Date: Wed, 1 May 2002 10:28:15 -0700 (PDT) From: Lamont Granquist <lamont@scriptkiddie.org> To: David Schultz <dschultz@uclink.Berkeley.EDU> Cc: Rohit Grover <rohit@gojuryu.com>, <freebsd-hackers@FreeBSD.ORG> Subject: Re: VM Question (was Re: larger kernel virtual address space) Message-ID: <20020501102349.J6199-100000@coredump.scriptkiddie.org> In-Reply-To: <20020501002336.A14305@HAL9000.wox.org>
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On Wed, 1 May 2002, David Schultz wrote: > Thus spake Lamont Granquist <lamont@scriptkiddie.org>: > > Does the FreeBSD VM system do O(1) or O(N) searches for gaps in a > > processes virtual memory space? > > I'm not a VM guru, but if I'm reading vm_map.c right, it's O(n) > w.r.t. the number of map entries. But since map entries are merged > when possible, I would expect the cost to stay fairly low. I know of one app running on Linux/x86 which spends about 40% of its kernel time in get_unmapped_pages() (the Linux equivalent). Trying to mmap() bits and pieces of 20GB worth of data into a 4GB VM space tends to lead to a lot of fragmentation. Be interesting to see if merging would help, but I'd suggest an O(1) algorithm for this. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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