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fix: disable swap for executor_linux allocations #3958

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merged 2 commits into from
Mar 13, 2018
Merged

fix: disable swap for executor_linux allocations #3958

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fix: disable swap for executor_linux allocations
fho Mar 9, 2018
6c9dc48
Add #3958 to changelog
schmichael Mar 13, 2018
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,7 @@ BUG FIXES:
space in it on Windows [[GH-3855](https://github.com/hashicorp/nomad/issues/3855)]
* client/vault: Recognize renewing non-renewable Vault lease as fatal [[GH-3727](https://github.com/hashicorp/nomad/issues/3727)]
* config: Revert minimum CPU limit back to 20 from 100.
* driver/exec: Properly disable swapping [[GH-3958](https://github.com/hashicorp/nomad/issues/3958)]
* driver/lxc: Cleanup LXC containers after errors on container startup. [[GH-3773](https://github.com/hashicorp/nomad/issues/3773)]
* ui: Fix ui on non-leaders when ACLs are enabled [[GH-3722](https://github.com/hashicorp/nomad/issues/3722)]
* ui: Fix requests using client-side certificates in Firefox. [[GH-3728](https://github.com/hashicorp/nomad/pull/3728)]
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3 changes: 2 additions & 1 deletion client/driver/executor/executor_linux.go
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Expand Up @@ -83,7 +83,8 @@ func (e *UniversalExecutor) configureCgroups(resources *structs.Resources) error
// Total amount of memory allowed to consume
e.resConCtx.groups.Resources.Memory = int64(resources.MemoryMB * 1024 * 1024)
// Disable swap to avoid issues on the machine
e.resConCtx.groups.Resources.MemorySwap = int64(-1)
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Is there a reason to remove this? Is it possible that in some rare situations it may work while the swappiness approach may not?

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@fho fho Mar 13, 2018 •
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Is there a reason to remove this?

Yes

1.) Writing -1 to the memsw.limit_in_bytes file does not disable swap. It sets the limit to unlimited.

NOTE: We can write "-1" to reset the *.limit_in_bytes(unlimited).

https://www.kernel.org/doc/Documentation/cgroup-v1/memory.txt
I'll update my commit message accordingly.

2.) It's sufficient to disable swapping via a single mechanism.

Is it possible that in some rare situations it may work while the swappiness approach may not?

Not that I'm aware off. The swappiness value can be set when
CONFIG_MEMCG is enabled and the cggroup memory fs is mounted.
Both are also preconditions for enabling CONFIG_MEMCG_SWAP_ENABLED.

var memSwappiness int64 = 0
e.resConCtx.groups.Resources.MemorySwappiness = &memSwappiness
}

if resources.CPU < 2 {
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