Subject: Re: X server as a Unix system process
To: Jukka Marin <firstname.lastname@example.org>
From: Jonathan Stone <jonathan@DSG.Stanford.EDU>
Date: 07/15/1997 01:27:44
Looks to me like the VM code is slowly growing a linked list
somewhere, when given repeated mmap()/munmap() calls for small
Jukka Marin writes:
>On Tue, Jul 15, 1997 at 10:35:32AM +0300, Jukka Marin wrote:
>> The three munmap() calls take over 20 ms! Why? It seems that these calls
>> are slowing down grtadually. During the last ktrace of the X server, they
>> were taking about 2 ms each.
>Getting even worse:
> 203 XF86_SVGA 0.000187 CALL mmap(0,0x27000,0x3,0x1002,0xffffffff,0,0,0)
> 203 XF86_SVGA 0.000143 RET mmap 286797824/0x11183000
> 203 XF86_SVGA 0.009413 CALL munmap(0x111aa000,0x27000)
> 203 XF86_SVGA 0.000227 RET munmap 0
> 203 XF86_SVGA 0.000057 CALL mmap(0,0x27000,0x3,0x1002,0xffffffff,0,0,0)
> 203 XF86_SVGA 0.000130 RET mmap 286957568/0x111aa000
> 203 XF86_SVGA 0.009094 CALL munmap(0x11117000,0x27000)
> 203 XF86_SVGA 0.000229 RET munmap 0
> 203 XF86_SVGA 0.000059 CALL mmap(0,0x27000,0x3,0x1002,0xffffffff,0,0,0)
> 203 XF86_SVGA 0.000132 RET mmap 286355456/0x11117000
> 203 XF86_SVGA 0.009397 CALL munmap(0x1113e000,0x27000)
> 203 XF86_SVGA 0.000224 RET munmap 0
>Almost 30 ms is spent in the munmap() calls now.
I havent' UTSLed or anything but this _really_ looks as if there's a
linked-list or other O(n) structure inside the kernel that's
accumulating overhead as time goes on.
Linux uses an AVL tree to keep track of the popuulated portions of a
process's address space. mmap()ing and un-mmap()ing lots of tiny
regions works okay there.
Your data suggests that on NetBSD, this runs into a performance bug.
It looks to me like you're gettin a different chunk of address space
each time, which is also consistent with a slowly-growing linked list.
(Where else would the state be kept?)