Re: dynamic_pager and context switching
Re: dynamic_pager and context switching
- Subject: Re: dynamic_pager and context switching
- From: Jim Magee <email@hidden>
- Date: Mon, 9 Feb 2004 16:42:12 -0500
Actually, the daemon is involved in compacting swap.
We add and subtract swap files based on total available free space in
the swap files. When we decide to remove a swap file, there may still
be contents in it. If there are, the dynamic_pager daemon's thread is
the one used to bring those contents back into memory and out to its
new home on another swap file. But it never leaves the kernel while
doing this (but it is unavailable to respond to additional swap file
need/excess notifications while doing it).
--Jim
On Feb 9, 2004, at 12:53 PM, Mike Smith wrote:
dynamic_pager just creates/deletes the swapfiles. It's not involved
in the I/O path, nor does it actually compact swap.
= Mike
On Feb 8, 2004, at 3:44 PM, Brian Tabone wrote:
I was digging through the darwin kernel lists, and did some cursory
searches on developer.apple.com, but I didn't find the answer. My
question is , does the kernel turn to dynamic_pager every time it
swaps pages in and out, or does dynamic_pager simply manage the swap
file(s) and grow/shrink them based on usage by the kernel? The reason
I ask is that it would seem a large performance penalty to have to
context switch out to a user-space daemon for every page in/out
request. Not only would you be contesting with page swaps, but you
would further be slowed down by expensive context switching from
kernel to user space.
Thanks in advance,
-Brian T
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