H. Peter Anvin wrote:
> Al Boldi wrote:
> > H. Peter Anvin wrote:
> >> Al Boldi wrote:
> >>> Isn't everything really just temporary?
> >>>
> >>> Would something like an mmap'd tmpfs be possible?
> >>
> >> No. tmpfs relies on being able to leave data structures in the running
> >> kernel. In particular, it has no metadata store at all.
> >>
> >> The needs for a persistent filesystem are very different, regardless of
> >> what the underlying medium is.
> >
> > Think Suspend-To-Disk; in that case tmpfs looks pretty persistent to me.
> >
> > So what does STD do? It pushes memory out to swap.
>
> It pushes ALL of (used) memory out to swap.
Ok.
> > Now, tmpfs could probably do the same thing on its own either to a
> > private swap or an mmap. I am suggesting mmap, as swap is currently
> > really slow with tmpfs, and switching it to use mmap may buy us 2 for
> > the price of 1.
>
> No.
>
> First of all, it would have to map ALL of kernel memory, or you would
> have to change the way things like dentries, inodes, and namespaces are
> allocated in the kernel itself.
That's probably one way of doing it.
> Second, you still would have no stability across kernel versions.
No problem. You could probably convince the user to do a tmpfs backup before
an upgrade.
> Third, you would have to accept total data loss on unclean shutdown,
> because tmpfs doesn't care about coherency, *NOR SHOULD IT*.
I think that's understood. But this risk could be reduced by instantiating
the latest sync'd mmap/swap.
> This is
> the fundamental reason why allocating a large swap partition and making
> /tmp a tmpfs can give a *huge* performance boost, even though it still
> hits disk.
Don't know what you mean here. Do you mean that tmpfs performance is
dependent on free swap-space being larger than some threshold. If so, what
threshold causes a tmpfs slowdown?
> What you're talking about is, *and should be*, a different filesystem.
> You will relatively quickly find that you have to deal with the same
> kind of stuff that you have to in any filesystem.
That's exactly what I want to avoid, as this would introduce a performance
penalty.
All we need is a periodically synced tmpfs to mmap, with a minimal stream
into page-cache algo on mount.
Thanks!
--
Al
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
