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

[Jens Rehsack <rehsack@gmail.com>]

Am 04.08.2014 um 17:41 schrieb 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.

Today we received a BSP for our board for 3.10.17 - we might try it after first field test lunch (we want to see applications running - so this is just a side-theater :)
Important, but ... you know 8)

>> 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?

Precisely the same as in referred forum page - but IIRC a lot were posted earlier in the thread. I do not intend to spam list by reposting same information to often.
If you want, I prepare you a pastebin :)

>> 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.

But we need to be able to kick cached pages when we need it - I'm quite unsure whether (4) is a hack or an improvement - why only swapping is permitted to drop caches?

Cheers
-- 
Jens Rehsack
rehsack@gmail.com