RFC: malloc automatic THP opt-in breaks madvise contract for container hosts
Project / Subsystem
glibc / malloc
Date
2026-04-17
Proposer
Sun, Yutong <[email protected]>
Source type
public_inbox
Consensus
Proposed
Sentiment
4/10
Technical tradeoffs
- • Automatic THP allocation can be beneficial for some workloads but detrimental in container environments.
- • Using GLIBC_TUNABLES is not a stable ABI.
- • Disabling THP system-wide penalizes workloads that benefit from it.
All attributes
- project
- glibc
- subsystem
- malloc
- patch_id
- —
- discussion_id
- [email protected]
- source_type
- public_inbox
- title
- RFC: malloc automatic THP opt-in breaks madvise contract for container hosts
- headline
- Automatic THP in malloc breaks madvise for container hosts
- tldr
- Glibc's automatic THP opt-in via madvise hurts container hosts by allocating huge pages to small management processes instead of actual workloads.
- stakes
- Unexpected THP usage can degrade performance in containerized environments, wasting memory on shims instead of benefiting the intended applications.
- proposer
- Sun, Yutong <[email protected]>
- consensus
- Proposed
- outcome
- proposed
- sentiment_score
- 4
- sentiment_rationale
- The RFC identifies a performance regression in a specific use case (container hosts), which can lead to contention.
- technical_tradeoffs
-
- • Automatic THP allocation can be beneficial for some workloads but detrimental in container environments.
- • Using GLIBC_TUNABLES is not a stable ABI.
- • Disabling THP system-wide penalizes workloads that benefit from it.
- series_id
- —
- series_role
- standalone
- series_parts
- []
- tags
-
- • malloc
- • THP
- • containers
- • performance
- • madvise
- bugzilla_url
- —
- date
- 2026-04-17T00:00:00.000Z
RFC: malloc automatic THP opt-in breaks madvise contract for container hosts
Yutong Sun raises concerns about glibc’s automatic Transparent Huge Pages (THP) opt-in behavior via madvise(MADV_HUGEPAGE) for heap allocations. This breaks the intended semantics of madvise mode where applications explicitly opt-in. On container hosts, this leads to small management processes (container shims) receiving huge page allocations, while actual container workloads do not, wasting memory. The author proposes either reverting the change or making THP usage opt-in.