.h>
>  #include <linux/damon.h>
>  #include <linux/debugfs.h>
>  #include <linux/delay.h>
> @@ -67,6 +68,12 @@
>  #define damon_for_each_task_safe(t, next, ctx) \
>  	list_for_each_entry_safe(t, next, &(ctx)->tasks_list, list)
>  
> +#define damon_for_each_scheme(s, ctx) \
> +	list_for_each_entry(s, &(ctx)->schemes_list, list)
> +
> +#define damon_for_each_scheme_safe(s, next, ctx) \
> +	list_for_each_entry_safe(s, next, &(ctx)->schemes_list, list)
> +
>  #define MAX_RECORD_BUFFER_LEN	(4 * 1024 * 1024)
>  #define MAX_RFILE_PATH_LEN	256
>  
> @@ -181,6 +188,27 @@ static void damon_destroy_task(struct damon_task *t)
>  	damon_free_task(t);
>  }
>  
> +static void damon_add_scheme(struct damon_ctx *ctx, struct damos *s)
> +{
> +	list_add_tail(&s->list, &ctx->schemes_list);
> +}
> +
> +static void damon_del_scheme(struct damos *s)
> +{
> +	list_del(&s->list);
> +}
> +
> +static void damon_free_scheme(struct damos *s)
> +{
> +	kfree(s);
> +}
> +
> +static void damon_destroy_scheme(struct damos *s)
> +{
> +	damon_del_scheme(s);
> +	damon_free_scheme(s);
> +}
> +
>  static unsigned int nr_damon_tasks(struct damon_ctx *ctx)
>  {
>  	struct damon_task *t;
> @@ -779,6 +807,101 @@ static void kdamond_reset_aggregated(struct damon_ctx *c)
>  	}
>  }
>  
> +#ifndef CONFIG_ADVISE_SYSCALLS
> +static int damos_madvise(struct damon_task *task, struct damon_region *r,
> +			int behavior)
> +{
> +	return -EINVAL;
> +}
> +#else
> +static int damos_madvise(struct damon_task *task, struct damon_region *r,
> +			int behavior)
> +{
> +	struct task_struct *t;
> +	struct mm_struct *mm;
> +	int ret = -ENOMEM;
> +
> +	t = damon_get_task_struct(task);
> +	if (!t)
> +		goto out;
> +	mm = damon_get_mm(task);
> +	if (!mm)
> +		goto put_task_out;
> +
> +	ret = do_madvise(t, mm, PAGE_ALIGN(r->vm_start),
> +			PAGE_ALIGN(r->vm_end - r->vm_start), behavior);
> +	mmput(mm);
> +put_task_out:
> +	put_task_struct(t);
> +out:
> +	return ret;
> +}
> +#endif	/* CONFIG_ADVISE_SYSCALLS */
> +
> +static int damos_do_action(struct damon_task *task, struct damon_region *r,
> +			enum damos_action action)
> +{
> +	int madv_action;
> +
> +	switch (action) {
> +	case DAMOS_WILLNEED:
> +		madv_action = MADV_WILLNEED;
> +		break;
> +	case DAMOS_COLD:
> +		madv_action = MADV_COLD;
> +		break;
> +	case DAMOS_PAGEOUT:
> +		madv_action = MADV_PAGEOUT;
> +		break;
> +	case DAMOS_HUGEPAGE:
> +		madv_action = MADV_HUGEPAGE;
> +		break;
> +	case DAMOS_NOHUGEPAGE:
> +		madv_action = MADV_NOHUGEPAGE;
> +		break;
> +	default:
> +		pr_warn("Wrong action %d\n", action);
> +		return -EINVAL;
> +	}
> +
> +	return damos_madvise(task, r, madv_action);
> +}
> +
> +static void damon_do_apply_schemes(struct damon_ctx *c, struct damon_task *t,
> +				struct damon_region *r)
> +{
> +	struct damos *s;
> +	unsigned long sz;
> +
> +	damon_for_each_scheme(s, c) {
> +		sz = r->vm_end - r->vm_start;
> +		if ((s->min_sz_region && sz < s->min_sz_region) ||
> +				(s->max_sz_region && s->max_sz_region < sz))
> +			continue;
> +		if ((s->min_nr_accesses && r->nr_accesses < s->min_nr_accesses)
> +				|| (s->max_nr_accesses &&
> +					s->max_nr_accesses < r->nr_accesses))
> +			continue;
> +		if ((s->min_age_region && r->age < s->min_age_region) ||
> +				(s->max_age_region &&
> +				 s->max_age_region < r->age))
> +			continue;
> +		damos_do_action(t, r, s->action);
> +		r->age = 0;
> +	}
> +}
> +
> +static void kdamond_apply_schemes(struct damon_ctx *c)
> +{
> +	struct damon_task *t;
> +	struct damon_region *r;
> +
> +	damon_for_each_task(t, c) {
> +		damon_for_each_region(r, t)
> +			damon_do_apply_schemes(c, t, r);
> +	}
> +}
> +
>  #define sz_damon_region(r) (r->vm_end - r->vm_start)
>  
>  /*
> @@ -1001,6 +1124,7 @@ static int kdamond_fn(void *data)
>  			kdamond_merge_regions(ctx, max_nr_accesses / 10);
>  			if (ctx->aggregate_cb)
>  				ctx->aggregate_cb(ctx);
> +			kdamond_apply_schemes(ctx);
>  			kdamond_reset_aggregated(ctx);
>  			kdamond_split_regions(ctx);
>  		}
> @@ -1081,6 +1205,30 @@ int damon_stop(struct damon_ctx *ctx)
>  	return -EPERM;
>  }
>  
> +/**
> + * damon_set_schemes() - Set data access monitoring based operation schemes.
> + * @ctx:	monitoring context
> + * @schemes:	array of the schemes
> + * @nr_schemes:	number of entries in @schemes
> + *
> + * This function should not be called while the kdamond of the context is
> + * running.
> + *
> + * Return: 0 if success, or negative error code otherwise.
> + */
> +int damon_set_schemes(struct damon_ctx *ctx, struct damos **schemes,
> +			ssize_t nr_schemes)
> +{
> +	struct damos *s, *next;
> +	ssize_t i;
> +
> +	damon_for_each_scheme_safe(s, next, ctx)
> +		damon_destroy_scheme(s);
> +	for (i = 0; i < nr_schemes; i++)
> +		damon_add_scheme(ctx, schemes[i]);
> +	return 0;
> +}
> +
>  /**
>   * damon_set_pids() - Set monitoring target processes.
>   * @ctx:	monitoring context
> @@ -1525,6 +1673,7 @@ static int __init damon_init_user_ctx(void)
>  	mutex_init(&ctx->kdamond_lock);
>  
>  	INIT_LIST_HEAD(&ctx->tasks_list);
> +	INIT_LIST_HEAD(&ctx->schemes_list);
>  
>  	return 0;
>  }
> 


-- 
Thanks,

David / dhildenb

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