On Mon, Dec 17, 2018 at 02:54:08PM -0500, Jerome Glisse wrote: > On Mon, Dec 17, 2018 at 11:51:51AM -0800, Matthew Wilcox wrote: > > On Mon, Dec 17, 2018 at 02:48:00PM -0500, Jerome Glisse wrote: > > > On Mon, Dec 17, 2018 at 10:34:43AM -0800, Matthew Wilcox wrote: > > > > No. The solution John, Dan & I have been looking at is to take the > > > > dirty page off the LRU while it is pinned by GUP. It will never be > > > > found for writeback. > > > > > > With the solution you are proposing we loose GUP fast and we have to > > > allocate a structure for each page that is under GUP, and the LRU > > > changes too. Moreover by not writing back there is a greater chance > > > of data loss. > > > > Why can't you store the hmm_data in a side data structure? Why does it > > have to be in struct page? > > hmm_data is not even the issue here, we can have a pincount without > moving things around. So i do not see the need to complexify any of > the existing code to add new structure and consume more memory for > no good reasons. I do not see any benefit in that. You said "we have to allocate a structure for each page that is under GUP". The only reason to do that is if we want to keep hmm_data in struct page. If we ditch hmm_data, there's no need to allocate a structure, and we don't lose GUP fast either.
