[PATCH OLK-6.6 002/156] mm/damon/core: use number of passed access sampling as a timer

From: SeongJae Park sj@kernel.org

stable inclusion from stable-v6.6.9 commit c708a5e51b43797539d787f27ee947d95986c382 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I8SU2D

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...

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[ Upstream commit 4472edf63d6630e6cf65e205b4fc8c3c94d0afe5 ]

DAMON sleeps for sampling interval after each sampling, and check if the aggregation interval and the ops update interval have passed using ktime_get_coarse_ts64() and baseline timestamps for the intervals. That design is for making the operations occur at deterministic timing regardless of the time that spend for each work. However, it turned out it is not that useful, and incur not-that-intuitive results.

After all, timer functions, and especially sleep functions that DAMON uses to wait for specific timing, are not necessarily strictly accurate. It is legal design, so no problem. However, depending on such inaccuracies, the nr_accesses can be larger than aggregation interval divided by sampling interval. For example, with the default setting (5 ms sampling interval and 100 ms aggregation interval) we frequently show regions having nr_accesses larger than 20. Also, if the execution of a DAMOS scheme takes a long time, next aggregation could happen before enough number of samples are collected. This is not what usual users would intuitively expect.

Since access check sampling is the smallest unit work of DAMON, using the number of passed sampling intervals as the DAMON-internal timer can easily avoid these problems. That is, convert aggregation and ops update intervals to numbers of sampling intervals that need to be passed before those operations be executed, count the number of passed sampling intervals, and invoke the operations as soon as the specific amount of sampling intervals passed. Make the change.

Note that this could make a behavioral change to settings that using intervals that not aligned by the sampling interval. For example, if the sampling interval is 5 ms and the aggregation interval is 12 ms, DAMON effectively uses 15 ms as its aggregation interval, because it checks whether the aggregation interval after sleeping the sampling interval. This change will make DAMON to effectively use 10 ms as aggregation interval, since it uses 'aggregation interval / sampling interval * sampling interval' as the effective aggregation interval, and we don't use floating point types. Usual users would have used aligned intervals, so this behavioral change is not expected to make any meaningful impact, so just make this change.

Link: https://lkml.kernel.org/r/20230914021523.60649-1-sj@kernel.org Signed-off-by: SeongJae Park sj@kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Stable-dep-of: 6376a8245956 ("mm/damon/core: make damon_start() waits until kdamond_fn() starts") Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com --- include/linux/damon.h | 14 ++++++- mm/damon/core.c | 96 +++++++++++++++++++++---------------------- 2 files changed, 59 insertions(+), 51 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h index c70cca8a839f..506118916378 100644 --- a/include/linux/damon.h +++ b/include/linux/damon.h @@ -522,8 +522,18 @@ struct damon_ctx { struct damon_attrs attrs;

/* private: internal use only */ - struct timespec64 last_aggregation; - struct timespec64 last_ops_update; + /* number of sample intervals that passed since this context started */ + unsigned long passed_sample_intervals; + /* + * number of sample intervals that should be passed before next + * aggregation + */ + unsigned long next_aggregation_sis; + /* + * number of sample intervals that should be passed before next ops + * update + */ + unsigned long next_ops_update_sis;

/* public: */ struct task_struct *kdamond; diff --git a/mm/damon/core.c b/mm/damon/core.c index fd5be73f699f..30c93de59475 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -427,8 +427,10 @@ struct damon_ctx *damon_new_ctx(void) ctx->attrs.aggr_interval = 100 * 1000; ctx->attrs.ops_update_interval = 60 * 1000 * 1000;

- ktime_get_coarse_ts64(&ctx->last_aggregation); - ctx->last_ops_update = ctx->last_aggregation; + ctx->passed_sample_intervals = 0; + /* These will be set from kdamond_init_intervals_sis() */ + ctx->next_aggregation_sis = 0; + ctx->next_ops_update_sis = 0;

mutex_init(&ctx->kdamond_lock);

@@ -542,6 +544,9 @@ static void damon_update_monitoring_results(struct damon_ctx *ctx, */ int damon_set_attrs(struct damon_ctx *ctx, struct damon_attrs *attrs) { + unsigned long sample_interval = attrs->sample_interval ? + attrs->sample_interval : 1; + if (attrs->min_nr_regions < 3) return -EINVAL; if (attrs->min_nr_regions > attrs->max_nr_regions) @@ -549,6 +554,11 @@ int damon_set_attrs(struct damon_ctx *ctx, struct damon_attrs *attrs) if (attrs->sample_interval > attrs->aggr_interval) return -EINVAL;

+ ctx->next_aggregation_sis = ctx->passed_sample_intervals + + attrs->aggr_interval / sample_interval; + ctx->next_ops_update_sis = ctx->passed_sample_intervals + + attrs->ops_update_interval / sample_interval; + damon_update_monitoring_results(ctx, attrs); ctx->attrs = *attrs; return 0; @@ -722,38 +732,6 @@ int damon_stop(struct damon_ctx **ctxs, int nr_ctxs) return err; }

-/* - * damon_check_reset_time_interval() - Check if a time interval is elapsed. - * @baseline: the time to check whether the interval has elapsed since - * @interval: the time interval (microseconds) - * - * See whether the given time interval has passed since the given baseline - * time. If so, it also updates the baseline to current time for next check. - * - * Return: true if the time interval has passed, or false otherwise. - */ -static bool damon_check_reset_time_interval(struct timespec64 *baseline, - unsigned long interval) -{ - struct timespec64 now; - - ktime_get_coarse_ts64(&now); - if ((timespec64_to_ns(&now) - timespec64_to_ns(baseline)) < - interval * 1000) - return false; - *baseline = now; - return true; -} - -/* - * Check whether it is time to flush the aggregated information - */ -static bool kdamond_aggregate_interval_passed(struct damon_ctx *ctx) -{ - return damon_check_reset_time_interval(&ctx->last_aggregation, - ctx->attrs.aggr_interval); -} - /* * Reset the aggregated monitoring results ('nr_accesses' of each region). */ @@ -1234,18 +1212,6 @@ static void kdamond_split_regions(struct damon_ctx *ctx) last_nr_regions = nr_regions; }

-/* - * Check whether it is time to check and apply the operations-related data - * structures. - * - * Returns true if it is. - */ -static bool kdamond_need_update_operations(struct damon_ctx *ctx) -{ - return damon_check_reset_time_interval(&ctx->last_ops_update, - ctx->attrs.ops_update_interval); -} - /* * Check whether current monitoring should be stopped * @@ -1357,6 +1323,17 @@ static int kdamond_wait_activation(struct damon_ctx *ctx) return -EBUSY; }

+static void kdamond_init_intervals_sis(struct damon_ctx *ctx) +{ + unsigned long sample_interval = ctx->attrs.sample_interval ? + ctx->attrs.sample_interval : 1; + + ctx->passed_sample_intervals = 0; + ctx->next_aggregation_sis = ctx->attrs.aggr_interval / sample_interval; + ctx->next_ops_update_sis = ctx->attrs.ops_update_interval / + sample_interval; +} + /* * The monitoring daemon that runs as a kernel thread */ @@ -1370,6 +1347,8 @@ static int kdamond_fn(void *data)

pr_debug("kdamond (%d) starts\n", current->pid);

+ kdamond_init_intervals_sis(ctx); + if (ctx->ops.init) ctx->ops.init(ctx); if (ctx->callback.before_start && ctx->callback.before_start(ctx)) @@ -1378,6 +1357,17 @@ static int kdamond_fn(void *data) sz_limit = damon_region_sz_limit(ctx);

while (!kdamond_need_stop(ctx)) { + /* + * ctx->attrs and ctx->next_{aggregation,ops_update}_sis could + * be changed from after_wmarks_check() or after_aggregation() + * callbacks. Read the values here, and use those for this + * iteration. That is, damon_set_attrs() updated new values + * are respected from next iteration. + */ + unsigned long next_aggregation_sis = ctx->next_aggregation_sis; + unsigned long next_ops_update_sis = ctx->next_ops_update_sis; + unsigned long sample_interval = ctx->attrs.sample_interval; + if (kdamond_wait_activation(ctx)) break;

@@ -1387,12 +1377,17 @@ static int kdamond_fn(void *data) ctx->callback.after_sampling(ctx)) break;

- kdamond_usleep(ctx->attrs.sample_interval); + kdamond_usleep(sample_interval); + ctx->passed_sample_intervals++;

if (ctx->ops.check_accesses) max_nr_accesses = ctx->ops.check_accesses(ctx);

- if (kdamond_aggregate_interval_passed(ctx)) { + sample_interval = ctx->attrs.sample_interval ? + ctx->attrs.sample_interval : 1; + if (ctx->passed_sample_intervals == next_aggregation_sis) { + ctx->next_aggregation_sis = next_aggregation_sis + + ctx->attrs.aggr_interval / sample_interval; kdamond_merge_regions(ctx, max_nr_accesses / 10, sz_limit); @@ -1407,7 +1402,10 @@ static int kdamond_fn(void *data) ctx->ops.reset_aggregated(ctx); }

- if (kdamond_need_update_operations(ctx)) { + if (ctx->passed_sample_intervals == next_ops_update_sis) { + ctx->next_ops_update_sis = next_ops_update_sis + + ctx->attrs.ops_update_interval / + sample_interval; if (ctx->ops.update) ctx->ops.update(ctx); sz_limit = damon_region_sz_limit(ctx);