Re: [PATCH v5 18/22] docs: add documentation for memfd preservation via LUO

Pratyush Yadav
2025-11-13T17:00:02Z

On Thu, Nov 13 2025, Pasha Tatashin wrote:

>> +Limitations
>> +===========
>> +
>> +The current implementation has the following limitations:
>> +
>> +Size
>> + Currently the size of the file is limited by the size of the FDT. The FDT can
>> + be at of most ``MAX_PAGE_ORDER`` order. By default this is 4 MiB with 4K
>> + pages. Each page in the file is tracked using 16 bytes. This limits the
>> + maximum size of the file to 1 GiB.
>
> The above should be removed, as we are using KHO vmalloc that resolves
> this limitation. Pratyush, I suggest for v6 let's move memfd
> documnetation right into the code: memfd_luo.c and
> liveupdate/abi/memfd.h, and source it from there.

ACK. I think the section on behavior in different phases is also out of
date now, and the serialization format too. The format is more
accurately defined in include/linux/liveupdate/abi/memfd.h. So this
documentation needs an overhaul.

I don't mind moving it to the code and including it in the HTML docs via
kernel-doc. Will do that for the next revision.

>
> Keeping documentation with the code helps reduce code/doc divergence.
>
> Pasha

--
Regards,
Pratyush Yadav