linux-kernel - Re: [RFC 7/7] mm: madvise support MADV_ANONYMOUS_FILTER and MADV_FILE

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Date:   Tue, 28 May 2019 19:32:56 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Daniel Colascione <dancol@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Tim Murray <timmurray@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Brian Geffon <bgeffon@...gle.com>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [RFC 7/7] mm: madvise support MADV_ANONYMOUS_FILTER and
 MADV_FILE_FILTER

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@...nel.org> 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.