Re: [Qemu-devel] QEMU_TMPDIR temp folder for KQEMU for Windows.

[Francois Rioux]

Filip,

 

I'm not trying to put the guest in ram.  As you state, let's Windows manage its whole memory, paging and swapping.  I agree it would be as dumb as setting up a ramdisk to put the swapfile. Let's not trying to outsmart the OS.

 

I was trying to follow Fabrice recommendation to set the QEMU temp directory to a RAM disk while using kqemu:

 

"When using KQEMU, QEMU will create a big hidden file containing the RAM of the virtual machine. For best performance, it is important that this file is kept in RAM and not on the hard disk. QEMU uses the `/dev/shm' directory to create this file because tmpfs is usually mounted on it (check with the shell command df). Otherwise `/tmp' is used as fallback. You can use the QEMU_TMPDIR shell variable to set a new directory for the QEMU RAM file. " (excerpt from his 'kqemu-doc.html' file).

I (maybe incorrectly) interpreted that as setting the temp dir in RAM.  But I'm not that familiar with Linux and I don't know what /shm or tmpfs are.  I guessed they were 'virtual' storage devices in RAM.  I'm simply trying to mimic that under Windows.  Had I been right, using a RAM disk to store the 'big hidden file containing the RAM of the virtual machine' would not be useless given enough ram is available, would it?  But I can't find that file at all under Windows and my understanding of the whole situation is probably wrong, or at least part of it.

 

Reading your other posts in this forum I understand you have an deep knowledge of Linux, Windows and QEMU insights so I take from your answer that RAMDISK is not gonna help kqemu.

 

Regards,

 

Francois

Filip Navara <address@hidden> wrote:

Francois Rioux wrote:
[snip]

> Ramdisk might have been a real performance accelerator for Windows
> hosts with enough RAM available. Since I can't find the temp memory
> image file is saved, I can't use that option.

Why do you think that it would improve performance? Sorry, but that's
complete rubbish... The guest RAM is allocated using standard virtual
memory functions and as long as you have enough memory the system will
probably leave it in the physical RAM anyway... If you don't, it's
swapped out to page file. This is much more versatile solution since you
don't have to reserve a chunk of the RAM for a disk and _permanently_
waste your memory resources this way...

>
>
> */"Jim C. Brown" /* wrote:

[snip]

> IIUC this is a reference to shmfs. So this doesn't apply to KQEMU
> on Windows
> hosts. I'm not an expert on the Windows versions tho, so I'm not
> 100% sure of
> this.
>
Correct.

- Filip


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