On 8/25/21 00:08, Mike Kravetz wrote:

Add Vlastimil and Hillf,

Well, I set up a test environment on a larger system to get some
numbers.  My 'load' on the system was filling the page cache with
clean pages.  The thought is that these pages could easily be reclaimed.

When trying to get numbers I hit a hugetlb page allocation stall where
__alloc_pages(__GFP_RETRY_MAYFAIL, order 9) would stall forever (or at
least an hour).  It was very much like the symptoms addressed here:
https://lore.kernel.org/linux-mm/20190806014744.15446-1-mike.kravetz@oracle.com/ (local)

This was on 5.14.0-rc6-next-20210820.

I'll do some more digging as this appears to be some dark corner case of
reclaim and/or compaction.  The 'good news' is that I can reproduce
this.

Interesting, let's see if that's some kind of new regression.

quoted

And the second problem would benefit from some words to help us
understand how much real-world hurt this causes, and how frequently.
And let's understand what the userspace workarounds look like, etc.

The stall above was from doing a simple 'free 1GB page' followed by
'allocate 512 MB pages' from userspace.

Is the allocation different in any way than the usual hugepage allocation
possible today?

Getting out another version of this series will be delayed, as I think
we need to address or understand this issue first.