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From:   SeongJae Park <sjpark@amazon.com>
To:     Andrew Morton <akpm@linux-foundation.org>
CC:     Minchan Kim <minchan@kernel.org>,
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        Michal Hocko <mhocko@suse.com>,
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        John Dias <joaodias@google.com>,
        Joel Fernandes <joel@joelfernandes.org>, <sj38.park@gmail.com>,
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Subject: Re: Re: [PATCH v6 0/7] introduce memory hinting API for external process
Date:   Thu, 20 Feb 2020 10:16:31 +0100
Message-ID: <20200220091631.31949-1-sjpark@amazon.com>
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On Wed, 19 Feb 2020 12:01:23 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:

> On Tue, 18 Feb 2020 17:44:26 -0800 Minchan Kim <minchan@kernel.org> 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?
> 
> 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/


Thanks,
SeongJae Park