On Mon, Mar 15, 2021 at 12:07:39PM +0000, David Howells wrote: > > Hi Al, Miklós, > > Can we consider replacing the "insert cursor" approach we're currently > using for proc files to scan the current namespace's mount list[1] with > something that uses an xarray of mounts indexed by mnt_id? > > This has some advantages: > > (1) It's simpler. We don't need to insert dummy mount objects as > bookmarks into the mount list and code that's walking the list doesn't > have to carefully step over them. > > (2) We can use the file position to represent the mnt_id and can jump to > it directly - ie. using seek() to jump to a mount object by its ID. > > (3) It might make it easier to use RCU in future to dump mount entries > rather than having to take namespace_sem. xarray provides for the > possibility of tagging entries to say that they're viewable to avoid > dumping incomplete mount objects.
Usually one fully constructs the object, then inserts it into the XArray. > But there are a number of disadvantages: > > (1) We have to allocate memory to maintain the xarray, which becomes more > of a problem as mnt_id values get scattered. mnt_id values don't seem to get particularly scattered. They're allocated using an IDA, so they stay small (unlike someone using idr_alloc_cyclic ;-).
