On Tue, Jul 19, 2022 at 09:23:49PM +0100, Matthew Wilcox wrote: > On Tue, Jul 19, 2022 at 11:19:24AM +0200, Fabio M. De Francesco wrote: > > On martedì 19 luglio 2022 00:19:50 CEST Luis Chamberlain wrote: > > > > Therefore, replace kmap() with kmap_local_page(). > > > > > > While this churn is going on everywhere I was wondering why not > > > go ahead and adopt kmap_local_folio() instead? > > > > I'm sorry but, due to my lack of knowledge and experience, I'm not sure to > > understand how kmap_local_folio() could help here. My fault. I'm going to > > make some research and ask for help from more experienced developers. > > I haven't made this suggestion to Fabio before for a few reasons. > > First, it makes his work harder. He not only has to understand the > implications of the kmap semantic changes but also the implications of > the folio change. > > Then, I'm not sure that I necessarily have enough infrastructure in place > for doing a folio conversion everywhere that he's doing a kmap/kmap_atomic > to kmap_local_page conversion. > > What makes it particularly tricky is that you can only kmap a single > page out of a folio at a time; there's no ability to kmap the entire > folio, no matter how large it is. I've looked at doing the conversion > for ext2 directories, and it's _tricky_. There's only one 'checked' > flag for the entire folio, but ext2_check_page() needs to take a mapped > page. So now we have to make a judgement call about whether to support > caching ext2 directories with large folios or whether to restrict them > to single-page folios. > > So yes, there's probably a second patch coming for maintainers to look > at that will convert the kmap_local_page() to kmap_local_folio(). > However, I think it's actually less of a burden for maintainers if > these two different conversions happen separately because there are very > different considerations to review. Also, there's no equivalent to kmap() > or kmap_atomic() for folios (deliberately), so the more conversions to > kmap_local_page() Fabio gets done, the easier it will be for a later > folio conversion. Makes sense, thanks for the feedback. I'll wrestle with ensuring the first step to kmap_local_page() doens't break things where I see them suggested first. Luis
