Re: [PATCH v6 0/7] introduce memory hinting API for external process

[Minchan Kim]

Hi Andrew,

On Wed, Feb 19, 2020 at 12:01:23PM -0800, Andrew Morton wrote:
> On Tue, 18 Feb 2020 17:44:26 -0800 Minchan Kim <minchan@xxxxxxxxxx> wrote:
> 
> > Now, we have MADV_PAGEOUT and MADV_COLD as madvise hinting API. With that,
> > application could give hints to kernel what memory range are preferred to be
> > reclaimed. However, in some platform(e.g., Android), the information
> > required to make the hinting decision is not known to the app.
> > Instead, it is known to a centralized userspace daemon(e.g., ActivityManagerService),
> > and that daemon must be able to initiate reclaim on its own without any app
> > involvement.
> > 
> 
> This patchset doesn't seem to be getting a lot of interest from other
> potential users?  It seems very specialized.  Are there or will there
> ever be any users of this apart from one Android daemon?


Quote from http://lkml.kernel.org/r/20190531064313.193437-1-minchan@xxxxxxxxxx

"
Brian Geffon in ChromeOS team had an experiment with process_madvise(2)
Quote form him:
"What I found is that by using process_madvise after a tab has been back
grounded for more than 45 seconds reduced the average tab switch times by
25%! This is a huge result and very obvious validation that process_madvise
hints works well for the ChromeOS use case."
"

> 
> Also, it doesn't terribly hard for ActivityManagerService to tell
> another process "now run madvise with these arguments".  Please explain
> why this is not practical in ActivityManagerService and also within
> other potential users of this syscall.

I think that's the almost a same question why ptrace doesn't work so
I summarizes the part in [2/7]:

* makes target task runnable creates memory layout change window so
 hiniting a wrong vma

* target task(e.g., background task) could live in little core with
  cpuset/group limited environment so we couldn't react quick enough,
  which causes more killing.


Thanks.