mm/damon/core.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-)
From: Bijan Tabatabai <bijantabatab@micron.com>
In damon_set_attrs(), ctx->next_{aggregation,ops_update}_sis would be
reset, even if the sample interval, aggregation interval, or ops update
interval were not changed. If damon_set_attrs() is called relatively
frequently, such as by frequent "commit" operations, aggregation and ops
update operations could be needlessly delayed.
This patch avoids this by only updating next_{aggregation,ops_update}_sis
if the relevant intervals were changed.
Cc: Bijan Tabatabai <bijan311@gmail.com>
Signed-off-by: Bijan Tabatabai <bijantabatab@micron.com>
---
This patch came from discussions in [1].
[1] https://lore.kernel.org/all/20250805162022.4920-1-bijan311@gmail.com/
---
mm/damon/core.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 6a2fe1f2c952..1c3d8b92257c 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -693,6 +693,12 @@ int damon_set_attrs(struct damon_ctx *ctx, struct damon_attrs *attrs)
unsigned long sample_interval = attrs->sample_interval ?
attrs->sample_interval : 1;
struct damos *s;
+ bool sample_interval_changed = ctx->attrs.sample_interval !=
+ attrs->sample_interval;
+ bool aggr_interval_changed = ctx->attrs.aggr_interval !=
+ attrs->aggr_interval;
+ bool ops_update_interval_changed = ctx->attrs.ops_update_interval !=
+ attrs->ops_update_interval;
bool aggregating = ctx->passed_sample_intervals <
ctx->next_aggregation_sis;
@@ -710,10 +716,12 @@ int damon_set_attrs(struct damon_ctx *ctx, struct damon_attrs *attrs)
if (!attrs->aggr_samples)
attrs->aggr_samples = attrs->aggr_interval / sample_interval;
- 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;
+ if (sample_interval_changed || aggr_interval_changed)
+ ctx->next_aggregation_sis = ctx->passed_sample_intervals +
+ attrs->aggr_interval / sample_interval;
+ if (sample_interval_changed || ops_update_interval_changed)
+ ctx->next_ops_update_sis = ctx->passed_sample_intervals +
+ attrs->ops_update_interval / sample_interval;
damon_update_monitoring_results(ctx, attrs, aggregating);
ctx->attrs = *attrs;
--
2.43.0Hi Bijan,
On Wed, 6 Aug 2025 11:43:16 -0500 Bijan Tabatabai <bijan311@gmail.com> wrote:
> From: Bijan Tabatabai <bijantabatab@micron.com>
>
> In damon_set_attrs(), ctx->next_{aggregation,ops_update}_sis would be
> reset, even if the sample interval, aggregation interval, or ops update
> interval were not changed. If damon_set_attrs() is called relatively
> frequently, such as by frequent "commit" operations, aggregation and ops
> update operations could be needlessly delayed.
>
> This patch avoids this by only updating next_{aggregation,ops_update}_sis
> if the relevant intervals were changed.
>
> Cc: Bijan Tabatabai <bijan311@gmail.com>
> Signed-off-by: Bijan Tabatabai <bijantabatab@micron.com>
> ---
> This patch came from discussions in [1].
>
> [1] https://lore.kernel.org/all/20250805162022.4920-1-bijan311@gmail.com/
Thank you for sending this patch as we discussed on the thread!
> ---
> mm/damon/core.c | 16 ++++++++++++----
> 1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index 6a2fe1f2c952..1c3d8b92257c 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -693,6 +693,12 @@ int damon_set_attrs(struct damon_ctx *ctx, struct damon_attrs *attrs)
> unsigned long sample_interval = attrs->sample_interval ?
> attrs->sample_interval : 1;
> struct damos *s;
> + bool sample_interval_changed = ctx->attrs.sample_interval !=
> + attrs->sample_interval;
> + bool aggr_interval_changed = ctx->attrs.aggr_interval !=
> + attrs->aggr_interval;
> + bool ops_update_interval_changed = ctx->attrs.ops_update_interval !=
> + attrs->ops_update_interval;
> bool aggregating = ctx->passed_sample_intervals <
> ctx->next_aggregation_sis;
>
> @@ -710,10 +716,12 @@ int damon_set_attrs(struct damon_ctx *ctx, struct damon_attrs *attrs)
> if (!attrs->aggr_samples)
> attrs->aggr_samples = attrs->aggr_interval / sample_interval;
>
> - 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;
> + if (sample_interval_changed || aggr_interval_changed)
> + ctx->next_aggregation_sis = ctx->passed_sample_intervals +
> + attrs->aggr_interval / sample_interval;
> + if (sample_interval_changed || ops_update_interval_changed)
> + ctx->next_ops_update_sis = ctx->passed_sample_intervals +
> + attrs->ops_update_interval / sample_interval;
>
> damon_update_monitoring_results(ctx, attrs, aggregating);
> ctx->attrs = *attrs;
Long story short, this (original) code is bit complicated and hence I suggest
to make this change less optimum but simpler.
damon_update_monitoring_results() assumes it is called only just after
next_{aggr,ops_update}_sis are updated. And the assumption is important for
the pseudo-moving-sum access frequency maintenance. As a result, this can make
the monitoring results temporarily corrupted, and splat warning once. Please
refer to commit 591c4c78be063 ("mm/damon/core: warn and fix nr_accesses[_bp]
corruption") or the patch thread[1] if you want more details.
Also damon_set_attrs() is called not only from commit situation. So I think
this maybe not an ideal part to modify.
What about modifying damon_commit_ctx() to check if new and old
damon_ctx->attrs are entirely same, and skip calling damon_set_attrs() in the
case? Doing the entire damon_attrs comparison might be suboptimum, but would
make the change simpler. I assume the suboptimum comparison is not a real
problem for your use case, so I think that could be a good tradeoff?
Also, I realize the moving sum access frequencies maintenance and
damon_set_attrs() are not well documented and organized. I will try to make
those better cleaned up and documented.
[1] https://lkml.kernel.org/r/20250513002715.40126-2-sj@kernel.org
Thanks,
SJ
> --
> 2.43.0
On Wed, Aug 6, 2025 at 2:09 PM SeongJae Park <sj@kernel.org> wrote:
>
> Hi Bijan,
>
> On Wed, 6 Aug 2025 11:43:16 -0500 Bijan Tabatabai <bijan311@gmail.com> wrote:
>
> > From: Bijan Tabatabai <bijantabatab@micron.com>
> >
> > In damon_set_attrs(), ctx->next_{aggregation,ops_update}_sis would be
> > reset, even if the sample interval, aggregation interval, or ops update
> > interval were not changed. If damon_set_attrs() is called relatively
> > frequently, such as by frequent "commit" operations, aggregation and ops
> > update operations could be needlessly delayed.
> >
> > This patch avoids this by only updating next_{aggregation,ops_update}_sis
> > if the relevant intervals were changed.
> >
> > Cc: Bijan Tabatabai <bijan311@gmail.com>
> > Signed-off-by: Bijan Tabatabai <bijantabatab@micron.com>
> > ---
> > This patch came from discussions in [1].
> >
> > [1] https://lore.kernel.org/all/20250805162022.4920-1-bijan311@gmail.com/
>
> Thank you for sending this patch as we discussed on the thread!
>
> > ---
> > mm/damon/core.c | 16 ++++++++++++----
> > 1 file changed, 12 insertions(+), 4 deletions(-)
> >
> > diff --git a/mm/damon/core.c b/mm/damon/core.c
> > index 6a2fe1f2c952..1c3d8b92257c 100644
> > --- a/mm/damon/core.c
> > +++ b/mm/damon/core.c
> > @@ -693,6 +693,12 @@ int damon_set_attrs(struct damon_ctx *ctx, struct damon_attrs *attrs)
> > unsigned long sample_interval = attrs->sample_interval ?
> > attrs->sample_interval : 1;
> > struct damos *s;
> > + bool sample_interval_changed = ctx->attrs.sample_interval !=
> > + attrs->sample_interval;
> > + bool aggr_interval_changed = ctx->attrs.aggr_interval !=
> > + attrs->aggr_interval;
> > + bool ops_update_interval_changed = ctx->attrs.ops_update_interval !=
> > + attrs->ops_update_interval;
> > bool aggregating = ctx->passed_sample_intervals <
> > ctx->next_aggregation_sis;
> >
> > @@ -710,10 +716,12 @@ int damon_set_attrs(struct damon_ctx *ctx, struct damon_attrs *attrs)
> > if (!attrs->aggr_samples)
> > attrs->aggr_samples = attrs->aggr_interval / sample_interval;
> >
> > - 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;
> > + if (sample_interval_changed || aggr_interval_changed)
> > + ctx->next_aggregation_sis = ctx->passed_sample_intervals +
> > + attrs->aggr_interval / sample_interval;
> > + if (sample_interval_changed || ops_update_interval_changed)
> > + ctx->next_ops_update_sis = ctx->passed_sample_intervals +
> > + attrs->ops_update_interval / sample_interval;
> >
> > damon_update_monitoring_results(ctx, attrs, aggregating);
> > ctx->attrs = *attrs;
>
> Long story short, this (original) code is bit complicated and hence I suggest
> to make this change less optimum but simpler.
>
> damon_update_monitoring_results() assumes it is called only just after
> next_{aggr,ops_update}_sis are updated. And the assumption is important for
> the pseudo-moving-sum access frequency maintenance. As a result, this can make
> the monitoring results temporarily corrupted, and splat warning once. Please
> refer to commit 591c4c78be063 ("mm/damon/core: warn and fix nr_accesses[_bp]
> corruption") or the patch thread[1] if you want more details.
>
> Also damon_set_attrs() is called not only from commit situation. So I think
> this maybe not an ideal part to modify.
>
> What about modifying damon_commit_ctx() to check if new and old
> damon_ctx->attrs are entirely same, and skip calling damon_set_attrs() in the
> case? Doing the entire damon_attrs comparison might be suboptimum, but would
> make the change simpler. I assume the suboptimum comparison is not a real
> problem for your use case, so I think that could be a good tradeoff?
I can definitely do this. Checking a few extra fields is no big deal.
Silly question, but think it's best to get it out of the way before
sending another patch: do you think there's a more elegant way of just
having a dumb comparison function like
bool damon_attrs_equal(struct damon_attrs *a, struct damon_attrs *b)
{
return a->sample_interval == b->sample_interval &&
a->aggr_interval == b->aggr_interval &&
...
}
And I assume I shouldn't compare the aggr_samples field because it's
private, is that right?
[...]
Thanks for your patience,
Bijan
On Wed, 6 Aug 2025 14:49:21 -0500 Bijan Tabatabai <bijan311@gmail.com> wrote:
> On Wed, Aug 6, 2025 at 2:09 PM SeongJae Park <sj@kernel.org> wrote:
> >
> > Hi Bijan,
> >
> > On Wed, 6 Aug 2025 11:43:16 -0500 Bijan Tabatabai <bijan311@gmail.com> wrote:
> >
> > > From: Bijan Tabatabai <bijantabatab@micron.com>
> > >
> > > In damon_set_attrs(), ctx->next_{aggregation,ops_update}_sis would be
> > > reset, even if the sample interval, aggregation interval, or ops update
> > > interval were not changed. If damon_set_attrs() is called relatively
> > > frequently, such as by frequent "commit" operations, aggregation and ops
> > > update operations could be needlessly delayed.
> > >
> > > This patch avoids this by only updating next_{aggregation,ops_update}_sis
> > > if the relevant intervals were changed.
[...]
> > What about modifying damon_commit_ctx() to check if new and old
> > damon_ctx->attrs are entirely same, and skip calling damon_set_attrs() in the
> > case? Doing the entire damon_attrs comparison might be suboptimum, but would
> > make the change simpler. I assume the suboptimum comparison is not a real
> > problem for your use case, so I think that could be a good tradeoff?
>
> I can definitely do this. Checking a few extra fields is no big deal.
>
> Silly question, but think it's best to get it out of the way before
> sending another patch: do you think there's a more elegant way of just
> having a dumb comparison function like
>
> bool damon_attrs_equal(struct damon_attrs *a, struct damon_attrs *b)
> {
> return a->sample_interval == b->sample_interval &&
> a->aggr_interval == b->aggr_interval &&
> ...
> }
>
> And I assume I shouldn't compare the aggr_samples field because it's
> private, is that right?
Ah, you're right, thank you for asking this!
Maybe we can copy src->attrs to a local damon_attrs variable, overwrite
aggr_samples of the copy and dst, and memcmp() the copy and dst?
I wouldn't mind the dumb comparison function, though, if you prefer. I'll
defer the decision to you!
Thanks,
SJ
[...]
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