From: valdis.kletnieks@vt.edu (valdis.kletnieks at vt.edu)
To: kernelnewbies@lists.kernelnewbies.org
Subject: a question on mapping from PTE to swap entry
Date: Thu, 15 Nov 2018 12:59:52 -0500 [thread overview]
Message-ID: <33940.1542304792@turing-police.cc.vt.edu> (raw)
In-Reply-To: <tencent_37D7F80DFDD9120EFC281E281A758CA6F909@qq.com>
On Thu, 15 Nov 2018 23:53:56 +0800, "Larry" said:
> I'm curious when multiple process has the same PTE which points to the samepage,
> how can kernel differenciate which page from swap space should be swappedin?
The PTE tells where in /dev/swap to find the page. If it's a shared page, the
references all point at the same place, so "process 1's PAGE_A info" is the
same as "process 2's PAGE_A" info. They may have different addresses in the
two processes, but they're both referencing the same swap page.
> Process 2 get scheduled, PAGE_A was from Process 1, so it should be swapped out
Why? In general, there's no need to do so - and if it's shared, it's probably a hot page
so it won't be chosen for swapout.
(Remember - the kernel doesn't do swapin/swapout decisions in schedule(), it
only takes action once Process 2 starts running and references a page that requires
something be done.
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From: valdis.kletnieks@vt.edu
To: "Larry" <losemyheaven@foxmail.com>
Cc: kernelnewbies <kernelnewbies@kernelnewbies.org>
Subject: Re: a question on mapping from PTE to swap entry
Date: Thu, 15 Nov 2018 12:59:52 -0500 [thread overview]
Message-ID: <33940.1542304792@turing-police.cc.vt.edu> (raw)
Message-ID: <20181115175952.qUntF-Mh5sGBEILD86o59wrH9gjSozDcAReBYdRcTrY@z> (raw)
In-Reply-To: <tencent_37D7F80DFDD9120EFC281E281A758CA6F909@qq.com>
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On Thu, 15 Nov 2018 23:53:56 +0800, "Larry" said:
> I'm curious when multiple process has the same PTE which points to the samepage,
> how can kernel differenciate which page from swap space should be swappedin?
The PTE tells where in /dev/swap to find the page. If it's a shared page, the
references all point at the same place, so "process 1's PAGE_A info" is the
same as "process 2's PAGE_A" info. They may have different addresses in the
two processes, but they're both referencing the same swap page.
> Process 2 get scheduled, PAGE_A was from Process 1, so it should be swapped out
Why? In general, there's no need to do so - and if it's shared, it's probably a hot page
so it won't be chosen for swapout.
(Remember - the kernel doesn't do swapin/swapout decisions in schedule(), it
only takes action once Process 2 starts running and references a page that requires
something be done.
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next prev parent reply other threads:[~2018-11-15 17:59 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-15 15:53 a question on mapping from PTE to swap entry Larry
2018-11-15 15:53 ` Larry
2018-11-15 17:59 ` valdis.kletnieks at vt.edu [this message]
2018-11-15 17:59 ` valdis.kletnieks
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