Re: [RFC 7/7] mm: madvise support MADV_ANONYMOUS_FILTER and MADV_FILE_FILTER

[Minchan Kim]

On Tue, May 28, 2019 at 11:08:21AM +0200, Michal Hocko wrote:
> On Tue 28-05-19 17:49:27, Minchan Kim wrote:
> > On Tue, May 28, 2019 at 01:31:13AM -0700, Daniel Colascione wrote:
> > > On Tue, May 28, 2019 at 1:14 AM Minchan Kim <minchan@xxxxxxxxxx> wrote:
> > > > if we went with the per vma fd approach then you would get this
> > > > > feature automatically because map_files would refer to file backed
> > > > > mappings while map_anon could refer only to anonymous mappings.
> > > >
> > > > The reason to add such filter option is to avoid the parsing overhead
> > > > so map_anon wouldn't be helpful.
> > > 
> > > Without chiming on whether the filter option is a good idea, I'd like
> > > to suggest that providing an efficient binary interfaces for pulling
> > > memory map information out of processes.  Some single-system-call
> > > method for retrieving a binary snapshot of a process's address space
> > > complete with attributes (selectable, like statx?) for each VMA would
> > > reduce complexity and increase performance in a variety of areas,
> > > e.g., Android memory map debugging commands.
> > 
> > I agree it's the best we can get *generally*.
> > Michal, any opinion?
> 
> I am not really sure this is directly related. I think the primary
> question that we have to sort out first is whether we want to have
> the remote madvise call process or vma fd based. This is an important
> distinction wrt. usability. I have only seen pid vs. pidfd discussions
> so far unfortunately.

With current usecase, it's per-process API with distinguishable anon/file
but thought it could be easily extended later for each address range
operation as userspace getting smarter with more information.