Re: [Chapter One] THP zones: the use cases of policy zones

[Matthew Wilcox <willy@infradead.org>]

On Thu, Feb 29, 2024 at 11:34:33AM -0700, Yu Zhao wrote:
> Compared with the hugeTLB pool approach, THP zones tap into core MM
> features including:
> 1. THP allocations can fall back to the lower zones, which can have
>    higher latency but still succeed.
> 2. THPs can be either shattered (see Chapter Two) if partially
>    unmapped or reclaimed if becoming cold.
> 3. THP orders can be much smaller than the PMD/PUD orders, e.g., 64KB
>    contiguous PTEs on arm64 [1], which are more suitable for client
>    workloads.

Can this mechanism be used to fully replace the hugetlb pool approach?
That would be a major selling point.  It kind of feels like it should,
but I am insufficiently expert to be certain.

I'll read over the patches sometime soon.  There's a lot to go through.
Something I didn't see in the cover letter or commit messages was any
discussion of page->flags and how many bits we use for ZONE (particularly
on 32-bit).  Perhaps I'll discover the answer to that as I read.