On Thu, Jun 8, 2023 at 3:05 AM Lokesh Gidra <lokeshgidra@xxxxxxxxxx> wrote: > > On Tue, Jun 6, 2023 at 4:18 PM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > > > > On Tue, Jun 6, 2023 at 1:15 PM Vlastimil Babka <vbabka@xxxxxxx> wrote: > > > > > > On 4/13/23 17:36, Peter Xu wrote: > > > > On Thu, Apr 13, 2023 at 10:10:44AM +0200, David Hildenbrand wrote: > > > >> So instead, we consider the whole address space as a virtual, anon file, > > > >> starting at offset 0. The pgoff of a VMA is then simply the offset in that > > > >> virtual file (easily computed from the start of the VMA), and VMA merging is > > > >> just the same as for an ordinary file. > > > > > > > > Interesting point, thanks! > > > > > > FYI, I've advised a master thesis exploring how to update page->index during > > > mremap() to keep things mergeable: > > > > > > https://dspace.cuni.cz/bitstream/handle/20.500.11956/176288/120426800.pdf > > > > > > I think the last RFC posting was: > > > https://lore.kernel.org/all/20220516125405.1675-1-matenajakub@xxxxxxxxx/ > > > > > > It was really tricky for the general case. Maybe it would be more feasible > > > for the limited case Lokesh describes, if we could be sure the pages that > > > are moved aren't mapped anywhere else. > > It's great that mremap is being improved for mereabilitly. However, > IIUC, it would still cause unnecessary splits and merges in the > private anonymous case. Also, mremap works with mmap_sem exclusively > held, thereby impacting scalability of concurrent mremap calls. > > IMHO, Andrea's userfaultfd REMAP patch is a better alternative as it > doesn't have these downsides. > > > > > Lokesh asked me to pick up this work and prepare patches for > > upstreaming. I'll start working on them after I finish with per-vma > > lock support for swap and userfaultd (targeting later this week). > > Thanks for all the input folks! > > Thanks so much, Suren! I just posted the patchset at https://lore.kernel.org/all/20230914152620.2743033-1-surenb@xxxxxxxxxx/. I tried to keep it as true to Andrea's original as possible but still had to make some sizable changes, which I described in the cover letter. Feedback would be much appreciated!
