Messages in this thread | | | Date | Wed, 02 Nov 2011 16:51:31 -0400 | From | Rik van Riel <> | Subject | Re: [GIT PULL] mm: frontswap (for 3.2 window) |
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On 10/31/2011 07:36 PM, Dan Magenheimer wrote: >> From: Andrea Arcangeli [mailto:aarcange@redhat.com]
>>> real work to do instead and (2) that vmexit/vmenter is horribly >> >> Sure the CPU has another 1000 VM to schedule. This is like saying >> virtio-blk isn't needed on desktop virt becauase the desktop isn't >> doing much I/O. Absurd argument, there are another 1000 desktops doing >> I/O at the same time of course. > > But this is truly different, I think at least for the most common > cases, because the guest is essentially out of physical memory if it > is swapping. And the vmexit/vmenter (I assume, I don't really > know KVM) gives the KVM scheduler the opportunity to schedule > another of those 1000 VMs if it wishes.
I believe the problem Andrea is trying to point out here is that the proposed API cannot handle a batch of pages to be pushed into frontswap/cleancache at one time.
Even if the current back-end implementations are synchronous and can only do one page at a time, I believe it would still be a good idea to have the API able to handle a vector with a bunch of pages all at once.
That way we can optimize the back-ends as required, at some later point in time.
If enough people start using tmem, such bottlenecks will show up at some point :)
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