[PATCH 01/11] mm/damon/core: split out DAMOS-charged region skip logic into a new function

SeongJae Park
2022-10-24T22:29:24Z

The DAMOS action applying function, 'damon_do_apply_schemes()', is quite
long and not so simple. Split out the already quota-charged region skip
code, which is not a small amount of simple code, into a new function
with some comments for better readability.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
mm/damon/core.c | 96 +++++++++++++++++++++++++++++++++----------------
1 file changed, 65 insertions(+), 31 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 36d098d06c55..06b50ede9cc6 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -694,6 +694,67 @@ static bool damos_valid_target(struct damon_ctx *c, struct damon_target *t,
return c->ops.get_scheme_score(c, t, r, s) >= s->quota.min_score;
}

+/*
+ * damos_skip_charged_region() - Check if the given region or starting part of
+ * it is already charged for the DAMOS quota.
+ * @t: The target of the region.
+ * @rp: The pointer to the region.
+ * @s: The scheme to be applied.
+ *
+ * If a quota of a scheme has exceeded in a quota charge window, the scheme's
+ * action would applied to only a part of the target access pattern fulfilling
+ * regions. To avoid applying the scheme action to only already applied
+ * regions, DAMON skips applying the scheme action to the regions that charged
+ * in the previous charge window.
+ *
+ * This function checks if a given region should be skipped or not for the
+ * reason. If only the starting part of the region has previously charged,
+ * this function splits the region into two so that the second one covers the
+ * area that not charged in the previous charge widnow and saves the second
+ * region in *rp and returns false, so that the caller can apply DAMON action
+ * to the second one.
+ *
+ * Return: true if the region should be entirely skipped, false otherwise.
+ */
+static bool damos_skip_charged_region(struct damon_target *t,
+ struct damon_region **rp, struct damos *s)
+{
+ struct damon_region *r = *rp;
+ struct damos_quota *quota = &s->quota;
+ unsigned long sz_to_skip;
+
+ /* Skip previously charged regions */
+ if (quota->charge_target_from) {
+ if (t != quota->charge_target_from)
+ return true;
+ if (r == damon_last_region(t)) {
+ quota->charge_target_from = NULL;
+ quota->charge_addr_from = 0;
+ return true;
+ }
+ if (quota->charge_addr_from &&
+ r->ar.end <= quota->charge_addr_from)
+ return true;
+
+ if (quota->charge_addr_from && r->ar.start <
+ quota->charge_addr_from) {
+ sz_to_skip = ALIGN_DOWN(quota->charge_addr_from -
+ r->ar.start, DAMON_MIN_REGION);
+ if (!sz_to_skip) {
+ if (damon_sz_region(r) <= DAMON_MIN_REGION)
+ return true;
+ sz_to_skip = DAMON_MIN_REGION;
+ }
+ damon_split_region_at(t, r, sz_to_skip);
+ r = damon_next_region(r);
+ *rp = r;
+ }
+ quota->charge_target_from = NULL;
+ quota->charge_addr_from = 0;
+ }
+ return false;
+}
+
static void damon_do_apply_schemes(struct damon_ctx *c,
struct damon_target *t,
struct damon_region *r)
@@ -702,7 +763,7 @@ static void damon_do_apply_schemes(struct damon_ctx *c,

damon_for_each_scheme(s, c) {
struct damos_quota *quota = &s->quota;
- unsigned long sz = damon_sz_region(r);
+ unsigned long sz;
struct timespec64 begin, end;
unsigned long sz_applied = 0;

@@ -713,41 +774,14 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
if (quota->esz && quota->charged_sz >= quota->esz)
continue;

- /* Skip previously charged regions */
- if (quota->charge_target_from) {
- if (t != quota->charge_target_from)
- continue;
- if (r == damon_last_region(t)) {
- quota->charge_target_from = NULL;
- quota->charge_addr_from = 0;
- continue;
- }
- if (quota->charge_addr_from &&
- r->ar.end <= quota->charge_addr_from)
- continue;
-
- if (quota->charge_addr_from && r->ar.start <
- quota->charge_addr_from) {
- sz = ALIGN_DOWN(quota->charge_addr_from -
- r->ar.start, DAMON_MIN_REGION);
- if (!sz) {
- if (damon_sz_region(r) <=
- DAMON_MIN_REGION)
- continue;
- sz = DAMON_MIN_REGION;
- }
- damon_split_region_at(t, r, sz);
- r = damon_next_region(r);
- sz = damon_sz_region(r);
- }
- quota->charge_target_from = NULL;
- quota->charge_addr_from = 0;
- }
+ if (damos_skip_charged_region(t, &r, s))
+ continue;

if (!damos_valid_target(c, t, r, s))
continue;

/* Apply the scheme */
+ sz = damon_sz_region(r);
if (c->ops.apply_scheme) {
if (quota->esz &&
quota->charged_sz + sz > quota->esz) {
--
2.25.1