On Thu, Feb 14, 2019 at 12:20:11PM -0800, Dan Williams wrote: > On Thu, Feb 14, 2019 at 12:09 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > > > On Thu, Feb 14, 2019 at 11:31:24AM -0800, Dan Williams wrote: > > > On Thu, Feb 14, 2019 at 11:10 AM Jerome Glisse <jglisse@xxxxxxxxxx> wrote: > > > > I am just again working on my struct page mapping patchset as well as > > > > the generic page write protection that sits on top. I hope to be able > > > > to post the v2 in couple weeks. You can always look at my posting last > > > > year to see more details. > > > > > > Yes, I have that in mind as one of the contenders. However, it's not > > > clear to me that its a suitable fit for filesystem-reflink. Others > > > have floated the 'page proxy' idea, so it would be good to discuss the > > > merits of the general approaches. > > > > ... and my preferred option of putting pfn entries in the page cache. > > Another option to include the discussion. > > > Or is that what you meant by "page proxy"? > > Page proxy would be an object that a filesystem could allocate to > point back to a single physical 'struct page *'. The proxy would > contain an override for page->index. Note that generic page write protection has such object, kind of like stable_node in KSM. You overwritte page->mapping to point to this generic struct which has a pointer to set of callback so that whatever is protecting the page can offer API to break protection (break sharing here). So instead of having struct proxy_page -> struct page you would have the reverse: struct page -> struct proxy and so you do not have to change much in all the file system beside removing the reliance on page->mapping which is what most of my patches are about. Cheers, Jérôme
