linux-kernel - Re: Raid 0 Swap?

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Message-ID: <Pine.LNX.4.61.0609041242350.17115@yvahk01.tjqt.qr>
Date:	Mon, 4 Sep 2006 12:46:31 +0200 (MEST)
From:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
To:	Michael Tokarev <mjt@....msk.ru>
cc:	Helge Hafting <helge.hafting@...el.hist.no>,
	Marc Perkel <marc@...kel.com>, linux-kernel@...r.kernel.org
Subject: Re: Raid 0 Swap?

>> I thought kernel data weren't swapped at all?

If the swap code was swapped, who would swap it in again?

>Well, it's not that simple.  Kernel uses both swappable and
>non-swappable memory internally.  For some things, it's
>unswappable, for some, it's swappable.  In general, it's
>impossible to say which parts of kernel will break (and
>in wich ways) if swap goes havoc.

In general, everything you type in as C code (.bss, .data, .text) should be 
unswappable. kmalloc()ed areas are resident too, and kmalloc has a 
parameter which defines whether the allocation can/cannot push userspace 
pages into the swap (GFP_ATOMIC/GFP_IO). So if there is some 
kernel-allocation swapped out, it is most likely to be marked as 
'userspace' so that the same algorithms can be used for swapin and -out.

Jan Engelhardt
-- 

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VGER BF report: H 5.48632e-07
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