On Mon, Sep 21, 2020 at 04:53:38PM -0700, John Hubbard wrote:...
On 9/21/20 2:17 PM, Peter Xu wrote:
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 496c3ff97cce..6f291f8b74c6 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -441,6 +441,16 @@ struct mm_struct {
#endif
int map_count; /* number of VMAs */
+ /**
+ * @has_pinned: Whether this mm has pinned any pages. This can
+ * be either replaced in the future by @pinned_vm when it
+ * becomes stable, or grow into a counter on its own. We're
+ * aggresive on this bit now - even if the pinned pages were
+ * unpinned later on, we'll still keep this bit set for the
+ * lifecycle of this mm just for simplicity.
+ */
+ int has_pinned;
I think this would be elegant as an atomic_t, and using atomic_set() and
atomic_read(), which seem even more self-documenting that what you have here.
But it's admittedly a cosmetic point, combined with my perennial fear that
I'm missing something when I look at a READ_ONCE()/WRITE_ONCE() pair. :)
Yeah but I hope I'm using it right.. :) I used READ_ONCE/WRITE_ONCE explicitly
because I think they're cheaper than atomic operations, (which will, iiuc, lock
the bus).
It's completely OK to just ignore this comment, but I didn't want to completely
miss the opportunity to make it a tiny bit cleaner to the reader.
This can always become an atomic in the future, or am I wrong? Actually if
we're going to the counter way I feel like it's a must.