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

On Wed, 19 Feb 2020 12:01:23 -0800 Andrew Morton [off-list ref] 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?

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 personally have interest in and hope successful development/merge of this
patchset.

The interested usecases of 'madvise_process()' for me is optimizations of
general memory-intensive workloads having dynamic data access patterns on
hierarchical memory systems (e.g., multi-tier memory or fast storage based swap
devices).  In more detail, I'm already using a part of this patchset for my RFC
patchset implementing Data Access Monitoring-based Operation Schemes[1].  For
my specific case, I don't need new system call but only target task argument,
though.

Once in a past, before joining my current company, I tried using 'madvise()' to
optimize some scientific HPC programs.  The improvement results were clear, but
optimizing each of the workloads was challenging and time-consuming.  I believe
this new systemcall to be very helpful for such cases, either.

[1] https://lore.kernel.org/linux-mm/20200218085309.18346-1-sjpark@amazon.com/ (local)


Thanks,
SeongJae Park