On Mon, Dec 17, 2018 at 03:55:01PM -0500, Jerome Glisse wrote: > On Mon, Dec 17, 2018 at 11:59:22AM -0800, Matthew Wilcox wrote: > > 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. > > And i have propose a way that do not need to ditch hmm_data nor > needs to remove page from the lru. What is it you do not like > with that ? I don't like bounce buffering. I don't like "end of writeback doesn't mark page as clean". I don't like pages being on the LRU that aren't actually removable. I don't like writing pages back which we know we're going to have to write back again.
