mm/damon/core: set damos_filter default allowance behavior based on installed filters

Decide whether to allow or reject by default on core and opertions layer
handled filters evaluation stages.  It is decided as the opposite of the
last installed filter's behavior.  If there is no filter at all, allow by
default.  If there is any operations layer handled filters, core layer's
filtering stage sets allowing as the default behavior regardless of the
last filter of core layer-handling ones, since the last filter of core
layer handled filters in the case is not really the last filter of the
entire filtering stage.

Also, make the core layer's DAMOS filters handling stage uses the newly
set behavior field.

[sj@kernel.org: setup damos->{core,ops}_filters_default_reject for initial start]
Link: https://lkml.kernel.org/r/20250315222610.35245-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20250304211913.53574-8-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 3fbc31d..511c464 100644 (file)
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -518,7 +518,7 @@ struct damon_ctx *damon_new_ctx(void)
        ctx->attrs.ops_update_interval = 60 * 1000 * 1000;
 
        ctx->passed_sample_intervals = 0;
-       /* These will be set from kdamond_init_intervals_sis() */
+       /* These will be set from kdamond_init_ctx() */
        ctx->next_aggregation_sis = 0;
        ctx->next_ops_update_sis = 0;
 
@@ -891,6 +891,32 @@ static int damos_commit_ops_filters(struct damos *dst, struct damos *src)
        return 0;
 }
 
+/**
+ * damos_filters_default_reject() - decide whether to reject memory that didn't
+ *                                 match with any given filter.
+ * @filters:   Given DAMOS filters of a group.
+ */
+static bool damos_filters_default_reject(struct list_head *filters)
+{
+       struct damos_filter *last_filter;
+
+       if (list_empty(filters))
+               return false;
+       last_filter = list_last_entry(filters, struct damos_filter, list);
+       return last_filter->allow;
+}
+
+static void damos_set_filters_default_reject(struct damos *s)
+{
+       if (!list_empty(&s->ops_filters))
+               s->core_filters_default_reject = false;
+       else
+               s->core_filters_default_reject =
+                       damos_filters_default_reject(&s->filters);
+       s->ops_filters_default_reject =
+               damos_filters_default_reject(&s->ops_filters);
+}
+
 static int damos_commit_filters(struct damos *dst, struct damos *src)
 {
        int err;
@@ -898,7 +924,11 @@ static int damos_commit_filters(struct damos *dst, struct damos *src)
        err = damos_commit_core_filters(dst, src);
        if (err)
                return err;
-       return damos_commit_ops_filters(dst, src);
+       err = damos_commit_ops_filters(dst, src);
+       if (err)
+               return err;
+       damos_set_filters_default_reject(dst);
+       return 0;
 }
 
 static struct damos *damon_nth_scheme(int n, struct damon_ctx *ctx)
@@ -1580,7 +1610,7 @@ static bool damos_filter_out(struct damon_ctx *ctx, struct damon_target *t,
                        return !filter->allow;
                }
        }
-       return false;
+       return s->core_filters_default_reject;
 }
 
 /*
@@ -2315,7 +2345,7 @@ static int kdamond_wait_activation(struct damon_ctx *ctx)
        return -EBUSY;
 }
 
-static void kdamond_init_intervals_sis(struct damon_ctx *ctx)
+static void kdamond_init_ctx(struct damon_ctx *ctx)
 {
        unsigned long sample_interval = ctx->attrs.sample_interval ?
                ctx->attrs.sample_interval : 1;
@@ -2333,6 +2363,7 @@ static void kdamond_init_intervals_sis(struct damon_ctx *ctx)
                apply_interval = scheme->apply_interval_us ?
                        scheme->apply_interval_us : ctx->attrs.aggr_interval;
                scheme->next_apply_sis = apply_interval / sample_interval;
+               damos_set_filters_default_reject(scheme);
        }
 }
 
@@ -2350,7 +2381,7 @@ static int kdamond_fn(void *data)
        pr_debug("kdamond (%d) starts\n", current->pid);
 
        complete(&ctx->kdamond_started);
-       kdamond_init_intervals_sis(ctx);
+       kdamond_init_ctx(ctx);
 
        if (ctx->ops.init)
                ctx->ops.init(ctx);