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.
