[gentoo-user] Re: aligning SSD partitions

[Nicolas Sebrecht <nsebrecht@piing.fr>]

The 06/09/12, Dale wrote:

> But whether it is on tmpfs or just regular memory doesn't matter.  Once
> emerge starts, everything is in ram including portages work directory
> which would be on tmpfs here.  That's why it doesn't matter if portage
> is on tmpfs or not.  Once emerge loads up the files, it's the same
> thing.  That's why using tmpfs doesn't matter.  I knew that the whole
> time.  The amount of ram on a system doesn't matter either.  If you have
> a system that doesn't have a lot of ram, then you can't really use tmpfs
> anyway.  That is not something I would recommend to anyone. 

But you're wrong with this assumption. I guess you never tried to
upgrade a Gentoo system running as server (a working one, with users and
workload).

The amount of memory is only /one/ helper parameter to not see a
difference.

Like I've already said, the issue is all about the persistence strategy
used by the VM to mark memory as pinned, reclaimable or swappable. Where
tmpfs do change the matter is that a file stored in it is not going be
dropped from RAM until there is a unlink(2) call on it or that other
running processes are running out of memory and some page needs to be
swapped (so there is _already_ no more available RAM in the kernel cache).

If not using tmpfs and because memory cache is the first place where the
kernel will free up memory, you don't have to wait for the processes to
run out of available memory to hit a situation where you'll have to wait
for the disk to retrieve files. So, this will affect times.

-- 
Nicolas Sebrecht