[PATCH 05/13] drm/ttm: overhaul memory accounting
j.glisse at gmail.com
Thu Nov 10 15:33:56 PST 2011
On Thu, Nov 10, 2011 at 09:05:22PM +0100, Thomas Hellstrom wrote:
> On 11/10/2011 07:05 PM, Jerome Glisse wrote:
> >On Thu, Nov 10, 2011 at 11:27:33AM +0100, Thomas Hellstrom wrote:
> >>On 11/09/2011 09:22 PM, j.glisse at gmail.com wrote:
> >>>From: Jerome Glisse<jglisse at redhat.com>
> >>>This is an overhaul of the ttm memory accounting. This tries to keep
> >>>the same global behavior while removing the whole zone concept. It
> >>>keeps a distrinction for dma32 so that we make sure that ttm don't
> >>>starve the dma32 zone.
> >>>There is 3 threshold for memory allocation :
> >>>- max_mem is the maximum memory the whole ttm infrastructure is
> >>> going to allow allocation for (exception of system process see
> >>> below)
> >>>- emer_mem is the maximum memory allowed for system process, this
> >>> limit is> to max_mem
> >>>- swap_limit is the threshold at which point ttm will start to
> >>> try to swap object because ttm is getting close the max_mem
> >>> limit
> >>>- swap_dma32_limit is the threshold at which point ttm will start
> >>> swap object to try to reduce the pressure on the dma32 zone. Note
> >>> that we don't specificly target object to swap to it might very
> >>> well free more memory from highmem rather than from dma32
> >>>Accounting is done through used_mem& used_dma32_mem, which sum give
> >>>the total amount of memory actually accounted by ttm.
> >>>Idea is that allocation will fail if (used_mem + used_dma32_mem)>
> >>>max_mem and if swapping fail to make enough room.
> >>>The used_dma32_mem can be updated as a later stage, allowing to
> >>>perform accounting test before allocating a whole batch of pages.
> >>Jerome, you're removing a fair amount of functionality here, without
> >>why it could be removed.
> >All this code was overkill.
>  I don't agree, and since it's well tested, thought throught and
> working, I see no obvious reason to alter it,
> within the context of this patch series unless it's absolutely
> required for the functionality.
Well one thing i can tell is that it doesn't work on radeon, i pushed
a test to libdrm and here it's the oom that starts doing its beating.
Anyway i won't alter it. Was just trying to make it works, ie be useful
while also being simpler.
> >>Consider a low-end system with 1G of kernel memory and 10G of
> >>highmem. How do we avoid putting stress on the kernel memory? I also
> >>wouldn't be too surprised if DMA32 zones appear in HIGHMEM systems
> >>in the future making the current zone concept good to keep.
> >Right now kernel memory is accounted against all zone so it decrease
> >not only the kernel zone but also the dma32& highmem if present.
> Do you mean that the code is incorrect? In that case, did you
> consider the fact
> that zones may overlap? (Although I admit the name "highmem" might
> be misleading. Should be "total").
Yeah i am well aware that zone overlap :)
> >Note also that kernel zone in current code == dma32 zone.
> Last time I looked, the highmem split was typically at slightly less
> than 1GB, depending on the hardware and desired setup. I admit that
> was some time ago, but has that really changed? On all archs?
> Furthermore, on !Highmem systems, All pages are in the kernel zone.
I was bit too much focused on my system where 1G of ram is wonderland
and 512M is the average. Thx to AMD i got a system with 8G i should
use it more.
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