On 16/04/19 22:12, Dan Williams wrote: > On Tue, Apr 16, 2019 at 11:59 AM Kent Overstreet > <kent.overstreet@xxxxxxxxx> wrote: <> > This all reminds of the failed attempt to teach the block layer to > operate without pages: > > https://lore.kernel.org/lkml/20150316201640.33102.33761.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > Exactly why I want to make sure it is just a [pointer | flag] and not any kind of pfn type. Let us please not go there again? >> >> Question though - why do we need a flag for whether a page is a GUP page or not? >> Couldn't the needed information just be determined by what range the pfn is not >> (i.e. whether or not it has a struct page associated with it)? > > That amounts to a pfn_valid() check which is a bit heavier than if we > can store a flag in the bv_pfn entry directly. > > I'd say create a new PFN_* flag, and make bv_pfn a 'pfn_t' rather than > an 'unsigned long'. > No, please please not. This is not a pfn and not a pfn_t. It is a page-ptr and a flag that says where/how to put_page it. IE I did a GUP on this page please do a PUP on this page instead of regular put_page. So no where do I mean pfn or pfn_t in this code. Then why? > That said, I'm still in favor of Jan's proposal to just make the > bv_page semantics uniform. Otherwise we're complicating this core > infrastructure for some yet to be implemented GPU memory management > capabilities with yet to be determined value. Circle back when that > value is clear, but in the meantime fix the GUP bug. > I agree there are simpler ways to solve the bugs at hand then to system wide separate get_user_page from get_page and force all put_user callers to remember what to do. Is there some Document explaining the all design of where this is going? Thanks Boaz
