[RFC PATCH 0/7] mm/damon/reclaim,lru_sort: monitor all system rams by default

[RFC PATCH 0/7] mm/damon/reclaim,lru_sort: monitor all system rams by default

[SeongJae Park]

DAMON_RECLAIM and DAMON_LRU_SORT set the biggest 'System RAM' resource
of the system as the default monitoring target address range.  The main
intention behind the design is to minimize the overhead coming from
monitoring of non-System RAM areas.

This could result in an odd setup when there are multiple discrete
System RAMs of considerable sizes.  For example, there are System RAMs
each having 500 GiB size.  In this case, only the first 500 GiB will be
set as the monitoring region by default.  This is particularly common on
NUMA systems.  Hence the modules allow users to set the monitoring
target address range using the module parameters if the default setup
doesn't work for them.  In other words, the current design trades ease
of setup for lower overhead.

However, because DAMON utilizes the sampling based access check and the
adaptive regions adjustment mechanisms, the overhead from the monitoring
of non-System RAM areas should be negligible in most setups.  Meanwhile,
the setup complexity is causing real headaches for users who need to run
those modules on various types of systems.  That is, the current
tradeoff is not a good deal.

Set the physical address range that can cover all System RAM areas of
the system as the default monitoring regions for DAMON_RECLAIM and
DAMON_LRU_SORT.

Technically speaking, this is changing documented behavior.  However, it
makes no sense to believe there is a real use case that really depends
on the old weird default behavior.  If the old default behavior was
working for them in the reasonable way, this change will only add a
negligible amount of monitoring overhead.  If it didn't work, the users
may already be using manual monitoring regions setup, and they will not
be affected by this change.

Patches Sequence
================

Patch 1 introduces a new core function that will be used for the new
default monitoring target region setup.  Patch 2 and 3 update
DAMON_RECLAIM and DAMON_LRU_SORT to use the new function instead of the
old one, respectively.  Patch 4 removes the old core function that was
replaced by the new one, as there is no more user of it.  Patch 5
updates DAMON_STAT to use the new one instead of its in-house
nearly-duplicate self implementation of the functionality.  Finally
patches 6 and 7 update the DAMON_RECLAIM and DAMON_LRU_SORT user
documentation for the new behaviors, respectively.

SeongJae Park (7):
  mm/damon: introduce damon_set_region_system_rams_default()
  mm/damon/reclaim: cover all system rams
  mm/damon/lru_sort: cover all system rams
  mm/damon/core: remove damon_set_region_biggest_system_ram_default()
  mm/damon/stat: use damon_set_region_system_rams_default()
  Docs/admin-guide/mm/damon/reclaim: update for entire memory monitoring
  Docs/admin-guide/mm/damon/lru_sort: update for entire memory
    monitoring

 .../admin-guide/mm/damon/lru_sort.rst         |  6 ++-
 .../admin-guide/mm/damon/reclaim.rst          |  6 ++-
 include/linux/damon.h                         |  2 +-
 mm/damon/core.c                               | 49 +++++++++--------
 mm/damon/lru_sort.c                           |  8 +--
 mm/damon/reclaim.c                            | 14 ++---
 mm/damon/stat.c                               | 53 ++-----------------
 7 files changed, 50 insertions(+), 88 deletions(-)


base-commit: 11bcd10460e9446785fc04deb5d175806a00400b
-- 
2.47.3

[RFC PATCH 1/7] mm/damon: introduce damon_set_region_system_rams_default()

[SeongJae Park]

damon_set_region_biggest_system_ram_default() sets the monitoring target
region as the caller requested.  If the caller didn't specify the
region, it finds the biggest System RAM of the system and sets it as the
target region.  When there are more than one considerable size of System
RAM resources in the system, the default target setup makes no sense.
Introduce a variant, namely damon_set_region_system_rams_default().  It
sets a physical address range that covers all System RAM resources as
the default target region.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h |  5 +++
 mm/damon/core.c       | 77 ++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 77 insertions(+), 5 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 5fb1dc585658b..c4cdaa01ea530 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -1007,6 +1007,11 @@ int damon_kdamond_pid(struct damon_ctx *ctx);
 int damon_call(struct damon_ctx *ctx, struct damon_call_control *control);
 int damos_walk(struct damon_ctx *ctx, struct damos_walk_control *control);
 
+int damon_set_region_system_rams_default(struct damon_target *t,
+				unsigned long *start, unsigned long *end,
+				unsigned long addr_unit,
+				unsigned long min_region_sz);
+
 int damon_set_region_biggest_system_ram_default(struct damon_target *t,
 				unsigned long *start, unsigned long *end,
 				unsigned long addr_unit,
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 48633da449104..3cef74ba7f0f4 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -3186,14 +3186,20 @@ static int kdamond_fn(void *data)
 	return 0;
 }
 
-static int walk_system_ram(struct resource *res, void *arg)
+struct damon_system_ram_range_walk_arg {
+	bool walked;
+	struct resource res;
+};
+
+static int damon_system_ram_walk_fn(struct resource *res, void *arg)
 {
-	struct resource *a = arg;
+	struct damon_system_ram_range_walk_arg *a = arg;
 
-	if (resource_size(a) < resource_size(res)) {
-		a->start = res->start;
-		a->end = res->end;
+	if (!a->walked) {
+		a->walked = true;
+		a->res.start = res->start;
 	}
+	a->res.end = res->end;
 	return 0;
 }
 
@@ -3210,6 +3216,67 @@ static unsigned long damon_res_to_core_addr(resource_size_t ra,
 	return ra / addr_unit;
 }
 
+static bool damon_find_system_rams_range(unsigned long *start,
+		unsigned long *end, unsigned long addr_unit)
+{
+	struct damon_system_ram_range_walk_arg arg = {};
+
+	walk_system_ram_res(0, -1, &arg, damon_system_ram_walk_fn);
+	if (!arg.walked)
+		return false;
+	*start = damon_res_to_core_addr(arg.res.start, addr_unit);
+	*end = damon_res_to_core_addr(arg.res.end + 1, addr_unit);
+	if (*end <= *start)
+		return false;
+	return true;
+}
+
+/**
+ * damon_set_region_system_rams_default() - Set the region of the given
+ * monitoring target as requested, or to cover all 'System RAM' resources.
+ * @t:		The monitoring target to set the region.
+ * @start:	The pointer to the start address of the region.
+ * @end:	The pointer to the end address of the region.
+ * @addr_unit:	The address unit for the damon_ctx of @t.
+ * @min_region_sz:	Minimum region size.
+ *
+ * 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 'System
+ * RAM' resources and sets the region to cover all the resource.  In the latter
+ * case, this function saves the start and the end addresseses of the first and
+ * the last resources in @start and @end, respectively.
+ *
+ * Return: 0 on success, negative error code otherwise.
+ */
+int damon_set_region_system_rams_default(struct damon_target *t,
+			unsigned long *start, unsigned long *end,
+			unsigned long addr_unit, unsigned long min_region_sz)
+{
+	struct damon_addr_range addr_range;
+
+	if (*start > *end)
+		return -EINVAL;
+
+	if (!*start && !*end &&
+		!damon_find_system_rams_range(start, end, addr_unit))
+		return -EINVAL;
+
+	addr_range.start = *start;
+	addr_range.end = *end;
+	return damon_set_regions(t, &addr_range, 1, min_region_sz);
+}
+
+static int walk_system_ram(struct resource *res, void *arg)
+{
+	struct resource *a = arg;
+
+	if (resource_size(a) < resource_size(res)) {
+		a->start = res->start;
+		a->end = res->end;
+	}
+	return 0;
+}
+
 /*
  * Find biggest 'System RAM' resource and store its start and end address in
  * @start and @end, respectively.  If no System RAM is found, returns false.
-- 
2.47.3

[RFC PATCH 2/7] mm/damon/reclaim: cover all system rams

[SeongJae Park]

DAMON_RECLAIM allows users to set the physical address range to monitor
and do the work on.  When users don't explicitly set the range, the
biggest System RAM resource of the system is selected as the monitoring
target address range.  The intention was to reduce the overhead from
monitoring non-System RAM areas because monitoring of non-System RAM may
be meaningless.  However, because of the sampling based access check and
adaptive regions adjustment, the overhead should be negligible.  It
makes more sense to just cover all system rams of the system.  Do so.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/reclaim.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/mm/damon/reclaim.c b/mm/damon/reclaim.c
index 89998d28628c4..ecfc6b58d07d2 100644
--- a/mm/damon/reclaim.c
+++ b/mm/damon/reclaim.c
@@ -127,7 +127,8 @@ DEFINE_DAMON_MODULES_MON_ATTRS_PARAMS(damon_reclaim_mon_attrs);
  * Start of the target memory region in physical address.
  *
  * The start physical address of memory region that DAMON_RECLAIM will do work
- * against.  By default, biggest System RAM is used as the region.
+ * against.  By default, the system's entire physical memory is used as the
+ * region.
  */
 static unsigned long monitor_region_start __read_mostly;
 module_param(monitor_region_start, ulong, 0600);
@@ -136,7 +137,8 @@ module_param(monitor_region_start, ulong, 0600);
  * End of the target memory region in physical address.
  *
  * The end physical address of memory region that DAMON_RECLAIM will do work
- * against.  By default, biggest System RAM is used as the region.
+ * against.  By default, the system's entire physical memory is used as the
+ * region.
  */
 static unsigned long monitor_region_end __read_mostly;
 module_param(monitor_region_end, ulong, 0600);
@@ -264,11 +266,9 @@ static int damon_reclaim_apply_parameters(void)
 		damos_add_filter(scheme, filter);
 	}
 
-	err = damon_set_region_biggest_system_ram_default(param_target,
-					&monitor_region_start,
-					&monitor_region_end,
-					param_ctx->addr_unit,
-					param_ctx->min_region_sz);
+	err = damon_set_region_system_rams_default(param_target,
+			&monitor_region_start, &monitor_region_end,
+			param_ctx->addr_unit, param_ctx->min_region_sz);
 	if (err)
 		goto out;
 	err = damon_commit_ctx(ctx, param_ctx);
-- 
2.47.3

[RFC PATCH 3/7] mm/damon/lru_sort: cover all system rams

[SeongJae Park]

DAMON_LRU_SORT allows users to set the physical address range to monitor
and do the work on.  When users don't explicitly set the range, the
biggest system ram resource of the system is selected as the monitoring
target address range.  The intention was to reduce the overhead from
monitoring non-System RAM areas because monitoring non-System RAM may be
meaningless.  However, because of the sampling based access check and
adaptive regions adjustment, the overhead should be negligible.  It
makes more sense to just cover all system rams of the system.  Do so.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/lru_sort.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/damon/lru_sort.c b/mm/damon/lru_sort.c
index 641af42cc2d1a..48ddfa6369c93 100644
--- a/mm/damon/lru_sort.c
+++ b/mm/damon/lru_sort.c
@@ -139,7 +139,8 @@ DEFINE_DAMON_MODULES_MON_ATTRS_PARAMS(damon_lru_sort_mon_attrs);
  * Start of the target memory region in physical address.
  *
  * The start physical address of memory region that DAMON_LRU_SORT will do work
- * against.  By default, biggest System RAM is used as the region.
+ * against.  By default, the system's entire phyiscal memory is used as the
+ * region.
  */
 static unsigned long monitor_region_start __read_mostly;
 module_param(monitor_region_start, ulong, 0600);
@@ -148,7 +149,8 @@ module_param(monitor_region_start, ulong, 0600);
  * End of the target memory region in physical address.
  *
  * The end physical address of memory region that DAMON_LRU_SORT will do work
- * against.  By default, biggest System RAM is used as the region.
+ * against.  By default, the system's entire phyiscal memory is used as the
+ * region.
  */
 static unsigned long monitor_region_end __read_mostly;
 module_param(monitor_region_end, ulong, 0600);
@@ -335,7 +337,7 @@ static int damon_lru_sort_apply_parameters(void)
 	if (err)
 		goto out;
 
-	err = damon_set_region_biggest_system_ram_default(param_target,
+	err = damon_set_region_system_rams_default(param_target,
 					&monitor_region_start,
 					&monitor_region_end,
 					param_ctx->addr_unit,
-- 
2.47.3

[RFC PATCH 4/7] mm/damon/core: remove damon_set_region_biggest_system_ram_default()

[SeongJae Park]

Now nobody is using damon_set_region_biggest_system_ram_default().
Remove it.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h |  5 ----
 mm/damon/core.c       | 64 -------------------------------------------
 2 files changed, 69 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index c4cdaa01ea530..1a4f754ad89be 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -1012,11 +1012,6 @@ int damon_set_region_system_rams_default(struct damon_target *t,
 				unsigned long addr_unit,
 				unsigned long min_region_sz);
 
-int damon_set_region_biggest_system_ram_default(struct damon_target *t,
-				unsigned long *start, unsigned long *end,
-				unsigned long addr_unit,
-				unsigned long min_region_sz);
-
 #endif	/* CONFIG_DAMON */
 
 #endif	/* _DAMON_H */
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 3cef74ba7f0f4..d2c8c088e7451 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -3266,70 +3266,6 @@ int damon_set_region_system_rams_default(struct damon_target *t,
 	return damon_set_regions(t, &addr_range, 1, min_region_sz);
 }
 
-static int walk_system_ram(struct resource *res, void *arg)
-{
-	struct resource *a = arg;
-
-	if (resource_size(a) < resource_size(res)) {
-		a->start = res->start;
-		a->end = res->end;
-	}
-	return 0;
-}
-
-/*
- * Find biggest 'System RAM' resource and store its start and end address in
- * @start and @end, respectively.  If no System RAM is found, returns false.
- */
-static bool damon_find_biggest_system_ram(unsigned long *start,
-		unsigned long *end, unsigned long addr_unit)
-
-{
-	struct resource res = {};
-
-	walk_system_ram_res(0, -1, &res, walk_system_ram);
-	*start = damon_res_to_core_addr(res.start, addr_unit);
-	*end = damon_res_to_core_addr(res.end + 1, addr_unit);
-	if (*end <= *start)
-		return false;
-	return true;
-}
-
-/**
- * damon_set_region_biggest_system_ram_default() - Set the region of the given
- * monitoring target as requested, or biggest 'System RAM'.
- * @t:		The monitoring target to set the region.
- * @start:	The pointer to the start address of the region.
- * @end:	The pointer to the end address of the region.
- * @addr_unit:	The address unit for the damon_ctx of @t.
- * @min_region_sz:	Minimum region size.
- *
- * 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.
- */
-int damon_set_region_biggest_system_ram_default(struct damon_target *t,
-			unsigned long *start, unsigned long *end,
-			unsigned long addr_unit, unsigned long min_region_sz)
-{
-	struct damon_addr_range addr_range;
-
-	if (*start > *end)
-		return -EINVAL;
-
-	if (!*start && !*end &&
-			!damon_find_biggest_system_ram(start, end, addr_unit))
-		return -EINVAL;
-
-	addr_range.start = *start;
-	addr_range.end = *end;
-	return damon_set_regions(t, &addr_range, 1, min_region_sz);
-}
-
 /*
  * damon_moving_sum() - Calculate an inferred moving sum value.
  * @mvsum:	Inferred sum of the last @len_window values.
-- 
2.47.3

[RFC PATCH 5/7] mm/damon/stat: use damon_set_region_system_rams_default()

[SeongJae Park]

damon_stat_set_moniotirng_region() is nearly a duplicate of the core
function, damon_set_region_system_rams_default().  Use the core
implementation.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/stat.c | 53 +++----------------------------------------------
 1 file changed, 3 insertions(+), 50 deletions(-)

diff --git a/mm/damon/stat.c b/mm/damon/stat.c
index 4901e9a7c3398..da2ebf90ef64e 100644
--- a/mm/damon/stat.c
+++ b/mm/damon/stat.c
@@ -154,59 +154,12 @@ static int damon_stat_damon_call_fn(void *data)
 	return 0;
 }
 
-struct damon_stat_system_ram_range_walk_arg {
-	bool walked;
-	struct resource res;
-};
-
-static int damon_stat_system_ram_walk_fn(struct resource *res, void *arg)
-{
-	struct damon_stat_system_ram_range_walk_arg *a = arg;
-
-	if (!a->walked) {
-		a->walked = true;
-		a->res.start = res->start;
-	}
-	a->res.end = res->end;
-	return 0;
-}
-
-static unsigned long damon_stat_res_to_core_addr(resource_size_t ra,
-		unsigned long addr_unit)
-{
-	/*
-	 * Use div_u64() for avoiding linking errors related with __udivdi3,
-	 * __aeabi_uldivmod, or similar problems.  This should also improve the
-	 * performance optimization (read div_u64() comment for the detail).
-	 */
-	if (sizeof(ra) == 8 && sizeof(addr_unit) == 4)
-		return div_u64(ra, addr_unit);
-	return ra / addr_unit;
-}
-
-static int damon_stat_set_monitoring_region(struct damon_target *t,
-		unsigned long addr_unit, unsigned long min_region_sz)
-{
-	struct damon_addr_range addr_range;
-	struct damon_stat_system_ram_range_walk_arg arg = {};
-
-	walk_system_ram_res(0, -1, &arg, damon_stat_system_ram_walk_fn);
-	if (!arg.walked)
-		return -EINVAL;
-	addr_range.start = damon_stat_res_to_core_addr(
-			arg.res.start, addr_unit);
-	addr_range.end = damon_stat_res_to_core_addr(
-			arg.res.end + 1, addr_unit);
-	if (addr_range.end <= addr_range.start)
-		return -EINVAL;
-	return damon_set_regions(t, &addr_range, 1, min_region_sz);
-}
-
 static struct damon_ctx *damon_stat_build_ctx(void)
 {
 	struct damon_ctx *ctx;
 	struct damon_attrs attrs;
 	struct damon_target *target;
+	unsigned long start = 0, end = 0;
 
 	ctx = damon_new_ctx();
 	if (!ctx)
@@ -236,8 +189,8 @@ static struct damon_ctx *damon_stat_build_ctx(void)
 	if (!target)
 		goto free_out;
 	damon_add_target(ctx, target);
-	if (damon_stat_set_monitoring_region(target, ctx->addr_unit,
-				ctx->min_region_sz))
+	if (damon_set_region_system_rams_default(target, &start, &end,
+				ctx->addr_unit, ctx->min_region_sz))
 		goto free_out;
 	return ctx;
 free_out:
-- 
2.47.3

[RFC PATCH 6/7] Docs/admin-guide/mm/damon/reclaim: update for entire memory monitoring

[SeongJae Park]

Update DAMON_RECLAIM usage document for the changed default monitoring
target region selection.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 Documentation/admin-guide/mm/damon/reclaim.rst | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/mm/damon/reclaim.rst b/Documentation/admin-guide/mm/damon/reclaim.rst
index b14a065586271..ec7e3e32b4ac6 100644
--- a/Documentation/admin-guide/mm/damon/reclaim.rst
+++ b/Documentation/admin-guide/mm/damon/reclaim.rst
@@ -240,7 +240,8 @@ Start of target memory region in physical address.
 
 The start physical address of memory region that DAMON_RECLAIM will do work
 against.  That is, DAMON_RECLAIM will find cold memory regions in this region
-and reclaims.  By default, biggest System RAM is used as the region.
+and reclaims.  By default, the system's entire physical memory is used as the
+region.
 
 monitor_region_end
 ------------------
@@ -249,7 +250,8 @@ End of target memory region in physical address.
 
 The end physical address of memory region that DAMON_RECLAIM will do work
 against.  That is, DAMON_RECLAIM will find cold memory regions in this region
-and reclaims.  By default, biggest System RAM is used as the region.
+and reclaims.  By default, the system's entire physical memory is used as the
+region.
 
 addr_unit
 ---------
-- 
2.47.3

[RFC PATCH 7/7] Docs/admin-guide/mm/damon/lru_sort: update for entire memory monitoring

[SeongJae Park]

Update DAMON_LRU_SORT usage document for the changed default monitoring
target region selection.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 Documentation/admin-guide/mm/damon/lru_sort.rst | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/mm/damon/lru_sort.rst b/Documentation/admin-guide/mm/damon/lru_sort.rst
index 25e2f042a383f..796b0a028555d 100644
--- a/Documentation/admin-guide/mm/damon/lru_sort.rst
+++ b/Documentation/admin-guide/mm/damon/lru_sort.rst
@@ -246,7 +246,8 @@ monitor_region_start
 Start of target memory region in physical address.
 
 The start physical address of memory region that DAMON_LRU_SORT will do work
-against.  By default, biggest System RAM is used as the region.
+against.  By default, the system's entire phyiscal memory is used as the
+region.
 
 monitor_region_end
 ------------------
@@ -254,7 +255,8 @@ monitor_region_end
 End of target memory region in physical address.
 
 The end physical address of memory region that DAMON_LRU_SORT will do work
-against.  By default, biggest System RAM is used as the region.
+against.  By default, the system's entire physical memory is used as the
+region.
 
 addr_unit
 ---------
-- 
2.47.3