Add support for memory swap settings for services by dperny · Pull Request #51114 · moby/moby

dperny · 2025-10-06T15:54:55Z

supersedes, closes Adding support for memory swap settings for services #37872
fixes Limiting SWAP usage in Swarm Mode? #34654
addresses [epic] add more options to service create / service update #25303

- What I did

Updated #37872 to the latest master branch.

- How I did it

Changed API version of the relevant settings to v1.52
Update various segments to deal with bit rot

- How to verify it

Comes with integration tests!

- Human readable description for the release notes

- Add support for memory swappiness in Swarm services.
  * `GET /services` now returns `SwapBytes` and `MemorySwappiness` fields as part of the `Resource` requirements.
  * `GET /services/{id}` now returns `SwapBytes` and `MemorySwappiness` fields as part of the `Resource` requirements.
  * `POST /services/create` now accepts `SwapBytes` and `MemorySwappiness` fields as part of the `Resource` requirements.
  * `POST /services/{id}/update` now accepts `SwapBytes` and `MemorySwappiness` fields as part of the `Resource` requirements.
  * `GET /tasks` now returns `SwapBytes` and `MemorySwappiness` fields as part of the `Resource` requirements.
  * `GET /tasks/{id}` now returns `SwapBytes` and `MemorySwappiness` fields as part of the `Resource` requirements.

dperny · 2025-10-06T15:55:17Z

Throwing this up as a draft for right now because I'm still dealing with the bit rot a bit.

dperny · 2025-10-08T14:53:14Z

Removed the section of integration tests which exec'd into the container to check that memory swappiness was actually set. If memory swappiness is set on the container config, we should trust that it is set on the container, and the test of that is a different test entirely.

dperny · 2025-10-09T18:03:51Z

This test passes locally on my machine, but fails in CI. I'm not sure why.

corhere · 2025-10-09T18:27:58Z

daemon/server/router/swarm/helpers.go

+		if service.TaskTemplate.Resources != nil {
+			if service.TaskTemplate.Resources.SwapBytes != nil {
+				// Setting services' swap size wasn't supported before
+				// API version 1.40


Suggested change

// API version 1.40

// API version 1.52

austinvazquez

Just a minor comment to touchup API v1.52 swagger as well.

api/swagger.yaml

thaJeztah · 2025-10-17T14:35:17Z

api/swagger.yaml

+            type: "integer"
+            format: "int64"


We probably should add that the minimum is -1, and add nullable and omit empty;

Suggested change

type: "integer"

format: "int64"

type: "integer"

format: "int64"

minimum: -1

x-nullable: true

x-omitempty: true

❓ ❓ ❓ do we need pointers though? Given that we have explicit -1 means "unset previous", would that already give enough information to distinguish "don't set" if the value is 0? (int-pointers can be finicky to deal with)

If a non-pointer value would work for us, we could change it, and remove the x-nullable;

Suggested change

type: "integer"

format: "int64"

type: "integer"

format: "int64"

minimum: -1

x-omitempty: true

In this case, -1 isn't "set default" it's "set unlimited". The null pointer is "set-default".

Ah, right, so

-1 means unlimited

nil means "default" (memory x 2 total)

0 means disable (no swap)

1 means 1 byte (or memory + 1 byte - I never know 😂) - 1 probably not an acceptable (or not a "sensible") value, but that's a separate topic 😂

thaJeztah · 2025-10-17T14:38:03Z

api/types/swarm/task.go

+	// Amount of swap in bytes - can only be used together with a memory limit
+	// -1 means unlimited
+	// a null pointer keeps the default behaviour of granting twice the memory
+	// amount in swap
+	SwapBytes *int64


Suggested change

// Amount of swap in bytes - can only be used together with a memory limit

// -1 means unlimited

// a null pointer keeps the default behaviour of granting twice the memory

// amount in swap

SwapBytes *int64

// Amount of swap in bytes - can only be used together with a memory limit

// -1 means unlimited. A null pointer keeps the default behaviour of granting

// twice the memory amount in swap.

SwapBytes *int64 `json:"SwapBytes,omitzero"`

Or (see my other comment)

Suggested change

// Amount of swap in bytes - can only be used together with a memory limit

// -1 means unlimited

// a null pointer keeps the default behaviour of granting twice the memory

// amount in swap

SwapBytes *int64

// Amount of swap in bytes - can only be used together with a memory limit

// -1 means unlimited. A zero value keeps the default behaviour of granting

// twice the memory amount in swap.

SwapBytes int64 `json:"SwapBytes,omitzero"`

thaJeztah · 2025-10-17T14:42:45Z

api/swagger.yaml

+            type: "integer"
+            format: "int64"


Suggested change

type: "integer"

format: "int64"

format: "int64"

minimum: -1

maximum: 100

x-nullable: true

x-omitempty: true

thaJeztah · 2025-10-17T14:43:45Z

api/types/swarm/task.go

+	// Tune container memory swappiness (0 to 100) - if not specified, defaults
+	// to the container OS's default - generally 60, or the value predefined in
+	// the image; set to -1 to unset a previously set value
+	MemorySwappiness *int64


Suggested change

MemorySwappiness *int64

MemorySwappiness *int64 `json:"MemorySwappiness,omitzero"`

Or (if we don't need a pointer)

Suggested change

MemorySwappiness *int64

MemorySwappiness int64 `json:"MemorySwappiness,omitzero"`

LOL, it could even be an int8, but from a quick look; looks like Swagger only knows about int32 and int64, so probably not worth changing?

thaJeztah · 2025-10-17T14:47:45Z

daemon/cluster/convert/service.go

 	return resources
 }

+func int64PointerFromGRPC(v *gogotypes.Int64Value) *int64 {


Unrelated to this PR, but wondering what our chances are to move away from gogo-protobuf; would it be possible?

It would be possible. It would not be pleasant.

thaJeztah · 2025-10-17T14:48:54Z

daemon/cluster/executor/container/container.go

+			} else if swapBytes >= 0 {
+				// resources.MemorySwap is actually the sum of the memory + the swap
+				resources.MemorySwap = resources.Memory + swapBytes


Ah, I guess this was the problem, so 0 is a valid value for this one? :sadpanda:

(if there's still a way to handle this without pointers, I'm still all ears though!)

☝️ I guess an explicit SwapEnable / SwapDisable could be an option for that, but not sure if we did elsewhere.

dperny · 2025-10-17T15:06:23Z

Updated with requested changes to swagger.yaml, v1.52.yaml, and the json annotations.

dperny · 2025-10-17T15:07:33Z

Solved the conflict in CHANGELOG.md

thaJeztah · 2025-10-17T15:48:22Z

daemon/server/router/swarm/helpers.go

+	if versions.LessThan(cliVersion, "1.52") {
+		if service.TaskTemplate.Resources != nil {
+			service.TaskTemplate.Resources.SwapBytes = nil
+			service.TaskTemplate.Resources.MemorySwappiness = nil
+		}
+	}


Unrelated, but I wonder if we ever described / documented the behavior when using an older client to update a service;

create service with (say) a v29 client, and set swap options

update service with (say) a v25 client

💥 swap options are gone

Don't know what a good solution is for that (other than versioning the spec with some schema version and returning warnings if features are set that are not supported in the API version)

This is the case with any of the settings gated behind the API version.

thaJeztah · 2025-10-17T19:29:49Z

OHMAN; before I forget and blame myself; I see there was a pending thing on the other PR; #37872 (comment)

swap should go into the Limits struct

and that in turns mean that Limits and Reservations are now going to be two separate structs
And all the changes that this entails.

And there was a related PR;

New iteration on structs for swap/swappiness swarmkit#2865

But I honestly forgot the details (it's been a while)

With integration tests Relevant Swarmkit PR: moby/swarmkit#2816 (updated the vendored version of Swarkit to that) Signed-off-by: Jean Rouge <[email protected]> Updated for latest master, fixed bitrot. Signed-off-by: Drew Erny <[email protected]>

dperny · 2025-10-20T15:34:51Z

I think it's not worthwhile to chase down the path proposed in the old PR -- the gains in cleanliness are outweighed by the increased scope of change.

thaJeztah

LGTM

github-actions bot added the module/api label Oct 6, 2025

dperny force-pushed the memory_flags_for_swarm branch 2 times, most recently from f0b5ae0 to 71fcf94 Compare October 7, 2025 17:04

corhere added area/api API kind/feature Functionality or other elements that the project doesn't currently have. Features are new and shiny impact/api impact/changelog area/swarm labels Oct 7, 2025

dperny force-pushed the memory_flags_for_swarm branch 10 times, most recently from 9ed391c to d71c18d Compare October 9, 2025 17:17

dperny force-pushed the memory_flags_for_swarm branch from d71c18d to e2158c7 Compare October 9, 2025 18:12

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dperny force-pushed the memory_flags_for_swarm branch 3 times, most recently from e33ae68 to cba4404 Compare October 13, 2025 15:10

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dperny force-pushed the memory_flags_for_swarm branch from cba4404 to c2e008c Compare October 17, 2025 14:59

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thaJeztah approved these changes Oct 23, 2025

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thaJeztah added the status/4-merge label Oct 23, 2025

vvoland merged commit ea59a8d into moby:master Oct 24, 2025
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thaJeztah mentioned this pull request Oct 24, 2025

integration/service: fix tests for updated client #51286

Merged

thaJeztah mentioned this pull request Dec 3, 2025

[epic] add more options to service create / service update #25303

Open

-            type: "integer"
-            format: "int64"
+            format: "int64"
+            minimum: -1
+            maximum: 100
+            x-nullable: true
+            x-omitempty: true

	MemorySwappiness *int64
	MemorySwappiness *int64 `json:"MemorySwappiness,omitzero"`

	MemorySwappiness *int64
	MemorySwappiness int64 `json:"MemorySwappiness,omitzero"`

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dperny commented Oct 6, 2025 •

edited by vvoland

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