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Date: Fri, 31 May 2024 12:38:38 -0700
From: SeongJae Park <sj@...nel.org>
To: Alex Rusuf <yorha.op@...il.com>
Cc: SeongJae Park <sj@...nel.org>,
damon@...ts.linux.dev,
linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] mm/damon/core: implement multi-context support
Hi Alex,
On Fri, 31 May 2024 15:23:20 +0300 Alex Rusuf <yorha.op@...il.com> wrote:
> This patch actually implements support for
> multi-context design for kdamond daemon.
>
> In pseudo code previous versions worked like
> the following:
>
> while (!kdamond_should_stop()) {
>
> /* prepare accesses for only 1 context */
> prepare_accesses(damon_context);
>
> sleep(sample_interval);
>
> /* check accesses for only 1 context */
> check_accesses(damon_context);
>
> ...
> }
>
> With this patch kdamond workflow will look
> like the following:
>
> while (!kdamond_shoule_stop()) {
>
> /* prepare accesses for all contexts in kdamond */
> damon_for_each_context(ctx, kdamond)
> prepare_accesses(ctx);
>
> sleep(sample_interval);
>
> /* check_accesses for all contexts in kdamond */
> damon_for_each_context(ctx, kdamond)
> check_accesses(ctx);
>
> ...
> }
This is not what you do now, but on previous patch, right? Let's modify the
mesage appropriately.
>
> Another point to note is watermarks. Previous versions
> checked watermarks on each iteration for current context
> and if matric's value wan't acceptable kdamond waited
> for watermark's sleep interval.
Mention changes of versions on cover letter.
>
> Now there's no need to wait for each context, we can
> just skip context if watermark's metric isn't ready,
> but if there's no contexts that can run we
> check for each context's watermark metric and
> sleep for the lowest interval of all contexts.
>
> Signed-off-by: Alex Rusuf <yorha.op@...il.com>
> ---
> include/linux/damon.h | 11 +-
> include/trace/events/damon.h | 14 +-
> mm/damon/core-test.h | 2 +-
> mm/damon/core.c | 286 +++++++++++++++++------------
> mm/damon/dbgfs-test.h | 4 +-
> mm/damon/dbgfs.c | 342 +++++++++++++++++++++--------------
> mm/damon/modules-common.c | 1 -
> mm/damon/sysfs.c | 47 +++--
> 8 files changed, 431 insertions(+), 276 deletions(-)
>
> diff --git a/include/linux/damon.h b/include/linux/damon.h
> index 7cb9979a0..2facf3a5f 100644
> --- a/include/linux/damon.h
> +++ b/include/linux/damon.h
> @@ -575,7 +575,6 @@ struct damon_attrs {
> * @lock: Kdamond's global lock, serializes accesses to any field.
> * @self: Kernel thread which is actually being executed.
> * @contexts: Head of contexts (&damon_ctx) list.
> - * @nr_ctxs: Number of contexts being monitored.
> *
> * Each DAMON's background daemon has this structure. Once
> * configured, daemon can be started by calling damon_start().
> @@ -589,7 +588,6 @@ struct kdamond {
> struct mutex lock;
> struct task_struct *self;
> struct list_head contexts;
> - size_t nr_ctxs;
Why we add this on first patch, and then remove here? Let's not make
unnecessary temporal change. It only increase review time.
>
> /* private: */
> /* for waiting until the execution of the kdamond_fn is started */
> @@ -634,7 +632,10 @@ struct damon_ctx {
> * update
> */
> unsigned long next_ops_update_sis;
> + /* upper limit for each monitoring region */
> unsigned long sz_limit;
> + /* marker to check if context is valid */
> + bool valid;
What is the validity?
>
> /* public: */
> struct kdamond *kdamond;
> @@ -682,6 +683,12 @@ static inline struct damon_ctx *damon_first_ctx(struct kdamond *kdamond)
> return list_first_entry(&kdamond->contexts, struct damon_ctx, list);
> }
>
> +static inline bool damon_is_last_ctx(struct damon_ctx *ctx,
> + struct kdamond *kdamond)
> +{
> + return list_is_last(&ctx->list, &kdamond->contexts);
> +}
> +
> #define damon_for_each_region(r, t) \
> list_for_each_entry(r, &t->regions_list, list)
>
> diff --git a/include/trace/events/damon.h b/include/trace/events/damon.h
> index 23200aabc..d5287566c 100644
> --- a/include/trace/events/damon.h
> +++ b/include/trace/events/damon.h
Let's separate this change to another patch.
> @@ -50,12 +50,13 @@ TRACE_EVENT_CONDITION(damos_before_apply,
>
> TRACE_EVENT(damon_aggregated,
>
> - TP_PROTO(unsigned int target_id, struct damon_region *r,
> - unsigned int nr_regions),
> + TP_PROTO(unsigned int context_id, unsigned int target_id,
> + struct damon_region *r, unsigned int nr_regions),
>
> - TP_ARGS(target_id, r, nr_regions),
> + TP_ARGS(context_id, target_id, r, nr_regions),
>
> TP_STRUCT__entry(
> + __field(unsigned long, context_id)
> __field(unsigned long, target_id)
> __field(unsigned int, nr_regions)
> __field(unsigned long, start)
> @@ -65,6 +66,7 @@ TRACE_EVENT(damon_aggregated,
> ),
>
> TP_fast_assign(
> + __entry->context_id = context_id;
> __entry->target_id = target_id;
> __entry->nr_regions = nr_regions;
> __entry->start = r->ar.start;
> @@ -73,9 +75,9 @@ TRACE_EVENT(damon_aggregated,
> __entry->age = r->age;
> ),
>
> - TP_printk("target_id=%lu nr_regions=%u %lu-%lu: %u %u",
> - __entry->target_id, __entry->nr_regions,
> - __entry->start, __entry->end,
> + TP_printk("context_id=%lu target_id=%lu nr_regions=%u %lu-%lu: %u %u",
> + __entry->context_id, __entry->target_id,
> + __entry->nr_regions, __entry->start, __entry->end,
> __entry->nr_accesses, __entry->age)
> );
>
> diff --git a/mm/damon/core-test.h b/mm/damon/core-test.h
> index 0cee634f3..7962c9a0e 100644
> --- a/mm/damon/core-test.h
> +++ b/mm/damon/core-test.h
> @@ -99,7 +99,7 @@ static void damon_test_aggregate(struct kunit *test)
> }
> it++;
> }
> - kdamond_reset_aggregated(ctx);
> + kdamond_reset_aggregated(ctx, 0);
> it = 0;
> damon_for_each_target(t, ctx) {
> ir = 0;
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index cfc9c803d..ad73752af 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -500,6 +500,8 @@ struct damon_ctx *damon_new_ctx(void)
> ctx->attrs.min_nr_regions = 10;
> ctx->attrs.max_nr_regions = 1000;
>
> + ctx->valid = true;
> +
> INIT_LIST_HEAD(&ctx->adaptive_targets);
> INIT_LIST_HEAD(&ctx->schemes);
> INIT_LIST_HEAD(&ctx->list);
> @@ -513,7 +515,7 @@ struct damon_ctx *damon_new_ctx(void)
> void damon_add_ctx(struct kdamond *kdamond, struct damon_ctx *ctx)
> {
> list_add_tail(&ctx->list, &kdamond->contexts);
> - ++kdamond->nr_ctxs;
> + ctx->kdamond = kdamond;
> }
>
> struct kdamond *damon_new_kdamond(void)
> @@ -567,10 +569,8 @@ void damon_destroy_ctxs(struct kdamond *kdamond)
> {
> struct damon_ctx *c, *next;
>
> - damon_for_each_context_safe(c, next, kdamond) {
> + damon_for_each_context_safe(c, next, kdamond)
> damon_destroy_ctx(c);
> - --kdamond->nr_ctxs;
> - }
> }
>
> void damon_destroy_kdamond(struct kdamond *kdamond)
> @@ -735,6 +735,20 @@ bool damon_kdamond_running(struct kdamond *kdamond)
> return running;
> }
>
> +/**
> + * kdamond_nr_ctxs() - Return number of contexts for this kdamond.
> + */
> +static int kdamond_nr_ctxs(struct kdamond *kdamond)
> +{
> + struct list_head *pos;
> + int nr_ctxs = 0;
> +
> + list_for_each(pos, &kdamond->contexts)
> + ++nr_ctxs;
> +
> + return nr_ctxs;
> +}
> +
> /* Returns the size upper limit for each monitoring region */
> static unsigned long damon_region_sz_limit(struct damon_ctx *ctx)
> {
> @@ -793,11 +807,11 @@ static int __damon_start(struct kdamond *kdamond)
> * @exclusive: exclusiveness of this contexts group
> *
> * 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
> + * contexts. If @exclusive is true and a group of contexts that created by other
> * 'damon_start()' call is currently running, this function does nothing but
> - * returns -EBUSY.
> + * returns -EBUSY, if @exclusive is true and a given kdamond wants to run
> + * several contexts, then this function returns -EINVAL. kdamond can run
> + * exclusively only one context.
> *
> * Return: 0 on success, negative error code otherwise.
> */
> @@ -806,10 +820,6 @@ int damon_start(struct kdamond *kdamond, bool exclusive)
> int err = 0;
>
> BUG_ON(!kdamond);
> - BUG_ON(!kdamond->nr_ctxs);
> -
> - if (kdamond->nr_ctxs != 1)
> - return -EINVAL;
>
> mutex_lock(&damon_lock);
> if ((exclusive && nr_running_kdamonds) ||
> @@ -818,6 +828,11 @@ int damon_start(struct kdamond *kdamond, bool exclusive)
> return -EBUSY;
> }
>
> + if (exclusive && kdamond_nr_ctxs(kdamond) > 1) {
> + mutex_unlock(&damon_lock);
> + return -EINVAL;
> + }
> +
> err = __damon_start(kdamond);
> if (err)
> return err;
> @@ -857,7 +872,7 @@ int damon_stop(struct kdamond *kdamond)
> /*
> * Reset the aggregated monitoring results ('nr_accesses' of each region).
> */
> -static void kdamond_reset_aggregated(struct damon_ctx *c)
> +static void kdamond_reset_aggregated(struct damon_ctx *c, unsigned int ci)
> {
> struct damon_target *t;
> unsigned int ti = 0; /* target's index */
> @@ -866,7 +881,7 @@ static void kdamond_reset_aggregated(struct damon_ctx *c)
> struct damon_region *r;
>
> damon_for_each_region(r, t) {
> - trace_damon_aggregated(ti, r, damon_nr_regions(t));
> + trace_damon_aggregated(ci, ti, r, damon_nr_regions(t));
Separate traceevent change into another patch.
> r->last_nr_accesses = r->nr_accesses;
> r->nr_accesses = 0;
> }
> @@ -1033,21 +1048,15 @@ static bool damos_filter_out(struct damon_ctx *ctx, struct damon_target *t,
> return false;
> }
>
> -static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
> - struct damon_region *r, struct damos *s)
> +static void damos_apply_scheme(unsigned int cidx, struct damon_ctx *c,
> + struct damon_target *t, struct damon_region *r,
> + struct damos *s)
Unnecesary change.
As also mentioned on the reply to the first patch, I think this patch can
significantly changed if you agree to my opinion about the flow of patches that
I mentioned on the reply to the cover letter. Hence, stopping review from here
for now. Please let me know if you have a different opinion.
Thanks,
SJ
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