linux-kernel - Re: A noobish question on mm

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Message-ID: <CAFNq8R5q7=wx6WgDwYUrgntMfewHEU=YHTCG4CZp3JcYZsCzhw@mail.gmail.com>
Date:	Tue, 19 Feb 2013 14:38:03 +0800
From:	Li Haifeng <omycle@...il.com>
To:	Soham Chakraborty <sohamwonderpiku4u@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-mm@...ck.org
Subject: Re: A noobish question on mm

2013/2/19 Soham Chakraborty <sohamwonderpiku4u@...il.com>:
> Hey dude,
>
> Apologies for this kind of approach but I was not sure whether I can
> directly mail the list with such a noobish question. I have been poking
> around in mm subsystem for around 2 years now and I have never got a fine,
> bullet proof answer to this question.
>
> Why would something swap even if there is free or cached memory available.

It's known that swap operation is done with memory reclaiming.There
are three occasions for memory reclaiming: low on memory reclaiming,
Hibernation reclaiming, periodic reclaiming.

For periodic reclaiming, some page may be swapped out even if there is
free or cached memory available.

Please correct me if my understanding is wrong.

Regards,
Haifeng Li
>
> I have read about all possible theories including lru algorithm,
> vm.swappiness, kernel heuristics, overcommit of memory and all. But I for
> the heck of me, can't understand what is the issue. And I can't make the end
> users satisfied too. I keep blabbering kernel heuristics too much.
>
> Do you have any answer to this question. If you think this is worthy of
> going to list, I will surely do so.
>
> Soham
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