On Sat, Sep 18, 2021 at 1:20 PM Barry Song [off-list ref] wrote:

On Sat, Sep 18, 2021 at 12:08 AM Muchun Song [off-list ref] wrote:

quoted

Since the head vmemmap page frame associated with each HugeTLB page is
reused, we should hide the PG_head flag of tail struct page from the
user. Add a tese case to check whether it is work properly.

TBH, I am a bit confused. I was thinking about some kernel unit tests to make
sure those kernel APIs touched by this patchset are still working as before.
This userspace test, while certainly useful for checking the content of page
frames as expected, doesn't directly prove things haven't changed.

In patch 1/4, a couple of APIs have the fixup for the fake head issue.
Do you think a test like the below would be more sensible?
1. alloc 2MB hugeTLB

It is done in main().

2. get each page frame
3. apply those APIs in each page frame
4. Those APIs work completely the same as before.

Reading the flags of a page by /proc/kpageflags is done
in stable_page_flags(), which has invoked PageHead(),
PageTail(), PageCompound() and compound_head().
If those APIs work properly, the head page must have
15 and 17 bits set. And tail pages must have 16 and 17
bits set but 15 unset.

So I think check_page_flags() has done the step 2 to 4.
What do you think?

Thanks.