On 03.07.25 05:22, Sergey Senozhatsky wrote:
On (25/07/03 11:28), Sergey Senozhatsky wrote:
static int zs_page_migrate(struct page *newpage, struct page *page,
@@ -1736,6 +1736,13 @@ static int zs_page_migrate(struct page *newpage, struct
page *page,
unsigned long old_obj, new_obj;
unsigned int obj_idx;
+ /*
+ * TODO: nothing prevents a zspage from getting destroyed while
+ * isolated: we should disallow that and defer it.
+ */
Can you elaborate?
We can only free a zspage in free_zspage() while the page is locked.
After we isolated a zspage page for migration (under page lock!), we drop
^^ a physical page? (IOW zspage chain page?)
the lock again, to retake the lock when trying to migrate it.
That means, there is a window where a zspage can be freed although the page
is isolated for migration.
I see, thanks. Looks somewhat fragile. Is this a new thing?
No, it's been like that forever. And I was surprised that only zsmalloc
behaves that way
Oh, that makes two of us.
I sort of wonder if zs_page_migrate() VM_BUG_ON_PAGE() removal and
zspage check addition need to be landed outside of this series, as
a zsmalloc fixup.
Not sure if there is real value for that; given the review status, I
assume this series won't take too long to be ready for upstream. Of
course, if that is not the case we could try pulling them out.
--
Cheers,
David / dhildenb
