Re: [PATCH v5] binfmt_elf: Align eligible read-only PT_LOAD segments to PMD_SIZE for THP

[WANG Rui]

>> Thanks! Also adding Ryan who did the exec_folio_order() work for ARM,
>> and also raised good concerns in [1]
>>
>> The problem is not just alignment for elf, we need to fix more things like
>> mmap heuristics [2] and how unmapped areas are gotten [3].
>
> I agree, ideally, that would all be tackled in one go.

>From Usama’s v2 [1], it looks like we may be operating under slightly
different assumptions. His approach seems to key off page cache
characteristics when deciding segment alignment, while my patch is more
about proactively making things THP-friendly so that more code can end
up backed by large mappings. That helps in cases where a segment size is
just over a large mapping boundary.

Maybe what we really need here is to make sure the virtual address is
properly aligned, while avoiding overly aggressive alignment (e.g. capping
it at something like 32M, which is fairly common across architectures).
Beyond that, we can just leave it to THP in “always” mode. THP already has
its own heuristics to decide whether collapsing into large pages makes sense.

It also looks like this approach would work fine with Usama’s cont-pte
mappings. If so, would it make sense to implement [1] along these lines
instead?

[1] https://lore.kernel.org/linux-fsdevel/20260320140315.979307-4-usama.arif@xxxxxxxxx

Thanks,
Rui