Date: Wed, 06 Jan 2010 16:27:09 -0800 From: Julian Elischer <julian@elischer.org> To: Pieter de Goeje <pieter@degoeje.nl> Cc: freebsd-hackers@freebsd.org, shrivatsan <shrivatsan@gmail.com> Subject: Re: Question regarding memory disks Message-ID: <4B452A5D.4000208@elischer.org> In-Reply-To: <201001070017.36855.pieter@degoeje.nl> References: <5a13b8941001061349m701d17fbl489ec8cf883e8c3c@mail.gmail.com> <201001070017.36855.pieter@degoeje.nl>
next in thread | previous in thread | raw e-mail | index | archive | help
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-unsubscribe@freebsd.org"
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?4B452A5D.4000208>