API Reference

Kernel space programs can use every feature of DAMON using below APIs. All you need to do is including damon.h, which is located in include/linux/ of the source tree.

Structures

struct damon_addr_range

Represents an address region of [start, end).

Definition

struct damon_addr_range {
  unsigned long start;
  unsigned long end;
};

Members

start

Start address of the region (inclusive).

end

End address of the region (exclusive).

struct damon_region

Represents a monitoring target region.

Definition

struct damon_region {
  struct damon_addr_range ar;
  unsigned long sampling_addr;
  unsigned int nr_accesses;
  struct list_head list;
  unsigned int age;
};

Members

ar

The address range of the region.

sampling_addr

Address of the sample for the next access check.

nr_accesses

Access frequency of this region.

list

List head for siblings.

age

Age of this region.

Description

age is initially zero, increased for each aggregation interval, and reset to zero again if the access frequency is significantly changed. If two regions are merged into a new region, both nr_accesses and age of the new region are set as region size-weighted average of those of the two regions.

struct damon_target

Represents a monitoring target.

Definition

struct damon_target {
  struct pid *pid;
  unsigned int nr_regions;
  struct list_head regions_list;
  struct list_head list;
};

Members

pid

The PID of the virtual address space to monitor.

nr_regions

Number of monitoring target regions of this target.

regions_list

Head of the monitoring target regions of this target.

list

List head for siblings.

Description

Each monitoring context could have multiple targets. For example, a context for virtual memory address spaces could have multiple target processes. The pid should be set for appropriate struct damon_operations including the virtual address spaces monitoring operations.

enum damos_action

Represents an action of a Data Access Monitoring-based Operation Scheme.

Constants

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_STAT

Do nothing but count the stat.

NR_DAMOS_ACTIONS

Total number of DAMOS actions

struct damos_quota

Controls the aggressiveness of the given scheme.

Definition

struct damos_quota {
  unsigned long ms;
  unsigned long sz;
  unsigned long reset_interval;
  unsigned int weight_sz;
  unsigned int weight_nr_accesses;
  unsigned int weight_age;
};

Members

ms

Maximum milliseconds that the scheme can use.

sz

Maximum bytes of memory that the action can be applied.

reset_interval

Charge reset interval in milliseconds.

weight_sz

Weight of the region’s size for prioritization.

weight_nr_accesses

Weight of the region’s nr_accesses for prioritization.

weight_age

Weight of the region’s age for prioritization.

Description

To avoid consuming too much CPU time or IO resources for applying the struct damos->action to large memory, DAMON allows users to set time and/or size quotas. The quotas can be set by writing non-zero values to ms and sz, respectively. If the time quota is set, DAMON tries to use only up to ms milliseconds within reset_interval for applying the action. If the size quota is set, DAMON tries to apply the action only up to sz bytes within reset_interval.

Internally, the time quota is transformed to a size quota using estimated throughput of the scheme’s action. DAMON then compares it against sz and uses smaller one as the effective quota.

For selecting regions within the quota, DAMON prioritizes current scheme’s target memory regions using the struct damon_operations->get_scheme_score. You could customize the prioritization logic by setting weight_sz, weight_nr_accesses, and weight_age, because monitoring operations are encouraged to respect those.

enum damos_wmark_metric

Represents the watermark metric.

Constants

DAMOS_WMARK_NONE

Ignore the watermarks of the given scheme.

DAMOS_WMARK_FREE_MEM_RATE

Free memory rate of the system in [0,1000].

NR_DAMOS_WMARK_METRICS

Total number of DAMOS watermark metrics

struct damos_watermarks

Controls when a given scheme should be activated.

Definition

struct damos_watermarks {
  enum damos_wmark_metric metric;
  unsigned long interval;
  unsigned long high;
  unsigned long mid;
  unsigned long low;
};

Members

metric

Metric for the watermarks.

interval

Watermarks check time interval in microseconds.

high

High watermark.

mid

Middle watermark.

low

Low watermark.

Description

If metric is DAMOS_WMARK_NONE, the scheme is always active. Being active means DAMON does monitoring and applying the action of the scheme to appropriate memory regions. Else, DAMON checks metric of the system for at least every interval microseconds and works as below.

If metric is higher than high, the scheme is inactivated. If metric is between mid and low, the scheme is activated. If metric is lower than low, the scheme is inactivated.

struct damos_stat

Statistics on a given scheme.

Definition

struct damos_stat {
  unsigned long nr_tried;
  unsigned long sz_tried;
  unsigned long nr_applied;
  unsigned long sz_applied;
  unsigned long qt_exceeds;
};

Members

nr_tried

Total number of regions that the scheme is tried to be applied.

sz_tried

Total size of regions that the scheme is tried to be applied.

nr_applied

Total number of regions that the scheme is applied.

sz_applied

Total size of regions that the scheme is applied.

qt_exceeds

Total number of times the quota of the scheme has exceeded.

struct damos

Represents a Data Access Monitoring-based Operation Scheme.

Definition

struct damos {
  unsigned long min_sz_region;
  unsigned long 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 damos_quota quota;
  struct damos_watermarks wmarks;
  struct damos_stat stat;
  struct list_head list;
};

Members

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.

quota

Control the aggressiveness of this scheme.

wmarks

Watermarks for automated (in)activation of this scheme.

stat

Statistics of this scheme.

list

List head for siblings.

Description

For each aggregation interval, DAMON finds regions which fit in the condition (min_sz_region, max_sz_region, min_nr_accesses, max_nr_accesses, min_age_region, max_age_region) and applies action to those. To avoid consuming too much CPU time or IO resources for the action, quota is used.

To do the work only when needed, schemes can be activated for specific system situations using wmarks. If all schemes that registered to the monitoring context are inactive, DAMON stops monitoring either, and just repeatedly checks the watermarks.

If all schemes that registered to a struct damon_ctx are inactive, DAMON stops monitoring and just repeatedly checks the watermarks.

After applying the action to each region, stat_count and stat_sz is updated to reflect the number of regions and total size of regions that the action is applied.

enum damon_ops_id

Identifier for each monitoring operations implementation

Constants

DAMON_OPS_VADDR

Monitoring operations for virtual address spaces

DAMON_OPS_FVADDR

Monitoring operations for only fixed ranges of virtual address spaces

DAMON_OPS_PADDR

Monitoring operations for the physical address space

NR_DAMON_OPS

Number of monitoring operations implementations

struct damon_operations

Monitoring operations for given use cases.

Definition

struct damon_operations {
  enum damon_ops_id id;
  void (*init)(struct damon_ctx *context);
  void (*update)(struct damon_ctx *context);
  void (*prepare_access_checks)(struct damon_ctx *context);
  unsigned int (*check_accesses)(struct damon_ctx *context);
  void (*reset_aggregated)(struct damon_ctx *context);
  int (*get_scheme_score)(struct damon_ctx *context,struct damon_target *t, struct damon_region *r, struct damos *scheme);
  unsigned long (*apply_scheme)(struct damon_ctx *context,struct damon_target *t, struct damon_region *r, struct damos *scheme);
  bool (*target_valid)(void *target);
  void (*cleanup)(struct damon_ctx *context);
};

Members

id

Identifier of this operations set.

init

Initialize operations-related data structures.

update

Update operations-related data structures.

prepare_access_checks

Prepare next access check of target regions.

check_accesses

Check the accesses to target regions.

reset_aggregated

Reset aggregated accesses monitoring results.

get_scheme_score

Get the score of a region for a scheme.

apply_scheme

Apply a DAMON-based operation scheme.

target_valid

Determine if the target is valid.

cleanup

Clean up the context.

Description

DAMON can be extended for various address spaces and usages. For this, users should register the low level operations for their target address space and usecase via the damon_ctx.ops. Then, the monitoring thread (damon_ctx.kdamond) calls init and prepare_access_checks before starting the monitoring, update after each damon_ctx.ops_update_interval, and check_accesses, target_valid and prepare_access_checks after each damon_ctx.sample_interval. Finally, reset_aggregated is called after each damon_ctx.aggr_interval.

Each struct damon_operations instance having valid id can be registered via damon_register_ops() and selected by damon_select_ops() later. init should initialize operations-related data structures. For example, this could be used to construct proper monitoring target regions and link those to damon_ctx.adaptive_targets. update should update the operations-related data structures. For example, this could be used to update monitoring target regions for current status. prepare_access_checks should manipulate the monitoring regions to be prepared for the next access check. check_accesses should check the accesses to each region that made after the last preparation and update the number of observed accesses of each region. It should also return max number of observed accesses that made as a result of its update. The value will be used for regions adjustment threshold. reset_aggregated should reset the access monitoring results that aggregated by check_accesses. get_scheme_score should return the priority score of a region for a scheme as an integer in [0, DAMOS_MAX_SCORE]. apply_scheme is called from kdamond when a region for user provided DAMON-based operation scheme is found. It should apply the scheme’s action to the region and return bytes of the region that the action is successfully applied. target_valid should check whether the target is still valid for the monitoring. cleanup is called from kdamond just before its termination.

struct damon_callback

Monitoring events notification callbacks.

Definition

struct damon_callback {
  void *private;
  int (*before_start)(struct damon_ctx *context);
  int (*after_wmarks_check)(struct damon_ctx *context);
  int (*after_sampling)(struct damon_ctx *context);
  int (*after_aggregation)(struct damon_ctx *context);
  void (*before_terminate)(struct damon_ctx *context);
};

Members

private

User private data.

before_start

Called before starting the monitoring.

after_wmarks_check

Called after each schemes’ watermarks check.

after_sampling

Called after each sampling.

after_aggregation

Called after each aggregation.

before_terminate

Called before terminating the monitoring.

Description

The monitoring thread (damon_ctx.kdamond) calls before_start and before_terminate just before starting and finishing the monitoring, respectively. Therefore, those are good places for installing and cleaning private.

The monitoring thread calls after_wmarks_check after each DAMON-based operation schemes’ watermarks check. If users need to make changes to the attributes of the monitoring context while it’s deactivated due to the watermarks, this is the good place to do.

The monitoring thread calls after_sampling and after_aggregation for each of the sampling intervals and aggregation intervals, respectively. Therefore, users can safely access the monitoring results without additional protection. For the reason, users are recommended to use these callback for the accesses to the results.

If any callback returns non-zero, monitoring stops.

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 of the monitoring.

Definition

struct damon_ctx {
  unsigned long sample_interval;
  unsigned long aggr_interval;
  unsigned long ops_update_interval;
  struct task_struct *kdamond;
  struct mutex kdamond_lock;
  struct damon_operations ops;
  struct damon_callback callback;
  unsigned long min_nr_regions;
  unsigned long max_nr_regions;
  struct list_head adaptive_targets;
  struct list_head schemes;
};

Members

sample_interval

The time between access samplings.

aggr_interval

The time between monitor results aggregations.

ops_update_interval

The time between monitoring operations updates.

kdamond

Kernel thread who does the monitoring.

kdamond_lock

Mutex for the synchronizations with kdamond.

ops

Set of monitoring operations for given use cases.

callback

Set of callbacks for monitoring events notifications.

min_nr_regions

The minimum number of adaptive monitoring regions.

max_nr_regions

The maximum number of adaptive monitoring regions.

adaptive_targets

Head of monitoring targets (damon_target) list.

schemes

Head of schemes (damos) list.

Description

For each sample_interval, DAMON checks whether each region is accessed or not. It aggregates and keeps the access information (number of accesses to each region) for aggr_interval time. DAMON also checks whether the target memory regions need update (e.g., by mmap() calls from the application, in case of virtual memory monitoring) and applies the changes for each ops_update_interval. All time intervals are in micro-seconds. Please refer to struct damon_operations and struct damon_callback for more detail.

For each monitoring context, one kernel thread for the monitoring is created. The pointer to the thread is stored in kdamond.

Once started, the monitoring thread runs until explicitly required to be terminated or every monitoring target is invalid. The validity of the targets is checked via the damon_operations.target_valid of ops. The termination can also be explicitly requested by writing non-zero to kdamond_stop. The thread sets kdamond to NULL when it terminates. Therefore, users can know whether the monitoring is ongoing or terminated by reading kdamond. Reads and writes to kdamond and kdamond_stop from outside of the monitoring thread must be protected by kdamond_lock.

Note that the monitoring thread protects only kdamond and kdamond_stop via kdamond_lock. Accesses to other fields must be protected by themselves.

Functions

bool damon_is_registered_ops(enum damon_ops_id id)

Check if a given damon_operations is registered.

Parameters

enum damon_ops_id id

Id of the damon_operations to check if registered.

Return

true if the ops is set, false otherwise.

int damon_register_ops(struct damon_operations *ops)

Register a monitoring operations set to DAMON.

Parameters

struct damon_operations *ops

monitoring operations set to register.

Description

This function registers a monitoring operations set of valid struct damon_operations->id so that others can find and use them later.

Return

0 on success, negative error code otherwise.

int damon_select_ops(struct damon_ctx *ctx, enum damon_ops_id id)

Select a monitoring operations to use with the context.

Parameters

struct damon_ctx *ctx

monitoring context to use the operations.

enum damon_ops_id id

id of the registered monitoring operations to select.

Description

This function finds registered monitoring operations set of id and make ctx to use it.

Return

0 on success, negative error code otherwise.

int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int, unsigned long aggr_int, unsigned long ops_upd_int, unsigned long min_nr_reg, unsigned long max_nr_reg)

Set attributes for the monitoring.

Parameters

struct damon_ctx *ctx

monitoring context

unsigned long sample_int

time interval between samplings

unsigned long aggr_int

time interval between aggregations

unsigned long ops_upd_int

time interval between monitoring operations updates

unsigned long min_nr_reg

minimal number of regions

unsigned long max_nr_reg

maximum number of regions

Description

This function should not be called while the kdamond is running. Every time interval is in micro-seconds.

Return

0 on success, negative error code otherwise.

int damon_set_schemes(struct damon_ctx *ctx, struct damos **schemes, ssize_t nr_schemes)

Set data access monitoring based operation schemes.

Parameters

struct damon_ctx *ctx

monitoring context

struct damos **schemes

array of the schemes

ssize_t nr_schemes

number of entries in schemes

Description

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_nr_running_ctxs(void)

Return number of currently running contexts.

Parameters

void

no arguments

int damon_start(struct damon_ctx **ctxs, int nr_ctxs, bool exclusive)

Starts the monitorings for a given group of contexts.

Parameters

struct damon_ctx **ctxs

an array of the pointers for contexts to start monitoring

int nr_ctxs

size of ctxs

bool exclusive

exclusiveness of this contexts group

Description

This function starts a group of monitoring threads for a group of monitoring contexts. One thread per each context is created and run in parallel. The caller should handle synchronization between the threads by itself. If exclusive is true and a group of threads that created by other ‘damon_start()’ call is currently running, this function does nothing but returns -EBUSY.

Return

0 on success, negative error code otherwise.

int damon_stop(struct damon_ctx **ctxs, int nr_ctxs)

Stops the monitorings for a given group of contexts.

Parameters

struct damon_ctx **ctxs

an array of the pointers for contexts to stop monitoring

int nr_ctxs

size of ctxs

Return

0 on success, negative error code otherwise.