Re: transfer physical memory page to swap disk

From: Anupam Kapoor <anupam.kapoor@gmail.com>
To: "Valdis Klētnieks" <valdis.kletnieks@vt.edu>
Cc: Sumit Kumar <sumit686215@gmail.com>,
	kernelnewbies <kernelnewbies@kernelnewbies.org>
Subject: Re: transfer physical memory page to swap disk
Date: Sun, 19 Jan 2020 10:55:44 +0000	[thread overview]
Message-ID: <CAEXHiZEBpf2KKFQ04wUkQqoW809aSq+2SMfuLfvEkJswzBnGZQ@mail.gmail.com> (raw)
In-Reply-To: <412530.1579360214@turing-police>

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On Wed, 15 Jan 2020 18:23:05 +0530, Anupam Kapoor said:
>> On Wed, 15 Jan 2020 at 6:02 PM Sumit Kumar <sumit686215@gmail.com> wrote:
>>> Does C/C++ provide any API / system call that enables user to force the
>>> application to transfer some its physical pages to swap disk ? If so,
is it
>>> also possible to obtain the least used page using some API ?

>> would madvise not serve your needs ?

> There's this word "force" in the question.

> The problem is that madvise() is *advice* to the kernel, not a strict
> guarantee.  There's a difference between "If you need to move pages
> to disk, consider these pages first" and "Move them to disk now, whether
> you really wanted to or not".

ofcourse (afaik) there is no way for the application to force the
*kernel* to do something like this.

but if _all_ that is required is randomly unmapping some marked
application pages, _that_ can be naively 'done' by the application
itself :)

for example, have a list of unmappable pages and an unmapper thread
which does the unmapping for you (picking any element in the list
at random)

--
kind regards
anupam

In the beginning was the lambda, and the lambda was with Emacs, and Emacs
was the lambda.

On Sat, Jan 18, 2020 at 3:10 PM Valdis Klētnieks <valdis.kletnieks@vt.edu>
wrote:

> On Wed, 15 Jan 2020 18:23:05 +0530, Anupam Kapoor said:
> > On Wed, 15 Jan 2020 at 6:02 PM Sumit Kumar <sumit686215@gmail.com>
> wrote:
> > > Does C/C++ provide any API / system call that enables user to force the
> > > application to transfer some its physical pages to swap disk ? If so,
> is it
> > > also possible to obtain the least used page using some API ?
> > would madvise not serve your needs ?
>
> There's this word "force" in the question.
>
> The problem is that madvise() is *advice* to the kernel, not a strict
> guarantee.  There's a difference between "If you need to move pages
> to disk, consider these pages first" and "Move them to disk now, whether
> you really wanted to or not".
>
>

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