Re: [PATCH v3] mm: huge_memory: a new debugfs interface for splitting THP tests.

[Kirill A. Shutemov]

On Thu, Mar 11, 2021 at 07:57:12PM -0500, Zi Yan wrote:
> From: Zi Yan <ziy@xxxxxxxxxx>
> 
> We do not have a direct user interface of splitting the compound page
> backing a THP

But we do. You expand it.

> and there is no need unless we want to expose the THP
> implementation details to users. Make <debugfs>/split_huge_pages accept
> a new command to do that.
> 
> By writing "<pid>,<vaddr_start>,<vaddr_end>" to
> <debugfs>/split_huge_pages, THPs within the given virtual address range
> from the process with the given pid are split. It is used to test
> split_huge_page function. In addition, a selftest program is added to
> tools/testing/selftests/vm to utilize the interface by splitting
> PMD THPs and PTE-mapped THPs.
> 

Okay, makes sense.

But it doesn't cover non-mapped THPs. tmpfs may have file backed by THP
that mapped nowhere. Do we want to cover this case too?

Maybe have PID:<pid>,<vaddr_start>,<vaddr_end> and
FILE:<path>,<off_start>,<off_end> ?

-- 
 Kirill A. Shutemov