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From: Michal Hocko <mhocko@kernel.org>
To: Minchan Kim <minchan@kernel.org>
Cc: sspatil@google.com, kirill@shutemov.name,
	akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, linux-api@vger.kernel.org,
	oleksandr@redhat.com, surenb@google.com, timmurray@google.com,
	dancol@google.com, sonnyrao@google.com, bgeffon@google.com,
	hannes@cmpxchg.org, shakeelb@google.com, joaodias@google.com,
	ktkhai@virtuozzo.com, christian.brauner@ubuntu.com,
	sjpark@amazon.de
Subject: Re: [PATCH v2 2/5] mm: introduce external memory hinting API
Date: Wed, 22 Jan 2020 09:28:53 +0100	[thread overview]
Message-ID: <20200122082853.GS29276@dhcp22.suse.cz> (raw)
In-Reply-To: <20200121183212.GF140922@google.com>

On Tue 21-01-20 10:32:12, Minchan Kim wrote:
> On Mon, Jan 20, 2020 at 08:58:25AM +0100, Michal Hocko wrote:
[...]
> > The interface really has to be robust to future potential usecases.
> 
> I do understand your concern but for me, it's chicken and egg problem.
> We usually do best effort to make something perfect as far as possible
> but we also don't do over-engineering without real usecase from the
> beginning.
> 
> I already told you how we could synchronize among processes and potential
> way to be extended Daniel suggested(That's why current API has extra field
> for the cookie) even though we don't need it right now.

If you can synchronize with the target task then you do not need a
remote interface. Just use ptrace and you are done with it.

> If you want to suggest the other way, please explain why your idea is
> better and why we need it at this moment.

I believe I have explained my concerns and why they matter. All you are
saying is that you do not care because your particular usecase doesn't
care. And that is a first signal of a future disaster when we end up
with a broken and unfixable interface we have to maintain for ever.

I will not go as far as to nack this but you should seriously think
about other potential usecases and how they would work and what we are
going to do when a first non-cooperative userspace memory management
usecase materializes.
-- 
Michal Hocko
SUSE Labs

WARNING: multiple messages have this Message-ID (diff)
From: Michal Hocko <mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
To: Minchan Kim <minchan-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: sspatil-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org,
	kirill-oKw7cIdHH8eLwutG50LtGA@public.gmane.org,
	akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org,
	linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	oleksandr-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org,
	surenb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org,
	timmurray-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org,
	dancol-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org,
	sonnyrao-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org,
	bgeffon-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org,
	hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org,
	shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org,
	joaodias-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org,
	ktkhai-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org,
	christian.brauner-GeWIH/nMZzLQT0dZR+AlfA@public.gmane.org,
	sjpark-ebkRAfMGSJGzQB+pC5nmwQ@public.gmane.org
Subject: Re: [PATCH v2 2/5] mm: introduce external memory hinting API
Date: Wed, 22 Jan 2020 09:28:53 +0100	[thread overview]
Message-ID: <20200122082853.GS29276@dhcp22.suse.cz> (raw)
In-Reply-To: <20200121183212.GF140922-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>

On Tue 21-01-20 10:32:12, Minchan Kim wrote:
> On Mon, Jan 20, 2020 at 08:58:25AM +0100, Michal Hocko wrote:
[...]
> > The interface really has to be robust to future potential usecases.
> 
> I do understand your concern but for me, it's chicken and egg problem.
> We usually do best effort to make something perfect as far as possible
> but we also don't do over-engineering without real usecase from the
> beginning.
> 
> I already told you how we could synchronize among processes and potential
> way to be extended Daniel suggested(That's why current API has extra field
> for the cookie) even though we don't need it right now.

If you can synchronize with the target task then you do not need a
remote interface. Just use ptrace and you are done with it.

> If you want to suggest the other way, please explain why your idea is
> better and why we need it at this moment.

I believe I have explained my concerns and why they matter. All you are
saying is that you do not care because your particular usecase doesn't
care. And that is a first signal of a future disaster when we end up
with a broken and unfixable interface we have to maintain for ever.

I will not go as far as to nack this but you should seriously think
about other potential usecases and how they would work and what we are
going to do when a first non-cooperative userspace memory management
usecase materializes.
-- 
Michal Hocko
SUSE Labs

  reply	other threads:[~2020-01-22  8:28 UTC|newest]

Thread overview: 65+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-16 23:59 [PATCH v2 0/5] introduce memory hinting API for external process Minchan Kim
2020-01-16 23:59 ` [PATCH v2 1/5] mm: factor out madvise's core functionality Minchan Kim
2020-01-17 10:02   ` Kirill Tkhai
2020-01-17 10:02     ` Kirill Tkhai
2020-01-17 18:14     ` Minchan Kim
2020-01-17 18:14       ` Minchan Kim
2020-01-16 23:59 ` [PATCH v2 2/5] mm: introduce external memory hinting API Minchan Kim
2020-01-16 23:59   ` Minchan Kim
2020-01-17 11:52   ` Michal Hocko
2020-01-17 11:52     ` Michal Hocko
2020-01-17 15:58     ` Kirill A. Shutemov
2020-01-17 15:58       ` Kirill A. Shutemov
2020-01-17 17:32       ` Minchan Kim
2020-01-17 17:32         ` Minchan Kim
2020-01-17 21:26         ` Kirill A. Shutemov
2020-01-17 21:26           ` Kirill A. Shutemov
2020-01-18  9:40           ` SeongJae Park
2020-01-18  9:40             ` SeongJae Park
2020-01-19 16:14           ` sspatil
2020-01-19 16:14             ` sspatil-hpIqsD4AKlfQT0dZR+AlfA
2020-01-20  7:58             ` Michal Hocko
2020-01-20 10:39               ` Kirill Tkhai
2020-01-20 10:39                 ` Kirill Tkhai
2020-01-21 18:32               ` Minchan Kim
2020-01-22  8:28                 ` Michal Hocko [this message]
2020-01-22  8:28                   ` Michal Hocko
2020-01-22  9:36                   ` SeongJae Park
2020-01-22  9:36                     ` SeongJae Park
2020-01-22 10:02                     ` Michal Hocko
2020-01-22 10:02                       ` Michal Hocko
2020-01-22 13:28                       ` SeongJae Park
2020-01-22 13:28                         ` SeongJae Park
2020-01-23  1:41                   ` Minchan Kim
2020-01-23  1:41                     ` Minchan Kim
2020-01-23  9:13                     ` Michal Hocko
2020-01-21 18:11           ` Minchan Kim
2020-01-21 18:11             ` Minchan Kim
2020-01-22 10:44             ` Oleksandr Natalenko
2020-01-23  1:43               ` Minchan Kim
2020-01-23  7:29                 ` Oleksandr Natalenko
2020-01-17 17:25     ` Minchan Kim
2020-01-17 17:25       ` Minchan Kim
2020-01-20  8:03       ` Michal Hocko
2020-01-20  8:03         ` Michal Hocko
2020-01-20 10:24     ` Kirill Tkhai
2020-01-20 10:24       ` Kirill Tkhai
2020-01-20 11:27       ` Michal Hocko
2020-01-20 11:27         ` Michal Hocko
2020-01-20 12:39         ` Kirill A. Shutemov
2020-01-20 13:24           ` Michal Hocko
2020-01-20 13:24             ` Michal Hocko
2020-01-20 14:21             ` Kirill A. Shutemov
2020-01-20 15:44               ` Michal Hocko
2020-01-20 15:44                 ` Michal Hocko
2020-01-21 18:43             ` Minchan Kim
2020-01-21 18:43               ` Minchan Kim
2020-01-16 23:59 ` [PATCH v2 3/5] mm/madvise: employ mmget_still_valid for write lock Minchan Kim
2020-01-16 23:59 ` [PATCH v2 4/5] mm/madvise: allow KSM hints for remote API Minchan Kim
2020-01-17 10:13   ` Kirill Tkhai
2020-01-17 10:13     ` Kirill Tkhai
2020-01-17 12:34     ` Oleksandr Natalenko
2020-01-17 12:34       ` Oleksandr Natalenko
2020-01-21 17:45       ` Minchan Kim
2020-01-21 17:45         ` Minchan Kim
2020-01-16 23:59 ` [PATCH v2 5/5] mm: support both pid and pidfd for process_madvise Minchan Kim

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