On Tue, Oct 04, 2022 at 03:40:36PM +0100, Matthew Wilcox wrote: > On Tue, Oct 04, 2022 at 11:26:33PM +0900, Hyeonggon Yoo wrote: > > > It's the acquisition of > > > the refcount which stabilises the slab flag, not holding the lock. > > > > But can you please elaborate how this prevents race between > > allocation & initialization of a slab and isolate_movable_page()? > > > > Or maybe we can handle it with frozen folio as Vlastimil suggested? ;-) > > Yes, we discussed that a little yesterday. I'm hoping to have a > refreshed patchset for frozen folios out today. Some of this patch > is still needed, even if we go that route. Good to hear that. With that, everyting looks sane to me. > > > @@ -91,8 +99,8 @@ int isolate_movable_page(struct page *page, isolate_mode_t mode) > > > * lets be sure we have the page lock > > > * before proceeding with the movable page isolation steps. > > > */ > > > - if (unlikely(!trylock_page(page))) > > > - goto out_putpage; > > > + if (unlikely(!folio_trylock(folio))) > > > + goto out_put; > > > > I don't know much about callers that this is trying to avoid race aginst... > > > > But for this to make sense, I think *every users* that doing their stuff with > > sub-page of a compound page should acquire folio lock and not page lock > > of sub-page, right? > > There is no page lock per se. If you try to acquire the lock on a tail > page, it acquires the lock on its head page. It's been that way for a > very long time. A lot of people are confused by this, which was part of > the motivation for making it explicit with folios. You are right! Reading the code, too bad I even assumed that there was sub-page lock. -- Thanks, Hyeonggon
