On 2025/1/8 18:52, Anshuman Khandual wrote:
I found another bug, that even for early section, when vmemmap_populate is called, SECTION_IS_EARLY is not set. Therefore, early_section() always return false.
Hmm, well that's unexpected.
Since vmemmap_populate() occurs during section initialization, it may be hard to say it is a bug..
However, should we instead using SECTION_MARKED_PRESENT to check? I tested well in my setup.
Hot plug flow:
1. section_activate -> vmemmap_populate
2. mark PRESENT
In contrast, the early flow:
1. memblocks_present -> mark PRESENT
2. __populate_section_memmap -> vmemmap_populate
But from a semantics perspective, should SECTION_MARKED_PRESENT be marked on a
section before SECTION_IS_EARLY ? Is it really the expected behaviour here or
that needs to be fixed first ?
The tricky part is vmemmap_populate initializes mem_map, that happens
during mem_section initialization process. PRESENT or EARLY tag is in
the same process as well. There doesn't appear to be a compelling reason
to enforce a specific sequence..
Although SYSTEM_BOOTING state check might help but section flag seems to be the
right thing to do here.
Good idea, I prefer to vote for this alternative rather than PRESENT
tag. As I see we already took this stage to determine whether memmap
pages are boot pages or not in common mm code:
https://elixir.bootlin.com/linux/v6.13-rc3/source/mm/sparse-vmemmap.c#L465
Would like to hear Catalin's perspective ?:)
