Re: [LI] Swap file system.

["Archan Paul" <archanp@xxxxxxxxxxx>]

Hi Subramania,

It is quite informative and interesting. Will provide some more details
regarding this?

Thanx is advance.

Archan Paul
archanp@xxxxxxxxxxx
http://www.bigfoot.com/~archanp


----- Original Message -----
From: T Subramania Sharma <sharmat@xxxxxxxxxxxxxxxxx>
To: <linux-india@xxxxxxxxxxxxxxxxxxxxx>
Sent: Sunday, October 17, 1999 10:40 AM
Subject: [LI] Swap file system.


> hi,
>
> this is regarding the swap filesystem. soory i didn't have a copy
> of the previous thread. The question is what file system the swap uses ?
>
> Swap in fact doesn't have any filesystem as such.
>
> The first 4kb (4096 bytes) of the swap space is used to maintain
> information about the swap.Of this the last 10 bytes have the
> signature "SWAP-SPACE" . The remaining 4086 bytes is used as a
> bitmap.The swap blocks are considered as 4k blocks.So if there
> is a 32 mb swap, the bits in the bitmap indicate where the
> corresponding blocks are there.This bitmap information is read
> from disk only once, when the system call swapon is called by the
> init process and the kernel set up corrresponding data structures
> which are used till the swap is removed by calling the system
> call 'swapoff'.
> The main parameters that are mainitained in the kernel data
> structure are a bitmap and an char array.Bits are set in the
> bitmap to indicate a read or write is taking place to a swap
> block corresponding to the bit set. The char array corresponding
> a swap block contains the count of many process have their pages
> swapped out to this block. When the count is zero, the
> correspodning swap block is free.
>
> - sharma
>
>
>
>
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