On Mon, Feb 7, 2022 at 7:32 AM David Hildenbrand <david@xxxxxxxxxx> wrote: > > Just like clearrefs, this can race against GUP-fast to detect pinned > pages. And just like clearrefs, we're not handling PMDs properly. And > just like anything that write-protects random anon pages right now, this > does not consider O_DIRECT as is. > > Fortunately, there are not too many users of clearreefs/softdirty > tracking out there (my search a while ago returned no open source > users). My assumption is that your feature might see more widespread use. > > Adding more random write protection until we fixed the COW issues [1] > really makes my stomach hurt on a Monday morning. I was not aware of these issues. > Please, let's defer any more features that rely on write-protecting > random anon pages until we have ways in place to not corrupt random user > space. > > That is: > 1) Teaching the COW logic to not copy pages that are pinned -- I'm > working on that. > 2) Converting O_DIRECT to use FOLL_PIN instead of FOLL_GET. John is > working on that. > > So I'm not against this change. I'm against this change at this point in > time. I agree. I will wait until the COW problems are solved to send this patch. -- Atenciosamente, Pedro Demarchi Gomes.
