RFC: malloc automatic THP opt-in breaks madvise contract for container hosts

[H.J. Lu]

On Fri, Apr 17, 2026 at 1:25 PM Sun, Yutong <yutongsu@amazon.com> wrote:
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> On 4/16/26, 10:23 PM, "Sun, Yutong" <yutongsu@amazon.com <mailto:yutongsu@amazon.com>> wrote:
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> Thanks for the pointer. The per-binary opt-in idea is interesting.
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> To clarify our case — the issue is specifically malloc's thp_init()
> auto-calling madvise(MADV_HUGEPAGE) when the kernel is in `madvise`
> mode. Your proposal covers PT_LOAD segments which seems broader.
> Would a binary without the property effectively get no THP at all
> under `madvise` mode?

My proposal is specific to THP usage on read-only segments.   THP usage
in malloc isn't impacted.   A different bit is needed for malloc.   One question
is if malloc THP usage should be opt-in or opt-out.   If THP usage in malloc
improves performance for majority cases, it should be opt-out.

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> Also, are you hearing similar reports from other distros as 2.43 rolls out?

No.  Yours is the first one I heard.  But I am not surprised, given
its side effects.

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> Again, as I mentioned we're carrying a revert patch [1] for now and happy to move to
> whatever upstream solution lands.
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-- 
H.J.