On Thu, Apr 08, 2021 at 04:13:32PM -0700, Darrick J. Wong wrote: > On Wed, Apr 07, 2021 at 02:46:10PM -0700, Daniel Xu wrote: > > There currently does not exist a way to answer the question: "What is in > > the page cache?". There are various heuristics and counters but nothing > > that can tell you anything like: > > > > * 3M from /home/dxu/foo.txt > > * 5K from ... > > 5K? That's an extraordinary Weird Machine(tm). Just typing random numbers :) > > * etc. > > > > The answer to the question is particularly useful in the stacked > > container world. Stacked containers implies multiple containers are run > > on the same physical host. Memory is precious resource on some (if not > > most) of these systems. On these systems, it's useful to know how much > > duplicated data is in the page cache. Once you know the answer, you can > > do something about it. One possible technique would be bind mount common > > items from the root host into each container. > > Um, are you describing a system that uses BPF to deduplicating the page > cache by using bind mounts? Can the containers scribble on these files > and thereby mess up the other containers? What happens if the container > wants to update itself and clobbers the root host's copy instead? How > do you deal with a software update process failing because the root host > fights back against the container trying to change its files? No, the BPF progs are not intended to modify the pages. This is just for read only observability. > Also, I thought we weren't supposed to share resources across security > boundaries anymore? I can't speak to this, but bpf progs can pretty much be attached to anywhere so this iterator doesn't expose anything new. <...> Thanks, Daniel
