Re: [v6 05/15] mm: don't accessed uninitialized struct pages

From: Pasha Tatashin
Date: Mon Aug 14 2017 - 09:52:43 EST


mem_init()
free_all_bootmem()
free_low_memory_core_early()
for_each_reserved_mem_region()
reserve_bootmem_region()
init_reserved_page() <- if this is deferred reserved page
__init_single_pfn()
__init_single_page()

So, currently, we are using the value of page->flags to figure out if this
page has been initialized while being part of deferred page, but this is not
going to work for this project, as we do not zero the memory that is backing
the struct pages, and size the value of page->flags can be anything.

True, this is the initialization part I've missed in one of the previous
patches already. Would it be possible to only iterate over !reserved
memory blocks instead? Now that we discard all the metadata later it
should be quite easy to do for_each_memblock_type, no?

Hi Michal,

Clever suggestion to add a new iterator to go through unreserved existing memory, I do not think there is this iterator available, so it would need to be implemented, using similar approach to what I have done with a call back.

However, there is a different reason, why I took this current approach.

Daniel Jordan is working on a ktask support:
https://lkml.org/lkml/2017/7/14/666

He and I discussed on how to multi-thread struct pages initialization within memory nodes using ktasks. Having this callback interface makes that multi-threading quiet easy, improving the boot performance further, with his prototype we saw x4-6 improvements (using 4-8 threads per node). Reducing the total time it takes to initialize all struct pages on machines with terabytes of memory to less than one second.

Pasha