should_proactive_compact_node() returns true when sum of the
weighted fragmentation score of all the zones in the node is greater
than the wmark_high of compaction, which then triggers the proactive
compaction that operates on the individual zones of the node. But
proactive compaction runs on the zone only when its weighted
fragmentation score is greater than wmark_low(=wmark_high - 10).
This means that the sum of the weighted fragmentation scores of all the
zones can exceed the wmark_high but individual weighted fragmentation
zone scores can still be less than wmark_low which makes the unnecessary
trigger of the proactive compaction only to return doing nothing.
Issue with the return of proactive compaction with out even trying is
its deferral. It is simply deferred for 1 << COMPACT_MAX_DEFER_SHIFT if
the scores across the proactive compaction is same, thinking that
compaction didn't make any progress but in reality it didn't even try.
With the delay between successive retries for proactive compaction is
500msec, it can result into the deferral for ~30sec with out even trying
the proactive compaction.
Test scenario is that: compaction_proactiveness=50 thus the wmark_low =
50 and wmark_high = 60. System have 2 zones(Normal and Movable) with
sizes 5GB and 6GB respectively. After opening some apps on the android,
the weighted fragmentation scores of these zones are 47 and 49
respectively. Since the sum of these fragmentation scores are above the
wmark_high which triggers the proactive compaction and there since the
individual zones weighted fragmentation scores are below wmark_low, it
returns without trying the proactive compaction. As a result the
weighted fragmentation scores of the zones are still 47 and 49 which
makes the existing logic to defer the compaction thinking that
noprogress is made across the compaction.
Fix this by checking just zone fragmentation score, not the weighted, in
__compact_finished() and use the zones weighted fragmentation score in
fragmentation_score_node(). In the test case above, If the weighted
average of is above wmark_high, then individual score (not adjusted) of
atleast one zone has to be above wmark_high. Thus it avoids the
unnecessary trigger and deferrals of the proactive compaction.
Fix-suggested-by: Vlastimil Babka <[email protected]>
Signed-off-by: Charan Teja Reddy <[email protected]>
---
Changes in V3: Addressed suggestions from Vlastimil
Changes in V2: https://lore.kernel.org/patchwork/patch/1366862/
Changes in V1: https://lore.kernel.org/patchwork/patch/1364646/
mm/compaction.c | 20 ++++++++++++++------
1 file changed, 14 insertions(+), 6 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index e5acb97..ccddb3a 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1925,20 +1925,28 @@ static bool kswapd_is_running(pg_data_t *pgdat)
/*
* A zone's fragmentation score is the external fragmentation wrt to the
- * COMPACTION_HPAGE_ORDER scaled by the zone's size. It returns a value
- * in the range [0, 100].
+ * COMPACTION_HPAGE_ORDER. It returns a value in the range [0, 100].
+ */
+static unsigned int fragmentation_score_zone(struct zone *zone)
+{
+ return extfrag_for_order(zone, COMPACTION_HPAGE_ORDER);
+}
+
+/*
+ * A weighted zone's fragmentation score is the external fragmentation
+ * wrt to the COMPACTION_HPAGE_ORDER scaled by the zone's size. It
+ * returns a value in the range [0, 100].
*
* The scaling factor ensures that proactive compaction focuses on larger
* zones like ZONE_NORMAL, rather than smaller, specialized zones like
* ZONE_DMA32. For smaller zones, the score value remains close to zero,
* and thus never exceeds the high threshold for proactive compaction.
*/
-static unsigned int fragmentation_score_zone(struct zone *zone)
+static unsigned int fragmentation_score_zone_weighted(struct zone *zone)
{
unsigned long score;
- score = zone->present_pages *
- extfrag_for_order(zone, COMPACTION_HPAGE_ORDER);
+ score = zone->present_pages * fragmentation_score_zone(zone);
return div64_ul(score, zone->zone_pgdat->node_present_pages + 1);
}
@@ -1958,7 +1966,7 @@ static unsigned int fragmentation_score_node(pg_data_t *pgdat)
struct zone *zone;
zone = &pgdat->node_zones[zoneid];
- score += fragmentation_score_zone(zone);
+ score += fragmentation_score_zone_weighted(zone);
}
return score;
--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
member of the Code Aurora Forum, hosted by The Linux Foundation
On 1/18/21 6:12 PM, Charan Teja Reddy wrote:
> should_proactive_compact_node() returns true when sum of the
> weighted fragmentation score of all the zones in the node is greater
> than the wmark_high of compaction, which then triggers the proactive
> compaction that operates on the individual zones of the node. But
> proactive compaction runs on the zone only when its weighted
> fragmentation score is greater than wmark_low(=wmark_high - 10).
>
> This means that the sum of the weighted fragmentation scores of all the
> zones can exceed the wmark_high but individual weighted fragmentation
> zone scores can still be less than wmark_low which makes the unnecessary
> trigger of the proactive compaction only to return doing nothing.
>
> Issue with the return of proactive compaction with out even trying is
> its deferral. It is simply deferred for 1 << COMPACT_MAX_DEFER_SHIFT if
> the scores across the proactive compaction is same, thinking that
> compaction didn't make any progress but in reality it didn't even try.
> With the delay between successive retries for proactive compaction is
> 500msec, it can result into the deferral for ~30sec with out even trying
> the proactive compaction.
>
> Test scenario is that: compaction_proactiveness=50 thus the wmark_low =
> 50 and wmark_high = 60. System have 2 zones(Normal and Movable) with
> sizes 5GB and 6GB respectively. After opening some apps on the android,
> the weighted fragmentation scores of these zones are 47 and 49
> respectively. Since the sum of these fragmentation scores are above the
> wmark_high which triggers the proactive compaction and there since the
> individual zones weighted fragmentation scores are below wmark_low, it
> returns without trying the proactive compaction. As a result the
> weighted fragmentation scores of the zones are still 47 and 49 which
> makes the existing logic to defer the compaction thinking that
> noprogress is made across the compaction.
>
> Fix this by checking just zone fragmentation score, not the weighted, in
> __compact_finished() and use the zones weighted fragmentation score in
> fragmentation_score_node(). In the test case above, If the weighted
> average of is above wmark_high, then individual score (not adjusted) of
> atleast one zone has to be above wmark_high. Thus it avoids the
> unnecessary trigger and deferrals of the proactive compaction.
>
> Fix-suggested-by: Vlastimil Babka <[email protected]>
> Signed-off-by: Charan Teja Reddy <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Thanks!
On 1/18/21 10:12 AM, Charan Teja Reddy wrote:
> should_proactive_compact_node() returns true when sum of the
> weighted fragmentation score of all the zones in the node is greater
> than the wmark_high of compaction, which then triggers the proactive
> compaction that operates on the individual zones of the node. But
> proactive compaction runs on the zone only when its weighted
> fragmentation score is greater than wmark_low(=wmark_high - 10).
>
> This means that the sum of the weighted fragmentation scores of all the
> zones can exceed the wmark_high but individual weighted fragmentation
> zone scores can still be less than wmark_low which makes the unnecessary
> trigger of the proactive compaction only to return doing nothing.
>
> Issue with the return of proactive compaction with out even trying is
> its deferral. It is simply deferred for 1 << COMPACT_MAX_DEFER_SHIFT if
> the scores across the proactive compaction is same, thinking that
> compaction didn't make any progress but in reality it didn't even try.
> With the delay between successive retries for proactive compaction is
> 500msec, it can result into the deferral for ~30sec with out even trying
> the proactive compaction.
>
> Test scenario is that: compaction_proactiveness=50 thus the wmark_low =
> 50 and wmark_high = 60. System have 2 zones(Normal and Movable) with
> sizes 5GB and 6GB respectively. After opening some apps on the android,
> the weighted fragmentation scores of these zones are 47 and 49
> respectively. Since the sum of these fragmentation scores are above the
> wmark_high which triggers the proactive compaction and there since the
> individual zones weighted fragmentation scores are below wmark_low, it
> returns without trying the proactive compaction. As a result the
> weighted fragmentation scores of the zones are still 47 and 49 which
> makes the existing logic to defer the compaction thinking that
> noprogress is made across the compaction.
>
> Fix this by checking just zone fragmentation score, not the weighted, in
> __compact_finished() and use the zones weighted fragmentation score in
> fragmentation_score_node(). In the test case above, If the weighted
> average of is above wmark_high, then individual score (not adjusted) of
> atleast one zone has to be above wmark_high. Thus it avoids the
> unnecessary trigger and deferrals of the proactive compaction.
>
> Fix-suggested-by: Vlastimil Babka <[email protected]>
> Signed-off-by: Charan Teja Reddy <[email protected]>
> ---
>
> Changes in V3: Addressed suggestions from Vlastimil
>
> Changes in V2: https://lore.kernel.org/patchwork/patch/1366862/
>
> Changes in V1: https://lore.kernel.org/patchwork/patch/1364646/
>
> mm/compaction.c | 20 ++++++++++++++------
> 1 file changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index e5acb97..ccddb3a 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1925,20 +1925,28 @@ static bool kswapd_is_running(pg_data_t *pgdat)
>
> /*
> * A zone's fragmentation score is the external fragmentation wrt to the
> - * COMPACTION_HPAGE_ORDER scaled by the zone's size. It returns a value
> - * in the range [0, 100].
> + * COMPACTION_HPAGE_ORDER. It returns a value in the range [0, 100].
> + */
> +static unsigned int fragmentation_score_zone(struct zone *zone)
> +{
> + return extfrag_for_order(zone, COMPACTION_HPAGE_ORDER);
> +}
> +
> +/*
> + * A weighted zone's fragmentation score is the external fragmentation
> + * wrt to the COMPACTION_HPAGE_ORDER scaled by the zone's size. It
> + * returns a value in the range [0, 100].
> *
> * The scaling factor ensures that proactive compaction focuses on larger
> * zones like ZONE_NORMAL, rather than smaller, specialized zones like
> * ZONE_DMA32. For smaller zones, the score value remains close to zero,
> * and thus never exceeds the high threshold for proactive compaction.
> */
> -static unsigned int fragmentation_score_zone(struct zone *zone)
> +static unsigned int fragmentation_score_zone_weighted(struct zone *zone)
> {
> unsigned long score;
>
> - score = zone->present_pages *
> - extfrag_for_order(zone, COMPACTION_HPAGE_ORDER);
> + score = zone->present_pages * fragmentation_score_zone(zone);
> return div64_ul(score, zone->zone_pgdat->node_present_pages + 1);
> }
>
> @@ -1958,7 +1966,7 @@ static unsigned int fragmentation_score_node(pg_data_t *pgdat)
> struct zone *zone;
>
> zone = &pgdat->node_zones[zoneid];
> - score += fragmentation_score_zone(zone);
> + score += fragmentation_score_zone_weighted(zone);
> }
>
> return score;
>
Looks good.
Reviewed-by: Khalid Aziz <[email protected]>
On Mon, 18 Jan 2021, Charan Teja Reddy wrote:
> should_proactive_compact_node() returns true when sum of the
> weighted fragmentation score of all the zones in the node is greater
> than the wmark_high of compaction, which then triggers the proactive
> compaction that operates on the individual zones of the node. But
> proactive compaction runs on the zone only when its weighted
> fragmentation score is greater than wmark_low(=wmark_high - 10).
>
> This means that the sum of the weighted fragmentation scores of all the
> zones can exceed the wmark_high but individual weighted fragmentation
> zone scores can still be less than wmark_low which makes the unnecessary
> trigger of the proactive compaction only to return doing nothing.
>
> Issue with the return of proactive compaction with out even trying is
> its deferral. It is simply deferred for 1 << COMPACT_MAX_DEFER_SHIFT if
> the scores across the proactive compaction is same, thinking that
> compaction didn't make any progress but in reality it didn't even try.
Isn't this an issue in deferred compaction as well? It seems like
deferred compaction should check that work was actually performed before
deferring subsequent calls to compaction.
In other words, I don't believe deferred compaction is intended to avoid
checks to determine if compaction is worth it; it should only defer
*additional* work that was not productive.
Thoughts?
> With the delay between successive retries for proactive compaction is
> 500msec, it can result into the deferral for ~30sec with out even trying
> the proactive compaction.
>
> Test scenario is that: compaction_proactiveness=50 thus the wmark_low =
> 50 and wmark_high = 60. System have 2 zones(Normal and Movable) with
> sizes 5GB and 6GB respectively. After opening some apps on the android,
> the weighted fragmentation scores of these zones are 47 and 49
> respectively. Since the sum of these fragmentation scores are above the
> wmark_high which triggers the proactive compaction and there since the
> individual zones weighted fragmentation scores are below wmark_low, it
> returns without trying the proactive compaction. As a result the
> weighted fragmentation scores of the zones are still 47 and 49 which
> makes the existing logic to defer the compaction thinking that
> noprogress is made across the compaction.
>
> Fix this by checking just zone fragmentation score, not the weighted, in
> __compact_finished() and use the zones weighted fragmentation score in
> fragmentation_score_node(). In the test case above, If the weighted
> average of is above wmark_high, then individual score (not adjusted) of
> atleast one zone has to be above wmark_high. Thus it avoids the
> unnecessary trigger and deferrals of the proactive compaction.
>
> Fix-suggested-by: Vlastimil Babka <[email protected]>
Suggested-by
> Signed-off-by: Charan Teja Reddy <[email protected]>
Acked-by: David Rientjes <[email protected]>
On 1/19/21 8:26 PM, David Rientjes wrote:
> On Mon, 18 Jan 2021, Charan Teja Reddy wrote:
>
>> should_proactive_compact_node() returns true when sum of the
>> weighted fragmentation score of all the zones in the node is greater
>> than the wmark_high of compaction, which then triggers the proactive
>> compaction that operates on the individual zones of the node. But
>> proactive compaction runs on the zone only when its weighted
>> fragmentation score is greater than wmark_low(=wmark_high - 10).
>>
>> This means that the sum of the weighted fragmentation scores of all the
>> zones can exceed the wmark_high but individual weighted fragmentation
>> zone scores can still be less than wmark_low which makes the unnecessary
>> trigger of the proactive compaction only to return doing nothing.
>>
>> Issue with the return of proactive compaction with out even trying is
>> its deferral. It is simply deferred for 1 << COMPACT_MAX_DEFER_SHIFT if
>> the scores across the proactive compaction is same, thinking that
>> compaction didn't make any progress but in reality it didn't even try.
>
> Isn't this an issue in deferred compaction as well? It seems like
> deferred compaction should check that work was actually performed before
> deferring subsequent calls to compaction.
Direct compaction does, proactive not.
> In other words, I don't believe deferred compaction is intended to avoid
> checks to determine if compaction is worth it; it should only defer
> *additional* work that was not productive.
Yeah, that should be more optimal.
> Thoughts?
>
On Wed, 20 Jan 2021, Vlastimil Babka wrote:
> On 1/19/21 8:26 PM, David Rientjes wrote:
> > On Mon, 18 Jan 2021, Charan Teja Reddy wrote:
> >
> >> should_proactive_compact_node() returns true when sum of the
> >> weighted fragmentation score of all the zones in the node is greater
> >> than the wmark_high of compaction, which then triggers the proactive
> >> compaction that operates on the individual zones of the node. But
> >> proactive compaction runs on the zone only when its weighted
> >> fragmentation score is greater than wmark_low(=wmark_high - 10).
> >>
> >> This means that the sum of the weighted fragmentation scores of all the
> >> zones can exceed the wmark_high but individual weighted fragmentation
> >> zone scores can still be less than wmark_low which makes the unnecessary
> >> trigger of the proactive compaction only to return doing nothing.
> >>
> >> Issue with the return of proactive compaction with out even trying is
> >> its deferral. It is simply deferred for 1 << COMPACT_MAX_DEFER_SHIFT if
> >> the scores across the proactive compaction is same, thinking that
> >> compaction didn't make any progress but in reality it didn't even try.
> >
> > Isn't this an issue in deferred compaction as well? It seems like
> > deferred compaction should check that work was actually performed before
> > deferring subsequent calls to compaction.
>
> Direct compaction does, proactive not.
>
> > In other words, I don't believe deferred compaction is intended to avoid
> > checks to determine if compaction is worth it; it should only defer
> > *additional* work that was not productive.
>
> Yeah, that should be more optimal.
>
Charan, is this something you'd like to follow up on, or should I take a
look instead?
Thanks!
On 1/18/21 6:12 PM, Charan Teja Reddy wrote:
> should_proactive_compact_node() returns true when sum of the
> weighted fragmentation score of all the zones in the node is greater
> than the wmark_high of compaction, which then triggers the proactive
> compaction that operates on the individual zones of the node. But
> proactive compaction runs on the zone only when its weighted
> fragmentation score is greater than wmark_low(=wmark_high - 10).
>
> This means that the sum of the weighted fragmentation scores of all the
> zones can exceed the wmark_high but individual weighted fragmentation
> zone scores can still be less than wmark_low which makes the unnecessary
> trigger of the proactive compaction only to return doing nothing.
>
> Issue with the return of proactive compaction with out even trying is
> its deferral. It is simply deferred for 1 << COMPACT_MAX_DEFER_SHIFT if
> the scores across the proactive compaction is same, thinking that
> compaction didn't make any progress but in reality it didn't even try.
> With the delay between successive retries for proactive compaction is
> 500msec, it can result into the deferral for ~30sec with out even trying
> the proactive compaction.
>
> Test scenario is that: compaction_proactiveness=50 thus the wmark_low =
> 50 and wmark_high = 60. System have 2 zones(Normal and Movable) with
> sizes 5GB and 6GB respectively. After opening some apps on the android,
> the weighted fragmentation scores of these zones are 47 and 49
> respectively. Since the sum of these fragmentation scores are above the
> wmark_high which triggers the proactive compaction and there since the
> individual zones weighted fragmentation scores are below wmark_low, it
> returns without trying the proactive compaction. As a result the
> weighted fragmentation scores of the zones are still 47 and 49 which
> makes the existing logic to defer the compaction thinking that
> noprogress is made across the compaction.
>
> Fix this by checking just zone fragmentation score, not the weighted, in
> __compact_finished() and use the zones weighted fragmentation score in
> fragmentation_score_node(). In the test case above, If the weighted
> average of is above wmark_high, then individual score (not adjusted) of
> atleast one zone has to be above wmark_high. Thus it avoids the
> unnecessary trigger and deferrals of the proactive compaction.
>
> Fix-suggested-by: Vlastimil Babka <[email protected]>
> Signed-off-by: Charan Teja Reddy <[email protected]>
> ---
>
> Changes in V3: Addressed suggestions from Vlastimil
>
> Changes in V2: https://lore.kernel.org/patchwork/patch/1366862/
>
> Changes in V1: https://lore.kernel.org/patchwork/patch/1364646/
Andrew, I've noticed that v1 is still in mmotm [1] together with v3, which
doesn't make sense together, please drop [1]. Thanks
[1]
https://www.ozlabs.org/~akpm/mmots/broken-out/mm-compaction-return-proper-state-in-should_proactive_compact_node.patch
> mm/compaction.c | 20 ++++++++++++++------
> 1 file changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index e5acb97..ccddb3a 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1925,20 +1925,28 @@ static bool kswapd_is_running(pg_data_t *pgdat)
>
> /*
> * A zone's fragmentation score is the external fragmentation wrt to the
> - * COMPACTION_HPAGE_ORDER scaled by the zone's size. It returns a value
> - * in the range [0, 100].
> + * COMPACTION_HPAGE_ORDER. It returns a value in the range [0, 100].
> + */
> +static unsigned int fragmentation_score_zone(struct zone *zone)
> +{
> + return extfrag_for_order(zone, COMPACTION_HPAGE_ORDER);
> +}
> +
> +/*
> + * A weighted zone's fragmentation score is the external fragmentation
> + * wrt to the COMPACTION_HPAGE_ORDER scaled by the zone's size. It
> + * returns a value in the range [0, 100].
> *
> * The scaling factor ensures that proactive compaction focuses on larger
> * zones like ZONE_NORMAL, rather than smaller, specialized zones like
> * ZONE_DMA32. For smaller zones, the score value remains close to zero,
> * and thus never exceeds the high threshold for proactive compaction.
> */
> -static unsigned int fragmentation_score_zone(struct zone *zone)
> +static unsigned int fragmentation_score_zone_weighted(struct zone *zone)
> {
> unsigned long score;
>
> - score = zone->present_pages *
> - extfrag_for_order(zone, COMPACTION_HPAGE_ORDER);
> + score = zone->present_pages * fragmentation_score_zone(zone);
> return div64_ul(score, zone->zone_pgdat->node_present_pages + 1);
> }
>
> @@ -1958,7 +1966,7 @@ static unsigned int fragmentation_score_node(pg_data_t *pgdat)
> struct zone *zone;
>
> zone = &pgdat->node_zones[zoneid];
> - score += fragmentation_score_zone(zone);
> + score += fragmentation_score_zone_weighted(zone);
> }
>
> return score;
>
On 1/25/2021 4:24 AM, David Rientjes wrote:
> On Wed, 20 Jan 2021, Vlastimil Babka wrote:
>
>> On 1/19/21 8:26 PM, David Rientjes wrote:
>>> On Mon, 18 Jan 2021, Charan Teja Reddy wrote:
>>>
>>>> should_proactive_compact_node() returns true when sum of the
>>>> weighted fragmentation score of all the zones in the node is greater
>>>> than the wmark_high of compaction, which then triggers the proactive
>>>> compaction that operates on the individual zones of the node. But
>>>> proactive compaction runs on the zone only when its weighted
>>>> fragmentation score is greater than wmark_low(=wmark_high - 10).
>>>>
>>>> This means that the sum of the weighted fragmentation scores of all the
>>>> zones can exceed the wmark_high but individual weighted fragmentation
>>>> zone scores can still be less than wmark_low which makes the unnecessary
>>>> trigger of the proactive compaction only to return doing nothing.
>>>>
>>>> Issue with the return of proactive compaction with out even trying is
>>>> its deferral. It is simply deferred for 1 << COMPACT_MAX_DEFER_SHIFT if
>>>> the scores across the proactive compaction is same, thinking that
>>>> compaction didn't make any progress but in reality it didn't even try.
>>>
>>> Isn't this an issue in deferred compaction as well? It seems like
>>> deferred compaction should check that work was actually performed before
>>> deferring subsequent calls to compaction.
>>
>> Direct compaction does, proactive not.
>>
>>> In other words, I don't believe deferred compaction is intended to avoid
>>> checks to determine if compaction is worth it; it should only defer
>>> *additional* work that was not productive.
>>
>> Yeah, that should be more optimal.
>>
>
> Charan, is this something you'd like to follow up on, or should I take a
> look instead?
>
Sure David. Happy to follow up on this. Thanks!
> Thanks!
>
--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
Forum, a Linux Foundation Collaborative Project