Date: Wed, 14 Sep 2011 09:57:46 -0400 From: Jonathan Vomacka <juvix88@gmail.com> To: Matthew Seaman <m.seaman@infracaninophile.co.uk> Cc: freebsd-questions@freebsd.org Subject: Re: Recommended SWAP space for large amounts of ram (8GB) Message-ID: <CABfwSFoNm_O1wdx2oKYWpUWBtOxKdWD8mozFt70yA--vz%2BJ0ew@mail.gmail.com> In-Reply-To: <4E70B269.4020900@infracaninophile.co.uk> References: <4E709F62.60705@gmail.com> <4E70B269.4020900@infracaninophile.co.uk>
next in thread | previous in thread | raw e-mail | index | archive | help
Excellent response. Thank you so much.
On Sep 14, 2011 9:56 AM, "Matthew Seaman" <m.seaman@infracaninophile.co.uk>
wrote:
>
> On 14/09/2011 13:34, Jonathan Vomacka wrote:
> > Each operating system seems to have different documentation regarding
> > what a decent swap size is for systems with large amounts of RAM. My
> > system only has 8GB of RAM. Some people have gone with the general idea
> > that 2X the amount of RAM is sufficient but for systems with large
> > amounts of memory 1X the amount of RAM is fine. I was also told that
> > anything over 2GB of SWAP space will cause performance issues on the
> > system and that it is not recommended.
> >
> > Either from the FreeBSD docs, or based on personal experiences, what is
> > the recommended swap space for a 8GB system? Your opinions are greatly
> > appreciated
>
> The old rule of thumb of swap = 2 x RAM dates back to the days when
> 128MB RAM was a big deal. Nowadays, you're likely to have that much in
> your phone, and systems with 128GB RAM are not unknown.
>
> In these days of plentiful RAM, the new rule of thumb is "if you're
> swapping, then you're doing it wrong." You don't need anything like as
> much swap nowadays, at least, not as compensation for lack of RAM. You
> may need swap to back eg. tmpfs filesystems. You don't need swap
> nowadays for system dumps -- any partition with ephemeral data (or no
> data at all) can be used for dumping, and given that minidump capability
> exists now, you don't even need to supply the 1 x RAM + delta required
> for a full dump.
>
> That swap > 2GB resulted in performance problems was certainly true
> once, but I doubt very much that it is still the case in HEAD or the
> upcoming 9.0-RELEASE, nor probably in {7,8}-STABLE. IIRC the problem
> was due to avoiding integer overflow in some calculations deep inside
> the VM system, which is usually not a hugely difficult problem to fix.
>
> My recommendation: for systems with 1GB RAM or more, and that don't make
> heavy use of memory filesystems and the like, then 2GB swap is ample,
> and you can probably get away with as little as 1GB at need.
>
> Cheers,
>
> Matthew
>
> --
> Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard
> Flat 3
> PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate
> JID: matthew@infracaninophile.co.uk Kent, CT11 9PW
>
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CABfwSFoNm_O1wdx2oKYWpUWBtOxKdWD8mozFt70yA--vz%2BJ0ew>