On 12/06/18 14:36, Matthew Wilcox wrote: > On Tue, Jun 12, 2018 at 12:54:09PM +0300, Igor Stoppa wrote: [...] >> Although, in your case, you noticed a problem with userspace, while I do >> not care at all about that, so maybe there is some wriggling space there ... > > Yes; if your pages can never be mapped to userspace, then there's no > problem. Many other users of struct page use the page->mapping field > for other purposes. > >> Why not having a reference (either direct or indirect) to the actual >> vmap area, and then the flag there, instead? > > Because what we're trying to do is find out "Given a random struct page, > what is it used for". It might be page cache, it might be slab, it > might be anything. We can't go round randomly dereferencing pointers > and seeing what pot of gold is at the end of that rainbow. Ah, I had understood that it was already given that it was a vmalloc page. [...] > It might be useful to refer to the earlier patch which included that > information: > > https://www.spinics.net/lists/linux-mm/msg152818.html thank you, igor
