Re: Right lib-imx/firmware-imx ... versions

[John Weber <rjohnweber@gmail.com>]

Hi Jens-

On 8/2/14, 9:59 AM, Jens Rehsack wrote:
> Daiane, because you also was involved into https://community.freescale.com/thread/304414:
>
> I digged a lot deeper, tried https://github.com/wandboard-org/linux/commit/7cbd06b2904c1855109084ca6b0c84990bc69233
> and debugged and proved more there ...
Have you forward-ported this to 3.10.17?  If so, it seems that the only downside 
for this is that it preallocates a lot of memory for the VPU.  It really 
shouldn't be necessary as long as page caching works properly, as I understand it.

> I also tried to get a picture of vmm by browsing "Understanding The Linux Virtual Memory Manager" by Mel Gorman.
>
> My result: When no swap is configured (and the box has none - because of 1GB RAM and 4GB Flash there is not really space for swap), the memory runs full by page-caching disk files.
Are you seeing some error messages here that you can post?
>
> There could be several ways out to ensure system is not crashing when pages for DMA are allocated by eg. XBMC, gplay or whatever wants to use the VPU.
>
> 1) continuously drop page cache (our measurement tells in our configuration every 15sec is fine even for 4K movies)
> 2) implement better dma page cache as v4l2 patch demonstrates (pre-alloc 256M and serve dma pages from there, use smart allocation as SmartHeap does and https://github.com/wandboard-org/linux/commit/7cbd06b2904c1855109084ca6b0c84990bc69233 drafts ...)
> 3) modify vpu dma allocator to interfere with page cache and drop oldest cache entries
> 4) find a way to simulate swap-conditions without really paging out
This (4) seems like a hack.  We need to be able to turn off swap without having 
to simulate it.
>
> Any hints choosing the optimal decision will be appreciated :)
>
> Best regards