Hi Carlo,
On 27/03/2024 11:10, Carlo Nonato wrote:
Hi guys,
Question is: How would you justify such a change? IOW I'm not convinced
(yet) this wants doing there.
You mean in this series?
Looking at the code, the flag is originally set in
alloc_domheap_pages(). So I guess it would make sense to do it in
free_domheap_pages().
We don't hold the heap_lock there.
Regardless of the safety question (I will answer below), count_info is
not meant to be protected by heap_lock. The lock is protecting the heap
and ensure we are not corrupting them when there are concurrent call to
free_heap_pages().
> Is it safe to change count_info without it?
count_info is meant to be accessed locklessly. The flag PGC_extra cannot
be set/clear concurrently because you can't allocate a page that has not
yet been freed.
So it would be fine to use clear_bit(..., ...);
Cheers,
--
Julien Grall
