mm/damon/core: trace esz at first setup
Subsystems (3)
SeongJae Park
maintainerPATCH 1/1 mm/damon/core: trace esz at first setup
DAMON traces effective size quota from the second update, only if a change has been made by the update. Tracing only changed updates was an intentional decision to avoid unnecessary same value tracing. Always skipping the first value is just an unintended mistake.
The mistake makes the tracepoint based investigation incomplete, because the first effective size quota is never traced. It is not a big issue when the 'consist' quota tuner is used, because it keeps changing the quota in the usual setup.
However, when the 'temporal' tuner is used, the quota value is not changed before the goal achievement status is completely changed. For example, if the DAMOS scheme is started with an under-achieved goal, the quota is set to the maximum value, and kept the same value until the goal is achieved. Because DAMON skips the first value, the user cannot know what effective quota the current scheme is using. Only after the goal is achieved, the effective quota is changed to zero, and traced.
Unconditionally trace the initial quota value to fix this problem.
Note that the 'temporal' quota tuner was introduced by commit af738a6a00c1 ("mm/damon/core: introduce DAMOS_QUOTA_GOAL_TUNER_TEMPORAL"), which was added to 7.1-rc1. But even with the 'consist' quota tuner, the tracing is unintentionally incomplete. Hence this commit marks the introduction of the trace event as the broken commit.
---
Changes from RFC
- RFC: https://lore.kernel.org/[email protected]
- Drop RFC tag.
mm/damon/core.c | 2 ++ 1 file changed, 2 insertions(+)
mm/damon/core.c +2 -0
@@ -2883,6 +2883,8 @@ static void damos_adjust_quota(struct damon_ctx *c, struct damos *s)if (!quota->total_charged_sz && !quota->charged_from) { quota->charged_from = jiffies;damos_set_effective_quota (c, s); +if (trace_damos_esz_enabled ()) +damos_trace_esz (c, s, quota); }/* New charge window starts */
base-commit: 796dd9092b9c9d93dd48213582d45c43e93fa187
Signature · 1 line
2.47.3
Andrew Morton
maintainerQuoted 18 lines · On Wed, 20 May 2026 08:03:10 -0700 SeongJae Park <[email protected]> wrote:
DAMON traces effective size quota from the second update, only if a change has been made by the update. Tracing only changed updates was an intentional decision to avoid unnecessary same value tracing. Always skipping the first value is just an unintended mistake.
The mistake makes the tracepoint based investigation incomplete, because the first effective size quota is never traced. It is not a big issue when the 'consist' quota tuner is used, because it keeps changing the quota in the usual setup.
However, when the 'temporal' tuner is used, the quota value is not changed before the goal achievement status is completely changed. For example, if the DAMOS scheme is started with an under-achieved goal, the quota is set to the maximum value, and kept the same value until the goal is achieved. Because DAMON skips the first value, the user cannot know what effective quota the current scheme is using. Only after the goal is achieved, the effective quota is changed to zero, and traced.
Quoted 8 lines
Unconditionally trace the initial quota value to fix this problem.
Note that the 'temporal' quota tuner was introduced by commit
af738a6a00c1("mm/damon/core: introduceDAMOS_QUOTA_GOAL_TUNER_TEMPORAL"), which was added to 7.1-rc1. But even with the 'consist' quota tuner, the tracing is unintentionally incomplete. Hence this commit marks the introduction of the trace event as the broken commit.
OK, but...
Quoted 3 lines
Fixes a86d695193bf ("mm/damon: add trace event for effective size quota")Cc <[email protected]> # 6.17.xSigned-off-by SeongJae Park <[email protected]>
The patch is marked for backporting but it assumes the presence of "mm/damon/core: make charge_addr_from aware of end-address exclusivity", which is queued for 7.2-rc1.
We can either redo this against current -linus and fix up mm.git's "mm/damon/core: make charge_addr_from aware of end-address exclusivity" or we can queue this for 7.2-rc1 and you get to deal with fallout when -stable maintainers hit issues backporting this.
Preferences?
SeongJae Park
maintainerQuoted 39 lines · On Thu, 21 May 2026 16:28:34 -0700 Andrew Morton <[email protected]>…
Quoted 18 lines · On Wed, 20 May 2026 08:03:10 -0700 SeongJae Park <[email protected]> wrote:
DAMON traces effective size quota from the second update, only if a change has been made by the update. Tracing only changed updates was an intentional decision to avoid unnecessary same value tracing. Always skipping the first value is just an unintended mistake.
The mistake makes the tracepoint based investigation incomplete, because the first effective size quota is never traced. It is not a big issue when the 'consist' quota tuner is used, because it keeps changing the quota in the usual setup.
However, when the 'temporal' tuner is used, the quota value is not changed before the goal achievement status is completely changed. For example, if the DAMOS scheme is started with an under-achieved goal, the quota is set to the maximum value, and kept the same value until the goal is achieved. Because DAMON skips the first value, the user cannot know what effective quota the current scheme is using. Only after the goal is achieved, the effective quota is changed to zero, and traced.
Quoted 8 lines
Unconditionally trace the initial quota value to fix this problem.
Note that the 'temporal' quota tuner was introduced by commit
af738a6a00c1("mm/damon/core: introduceDAMOS_QUOTA_GOAL_TUNER_TEMPORAL"), which was added to 7.1-rc1. But even with the 'consist' quota tuner, the tracing is unintentionally incomplete. Hence this commit marks the introduction of the trace event as the broken commit.OK, but...
Quoted 3 lines
Fixes a86d695193bf ("mm/damon: add trace event for effective size quota")Cc <[email protected]> # 6.17.xSigned-off-by SeongJae Park <[email protected]>The patch is marked for backporting but it assumes the presence of "
mm/damon/core: makecharge_addr_fromaware of end-address exclusivity", which is queued for 7.2-rc1.
Quoted 6 lines
We can either redo this against current -linus and fix up mm.git's "
mm/damon/core: makecharge_addr_fromaware of end-address exclusivity" or we can queue this for 7.2-rc1 and you get to deal with fallout when -stable maintainers hit issues backporting this.Preferences?
Either is ok. Because this fix is not urgent to my perspective, I'd pick the second option. Let me know if you need anything from my side.
Thanks,
SJ
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