On (25/07/02 12:55), David Hildenbrand wrote: > On 02.07.25 12:10, Sergey Senozhatsky wrote: > > On (25/07/02 10:25), David Hildenbrand wrote: > > > On 02.07.25 10:11, Sergey Senozhatsky wrote: > > > > On (25/06/30 14:59), David Hildenbrand 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. > > > While we currently keep that working (as far as I can see), in the future > > > we > > > want to remove that support from the core. > > > > Maybe comment can more explicitly distinguish zspage isolation and > > physical page (zspage chain) isolation? zspages can get isolated > > for compaction (defragmentation), for instance, which is a different > > form of isolation. > > Well, it's confusing, as we have MM compaction (-> migration) and apparently > zs_compact. True. > I'll try to clarify that we are talking about isolation for page migration > purposes. Thanks.
