Thanks a lot for the response. --- On Wed, 1/6/10, Julian Elischer <jul...@elischer.org> wrote:
From: Julian Elischer <jul...@elischer.org> Subject: Re: Question regarding memory disks To: "Pieter de Goeje" <pie...@degoeje.nl> Cc: freebsd-hackers@freebsd.org, "shrivatsan" <shrivat...@gmail.com> Date: Wednesday, January 6, 2010, 7:27 PM Pieter de Goeje wrote: > On Wednesday 06 January 2010 22:49:44 shrivatsan wrote: >> Hi, >> >> I have configured a malloc-backed memory disk, and I mount the device on to >> the file system. I write some data onto the file system. I see that the >> free memory indicated by kmem_map_free goes down, and this is proportional >> to the size of the data written. However, even after removing all the >> data, kmem_map_free doesn't seem to go up. Its only after detaching the >> memory disk does the free memory go up. May I know the reason for this >> behavior? >> >> >> Thanks, >> -shrivatsan > > Because when you "erase" something, all it does is unlink (delete the > reference to) the data. So there is currently no way the memory disk can free > the memory associated with the data. That is also why you should normally use > swap backed memory disks instead, or use tmpfs. These can return memory to > the system. > > The ability of the filesystem to mark certain blocks as "erased" is important > not only for memory disks but also for solid state drives. It is a feature > UFS2 is currently lacking unfortunately. but is being worked on > > - Pieter > _______________________________________________ > freebsd-hackers@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-hackers > To unsubscribe, send any mail to "freebsd-hackers-unsubscr...@freebsd.org" _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "freebsd-hackers-unsubscr...@freebsd.org" _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "freebsd-hackers-unsubscr...@freebsd.org"
