Re: [RFC PATCH v4 2/4] mm/damon: introduce DAMON_HUGEPAGE for hot region hugepage collapsing

[Gutierrez Asier]

On 6/12/2026 3:46 AM, SeongJae Park wrote:
> On Thu, 11 Jun 2026 15:02:42 +0000 <gutierrez.asier@xxxxxxxxxxxxxxxxxxx> wrote:
> 
>> From: Asier Gutierrez <gutierrez.asier@xxxxxxxxxxxxxxxxxxx>
>>
>> This patch introduces a new DAMON module (SAMPLE_DAMON_HUGEPAGE)
>> which collapses hot regions into huge pages.
> 
> To the previous revision, I suggested SAMPLE_DAMON_HPAGE.  Because you didn't
> comment more, I thought my suggestion is accepted.  Can you please elaborate
> why you use this name instead of the suggested one?
> 
> If there is no special reason, could you please do 's/hugepage/hpage/a' for
> this patch?
I thought hugepage should be fine. I'll rename it.
>>
>> SAMPLE_DAMON_HUGEPAGE operates in the virtual memory space, for a
>> specific task. The user is expected to supply the PID of the task
>> that is going to be monitored through the monitored_pid module
>> variable.
>>
>> SAMPLE_DAMON_HUGEPAGE uses the hugepage auto-tune mechanism to
>> increase or decrease the aggressiveness of page collapsing. User
>> autotuning is also available for additional tuning aggressiveness
>> control.
>>
>> The module also includes changes to the DAMON compilation, so that
>> the module can be enabled or disabled.
> 
> The above sentence is wrong?
> 
>>
>> Signed-off-by: Asier Gutierrez <gutierrez.asier@xxxxxxxxxxxxxxxxxxx>
>> ---
>>  samples/damon/Kconfig          |  12 ++
>>  samples/damon/Makefile         |   1 +
>>  samples/damon/hugepage.c (new) | 207 +++++++++++++++++++++++++++++++++
>>  3 files changed, 220 insertions(+)
>>
>> diff --git a/samples/damon/Kconfig b/samples/damon/Kconfig
>> index cbf96fd8a8bf..512f150aaabb 100644
>> --- a/samples/damon/Kconfig
>> +++ b/samples/damon/Kconfig
>> @@ -40,4 +40,16 @@ config SAMPLE_DAMON_MTIER
>>  
>>  	  If unsure, say N.
>>  
>> +config SAMPLE_DAMON_HUGEPAGE
>> +	bool "Build DAMON-based collapse of hot regions (SAMPLE_DAMON_HUGEPAGE)"
>> +	depends on DAMON && DAMON_VADDR
>> +	help
>> +	  This module monitors a certain PID provided by the user through
>> +	  monitored_pid attribute. Hot regions are determined by DAMON-based
> 
> target_pid?
Right, I renamed the parameter in the module but not in the config. I'll change it.
>> +	  sampling. Collapsing occurs according to the quota goal using total
>> +	  memory usage to huge page usage ratio. The ratio is set by the user
>> +	  through a module attribute.
>> +
>> +	  If unsure, say N.
> 
> Please give a simple one sentence at the beginning of the help message, like
> other sample modules.
OK, I will do it.
>> +
>>  endmenu
>> diff --git a/samples/damon/Makefile b/samples/damon/Makefile
>> index 72f68cbf422a..96bde2c44846 100644
>> --- a/samples/damon/Makefile
>> +++ b/samples/damon/Makefile
>> @@ -3,3 +3,4 @@
>>  obj-$(CONFIG_SAMPLE_DAMON_WSSE) += wsse.o
>>  obj-$(CONFIG_SAMPLE_DAMON_PRCL) += prcl.o
>>  obj-$(CONFIG_SAMPLE_DAMON_MTIER) += mtier.o
>> +obj-$(CONFIG_SAMPLE_DAMON_HUGEPAGE)	+= hugepage.o
>> diff --git a/samples/damon/hugepage.c b/samples/damon/hugepage.c
>> new file mode 100644
>> index 000000000000..2c7fd213a8db
>> --- /dev/null
>> +++ b/samples/damon/hugepage.c
>> @@ -0,0 +1,207 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Copyright (C) 2026 HUAWEI, Inc.
>> + *             https://www.huawei.com
>> + *
>> + * Author: Asier Gutierrez <gutierrez.asier@xxxxxxxxxxxxxxxxxxx>
>> + */
>> +
>> +#define pr_fmt(fmt) "damon_sample_hugepage: " fmt
>> +
>> +#include <linux/damon.h>
>> +#include <linux/kstrtox.h>
>> +#include <linux/module.h>
>> +
>> +#ifdef MODULE_PARAM_PREFIX
>> +#undef MODULE_PARAM_PREFIX
>> +#endif
>> +#define MODULE_PARAM_PREFIX "damon_sample_hugepage."
>> +
>> +static bool enabled __read_mostly;
>> +
>> +static unsigned long target_pid;
>> +module_param(target_pid, ulong, 0600);
>> +
>> +/* By default, total huge pages to system memory usage ratio set to 10% */
>> +static unsigned long quota_percentage_hugepage __read_mostly = 1000;
>> +module_param(quota_percentage_hugepage, ulong, 0600);
>> +
>> +static unsigned long quota_autotune_feedback __read_mostly;
>> +module_param(quota_autotune_feedback, ulong, 0600);
>> +
>> +static struct damon_ctx *ctx;
>> +static struct pid *target_pidp;
>> +
>> +static int damon_sample_hugepage_damon_call_fn(void *data)
>> +{
>> +	struct damon_ctx *c = data;
>> +	struct damon_target *t;
>> +
>> +	damon_for_each_target(t, c) {
>> +		struct damon_region *r;
>> +		unsigned long hugepages = 0;
>> +
>> +		damon_for_each_region(r, t) {
>> +			if (r->nr_accesses > 0)
>> +				hugepages += r->ar.end - r->ar.start;
>> +		}
>> +		hugepages = hugepages / HPAGE_PMD_SIZE;
>> +		pr_info("hugepage: %lu\n", hugepages);
>> +	}
>> +	return 0;
>> +}
>> +
>> +static struct damon_call_control call_control = {
>> +	.fn = damon_sample_hugepage_damon_call_fn,
>> +	.repeat = true,
>> +};
>> +
>> +static int damon_sample_hugepage_start(void)
>> +{
>> +	int err;
>> +	struct damon_target *target;
>> +	struct damos *scheme;
>> +	struct damos_quota_goal *goal;
>> +
>> +	pr_info("start\n");
>> +
>> +
>> +	ctx = damon_new_ctx();
>> +	if (!ctx)
>> +		return -ENOMEM;
>> +	if (damon_select_ops(ctx, DAMON_OPS_VADDR)) {
>> +		damon_destroy_ctx(ctx);
>> +		return -EINVAL;
>> +	}
>> +
>> +	target = damon_new_target();
>> +	if (!target) {
>> +		damon_destroy_ctx(ctx);
>> +		return -ENOMEM;
>> +	}
>> +	damon_add_target(ctx, target);
>> +	target_pidp = find_get_pid(target_pid);
>> +	if (!target_pidp) {
>> +		damon_destroy_ctx(ctx);
>> +		return -EINVAL;
>> +	}
>> +	target->pid = target_pidp;
>> +
>> +	scheme = damon_new_scheme(&(struct damos_access_pattern) {
>> +				.min_sz_region = HPAGE_PMD_SIZE,
>> +				.max_sz_region = ULONG_MAX,
>> +				.min_nr_accesses = 0,
>> +				.max_nr_accesses = UINT_MAX,
>> +				.min_age_region = 50,
>> +				.max_age_region = UINT_MAX},
>> +				DAMOS_COLLAPSE, 0,
>> +				&(struct damos_quota) {
>> +				.ms = 10,
>> +				.sz = 128 * 1024 * 1024,
>> +				.reset_interval = 1000,
>> +				.weight_sz = 0,
>> +				.weight_nr_accesses = 1,
>> +				.weight_age = 1,
>> +				.goal_tuner = DAMOS_QUOTA_GOAL_TUNER_TEMPORAL},
>> +				&(struct damos_watermarks){}, NUMA_NO_NODE);
>> +	if (!scheme) {
>> +		damon_destroy_ctx(ctx);
>> +		return -ENOMEM;
>> +	}
>> +	damon_set_schemes(ctx, &scheme, 1);
>> +	goal = damos_new_quota_goal(DAMOS_QUOTA_HUGEPAGE_MEM_BP,
>> +				quota_percentage_hugepage);
>> +	if (!goal) {
>> +		damon_destroy_ctx(ctx);
>> +		return -ENOMEM;
>> +	}
>> +	damos_add_quota_goal(&scheme->quota, goal);
>> +
>> +	if (quota_autotune_feedback) {
>> +		goal = damos_new_quota_goal(DAMOS_QUOTA_USER_INPUT, 10000);
>> +		if (!goal) {
>> +			damon_destroy_ctx(ctx);
>> +			return -ENOMEM;
>> +		}
>> +		goal->current_value = quota_autotune_feedback;
>> +		damos_add_quota_goal(&scheme->quota, goal);
>> +	}
>> +
>> +	err = damon_start(&ctx, 1, true);
>> +	if (err) {
>> +		damon_destroy_ctx(ctx);
>> +		return err;
>> +	}
>> +
>> +	call_control.data = ctx;
>> +	err = damon_call(ctx, &call_control);
>> +	if (err) {
>> +		damon_stop(&ctx, 1);
>> +		damon_destroy_ctx(ctx);
>> +	}
>> +	return err;
>> +}
>> +
>> +static void damon_sample_hugepage_stop(void)
>> +{
>> +	pr_info("stop\n");
>> +	if (ctx) {
>> +		damon_stop(&ctx, 1);
>> +		damon_destroy_ctx(ctx);
>> +	}
>> +}
>> +static int damon_sample_hugepage_enabled_store(const char *val,
>> +				const struct kernel_param *kp)
>> +{
>> +	bool is_enabled = enabled;
>> +	int err;
>> +
>> +	err = kstrtobool(val, &enabled);
>> +	if (err)
>> +		return err;
>> +
>> +	if (enabled == is_enabled)
>> +		return 0;
>> +
>> +	if (!damon_initialized())
>> +		return 0;
>> +
>> +	if (enabled) {
>> +		err = damon_sample_hugepage_start();
>> +		if (err)
>> +			enabled = false;
>> +		return err;
>> +	}
>> +	damon_sample_hugepage_stop();
>> +	return 0;
>> +}
>> +
>> +static const struct kernel_param_ops enabled_param_ops = {
>> +	.set = damon_sample_hugepage_enabled_store,
>> +	.get = param_get_bool,
>> +};
>> +
>> +module_param_cb(enabled, &enabled_param_ops, &enabled, 0600);
>> +MODULE_PARM_DESC(enabled,
>> +	"Enable or disable DAMON_HUGEPAGE (default: disabled)");
>> +
>> +static int __init damon_sample_hugepage_init(void)
>> +{
>> +	int err = 0;
>> +
>> +	if (!damon_initialized()) {
>> +		if (enabled)
>> +			enabled = false;
>> +		pr_warn("Module not initialized\n");
>> +		return -ENOMEM;
>> +	}
>> +
>> +	if (enabled) {
>> +		err = damon_sample_hugepage_start();
>> +		if (err)
>> +			enabled = false;
>> +	}
>> +	return err;
>> +}
>> +
>> +module_init(damon_sample_hugepage_init);
>> -- 
>> 2.43.0
> 
> Looks good overall, except the name that is not consistent to other sample
> modules.
> 
> The wrong sentence in the commit message makes me feel this patch is not really
> ready for a review of details, though.  I therefore skipped reviewing each
> details.  Could you plese thoroughly check details in the next revision?  I
> will reiterate more details in the next revision, then.
OK
> 
> Thanks,
> SJ
> 

-- 
Asier Gutierrez
Huawei