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 [off-list ref] wrote:

quoted

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@kernel.org

"
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.