On Wed 07-08-19 19:36:37, Ira Weiny wrote: > On Wed, Aug 07, 2019 at 10:46:49AM +0200, Michal Hocko wrote: > > > So I think your debug option and my suggested renaming serve a bit > > > different purposes (and thus both make sense). If you do the renaming, you > > > can just grep to see unconverted sites. Also when someone merges new GUP > > > user (unaware of the new rules) while you switch GUP to use pins instead of > > > ordinary references, you'll get compilation error in case of renaming > > > instead of hard to debug refcount leak without the renaming. And such > > > conflict is almost bound to happen given the size of GUP patch set... Also > > > the renaming serves against the "coding inertia" - i.e., GUP is around for > > > ages so people just use it without checking any documentation or comments. > > > After switching how GUP works, what used to be correct isn't anymore so > > > renaming the function serves as a warning that something has really > > > changed. > > > > Fully agreed! > > Ok Prior to this I've been basing all my work for the RDMA/FS DAX stuff in > Johns put_user_pages()... (Including when I proposed failing truncate with a > lease in June [1]) > > However, based on the suggestions in that thread it became clear that a new > interface was going to need to be added to pass in the "RDMA file" information > to GUP to associate file pins with the correct processes... > > I have many drawings on my white board with "a whole lot of lines" on them to > make sure that if a process opens a file, mmaps it, pins it with RDMA, _closes_ > it, and ummaps it; that the resulting file pin can still be traced back to the > RDMA context and all the processes which may have access to it.... No matter > where the original context may have come from. I believe I have accomplished > that. > > Before I go on, I would like to say that the "imbalance" of get_user_pages() > and put_page() bothers me from a purist standpoint... However, since this > discussion cropped up I went ahead and ported my work to Linus' current master > (5.3-rc3+) and in doing so I only had to steal a bit of Johns code... Sorry > John... :-( > > I don't have the commit messages all cleaned up and I know there may be some > discussion on these new interfaces but I wanted to throw this series out there > because I think it may be what Jan and Michal are driving at (or at least in > that direction. > > Right now only RDMA and DAX FS's are supported. Other users of GUP will still > fail on a DAX file and regular files will still be at risk.[2] > > I've pushed this work (based 5.3-rc3+ (33920f1ec5bf)) here[3]: > > https://github.com/weiny2/linux-kernel/tree/linus-rdmafsdax-b0-v3 > > I think the most relevant patch to this conversation is: > > https://github.com/weiny2/linux-kernel/commit/5d377653ba5cf11c3b716f904b057bee6641aaf6 > > I stole Jans suggestion for a name as the name I used while prototyping was > pretty bad... So Thanks Jan... ;-) For your function, I'd choose a name like vaddr_pin_leased_pages() so that association with a lease is clear from the name :) Also I'd choose the counterpart to be vaddr_unpin_leased_page[s](). Especially having put_page in the name looks confusing to me... Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
