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SubjectRe: [ckrm-tech] RFC: Memory Controller
Pavel Emelianov wrote:
> Balbir Singh wrote:
>> Pavel Emelianov wrote:
>>> [snip]
>>>
>>>> Reclaimable memory
>>>>
>>>> (i) Anonymous pages - Anonymous pages are pages allocated by the user space,
>>>> they are mapped into the user page tables, but not backed by a file.
>>> I do not agree with such classification.
>>> When one maps file then kernel can remove page from address
>>> space as there is already space on disk for it. When one
>>> maps an anonymous page then kernel won't remove this page
>>> for sure as system may simply be configured to be swapless.
>> Yes, I agree if there is no swap space, then anonymous memory is pinned.
>> Assuming that we'll end up using a an abstraction on top of the
>> existing reclaim mechanism, the mechanism would know if a particular
>> type of memory is reclaimable or not.
>
> If memory is considered to be unreclaimable then actions should be
> taken at mmap() time, not later! Rejecting mmap() is the only way to
> limit user in unreclaimable memory consumption.

That's like disabling memory over-commit in the regular kernel.
Don't you think this should again be based on the systems configuration
of over-commit?

[snip]

>
>> I understand that kernel memory accounting is the first priority for
>> containers, but accounting kernel memory requires too many changes
>> to the VM core, hence I was hesitant to put it up as first priority.
>
> Among all the kernel-code-intrusive patches in BC patch set
> kmemsize hooks are the most "conservative" - only one place
> is heavily patched - this is slab allocator. Buddy is patched,
> but _significantly_ smaller. The rest of the patch adds __GFP_BC
> flags to some allocations and SLAB_BC to some kmem_caches.
>
> User memory controlling patch is much heavier...
>

Please see the patching of Rohit's memory controller for user
level patching. It seems much simpler.

> I'd set priorities of development that way:
>
> 1. core infrastructure (mainly headers)
> 2. interface
> 3. kernel memory hooks and accounting
> 4. mappings hooks and accounting
> 5. physical pages hooks and accounting
> 6. user pages reclamation
> 7. moving threads between beancounters
> 8. make beancounter persistent

I would prefer a different set

1 & 2, for now we could use any interface and then start developing the
controller. As we develop the new controller, we are likely to find the
need to add/enhance the interface, so freezing in on 1 & 2 might not be
a good idea.

I would put 4, 5 and 6 ahead of 3, based on the changes I see in Rohit's
memory controller.

Then take up the rest.

--

Balbir Singh,
Linux Technology Center,
IBM Software Labs
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