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;
unsigned int nr_accesses_bp;
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.
nr_accesses_bp
nr_accesses in basis point (0.01%) that updated for each sampling interval.
list
List head for siblings.
age
Age of this region.
Description
nr_accesses is reset to zero for every damon_attrs->aggr_interval
and be
increased for every damon_attrs->sample_interval
if an access to the region
during the last sampling interval is found. The update of this field should
not be done with direct access but with the helper function,
damon_update_region_access_rate()
.
nr_accesses_bp is another representation of nr_accesses in basis point
(1 in 10,000) that updated for every damon_attrs->sample_interval
in a
manner similar to moving sum. By the algorithm, this value becomes
nr_accesses * 10000 for every struct damon_attrs
->aggr_interval. This can
be used when the aggregation interval is too huge and therefore cannot wait
for it before getting the access monitoring results.
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_LRU_PRIO
Prioritize the region on its LRU lists.
DAMOS_LRU_DEPRIO
Deprioritize the region on its LRU lists.
DAMOS_STAT
Do nothing but count the stat.
NR_DAMOS_ACTIONS
Total number of DAMOS actions
Description
The support of each action is up to running struct damon_operations
.
enum DAMON_OPS_VADDR
and enum DAMON_OPS_FVADDR
supports all actions except
enum DAMOS_LRU_PRIO
and enum DAMOS_LRU_DEPRIO
. enum DAMON_OPS_PADDR
supports only enum DAMOS_PAGEOUT
, enum DAMOS_LRU_PRIO
, enum
DAMOS_LRU_DEPRIO
, and DAMOS_STAT
.
-
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;
unsigned long (*get_score)(void *arg);
void *get_score_arg;
};
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.
get_score
Feedback function for self-tuning quota.
get_score_arg
Parameter for get_score
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.
If get_score function pointer is set, DAMON calls it back with get_score_arg and get the return value of it for every reset_interval. Then, DAMON adjusts the effective quota using the return value as a feedback score to the current quota, using its internal feedback loop algorithm.
The feedback loop algorithem assumes the quota input and the feedback score output are in a positive proportional relationship, and the goal of the tuning is getting the feedback screo value of 10,000. If ms and/or sz are set together, those work as a hard limit quota. If neither ms nor sz are set, the mechanism starts from the quota of one byte.
-
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.
-
enum damos_filter_type¶
Type of memory for
struct damos_filter
Constants
DAMOS_FILTER_TYPE_ANON
Anonymous pages.
DAMOS_FILTER_TYPE_MEMCG
Specific memcg's pages.
DAMOS_FILTER_TYPE_ADDR
Address range.
DAMOS_FILTER_TYPE_TARGET
Data Access Monitoring target.
NR_DAMOS_FILTER_TYPES
Number of filter types.
Description
The anon pages type and memcg type filters are handled by underlying
struct damon_operations
as a part of scheme action trying, and therefore
accounted as 'tried'. In contrast, other types are handled by core layer
before trying of the action and therefore not accounted as 'tried'.
The support of the filters that handled by struct damon_operations
depend
on the running struct damon_operations
.
enum DAMON_OPS_PADDR
supports both anon pages type and memcg type filters,
while enum DAMON_OPS_VADDR
and enum DAMON_OPS_FVADDR
don't support any of
the two types.
-
struct damos_filter¶
DAMOS action target memory filter.
Definition:
struct damos_filter {
enum damos_filter_type type;
bool matching;
union {
unsigned short memcg_id;
struct damon_addr_range addr_range;
int target_idx;
};
struct list_head list;
};
Members
type
Type of the page.
matching
If the matching page should filtered out or in.
{unnamed_union}
anonymous
memcg_id
Memcg id of the question if type is DAMOS_FILTER_MEMCG.
addr_range
Address range if type is DAMOS_FILTER_TYPE_ADDR.
target_idx
Index of the
struct damon_target
ofdamon_ctx->adaptive_targets
if type is DAMOS_FILTER_TYPE_TARGET.list
List head for siblings.
Description
Before applying the damos->action
to a memory region, DAMOS checks if each
page of the region matches to this and avoid applying the action if so.
Support of each filter type depends on the running struct damon_operations
and the type. Refer to enum damos_filter_type
for more detai.
-
struct damos_access_pattern¶
Target access pattern of the given scheme.
Definition:
struct damos_access_pattern {
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;
};
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.
-
struct damos¶
Represents a Data Access Monitoring-based Operation Scheme.
Definition:
struct damos {
struct damos_access_pattern pattern;
enum damos_action action;
unsigned long apply_interval_us;
struct damos_quota quota;
struct damos_watermarks wmarks;
struct list_head filters;
struct damos_stat stat;
struct list_head list;
};
Members
pattern
Access pattern of target regions.
action
damo_action
to be applied to the target regions.apply_interval_us
The time between applying the action.
quota
Control the aggressiveness of this scheme.
wmarks
Watermarks for automated (in)activation of this scheme.
filters
Additional set of
struct damos_filter
foraction
.stat
Statistics of this scheme.
list
List head for siblings.
Description
For each apply_interval_us, DAMON finds regions which fit in the
pattern
and applies action
to those. To avoid consuming too much
CPU time or IO resources for the action
, quota
is used.
If apply_interval_us is zero, damon_attrs->aggr_interval
is used instead.
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.
Before applying the action
to a memory region, struct damon_operations
implementation could check pages of the region and skip action
to respect
filters
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)(struct damon_target *t);
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_attrs.ops_update_interval
, and
check_accesses, target_valid and prepare_access_checks after each
damon_attrs.sample_interval
. Finally, reset_aggregated is called after
each damon_attrs.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);
int (*before_damos_apply)(struct damon_ctx *context,struct damon_target *target,struct damon_region *region, struct damos *scheme);
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_damos_apply
Called before applying DAMOS action.
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_attrs¶
Monitoring attributes for accuracy/overhead control.
Definition:
struct damon_attrs {
unsigned long sample_interval;
unsigned long aggr_interval;
unsigned long ops_update_interval;
unsigned long min_nr_regions;
unsigned long max_nr_regions;
};
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.
min_nr_regions
The minimum number of adaptive monitoring regions.
max_nr_regions
The maximum number of adaptive monitoring regions.
Description
For each sample_interval, DAMON checks whether each region is accessed or
not during the last sample_interval. If such access is found, DAMON
aggregates the information by increasing damon_region->nr_accesses
for
aggr_interval time. For each aggr_interval, the count is reset. 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.
-
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 {
struct damon_attrs attrs;
struct task_struct *kdamond;
struct mutex kdamond_lock;
struct damon_operations ops;
struct damon_callback callback;
struct list_head adaptive_targets;
struct list_head schemes;
};
Members
attrs
Monitoring attributes for accuracy/overhead control.
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.
adaptive_targets
Head of monitoring targets (
damon_target
) list.schemes
Head of schemes (
damos
) list.
Description
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 calling damon_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 from outside of the monitoring thread must
be protected by kdamond_lock.
Note that the monitoring thread protects only kdamond 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, struct damon_attrs *attrs)¶
Set attributes for the monitoring.
Parameters
struct damon_ctx *ctx
monitoring context
struct damon_attrs *attrs
monitoring attributes
Description
This function should be called while the kdamond is not running, or an
access check results aggregation is not ongoing (e.g., from
struct damon_callback
->after_aggregation or
struct damon_callback
->after_wmarks_check callbacks).
Every time interval is in micro-seconds.
Return
0 on success, negative error code otherwise.
-
void 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.
-
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.
-
int damon_set_region_biggest_system_ram_default(struct damon_target *t, unsigned long *start, unsigned long *end)¶
Set the region of the given monitoring target as requested, or biggest 'System RAM'.
Parameters
struct damon_target *t
The monitoring target to set the region.
unsigned long *start
The pointer to the start address of the region.
unsigned long *end
The pointer to the end address of the region.
Description
This function sets the region of t as requested by start and end. If the values of start and end are zero, however, this function finds the biggest 'System RAM' resource and sets the region to cover the resource. In the latter case, this function saves the start and end addresses of the resource in start and end, respectively.
Return
0 on success, negative error code otherwise.
-
void damon_update_region_access_rate(struct damon_region *r, bool accessed, struct damon_attrs *attrs)¶
Update the access rate of a region.
Parameters
struct damon_region *r
The DAMON region to update for its access check result.
bool accessed
Whether the region has accessed during last sampling interval.
struct damon_attrs *attrs
The damon_attrs of the DAMON context.
Description
Update the access rate of a region with the region's last sampling interval access check result.
Usually this will be called by damon_operations->check_accesses
callback.