On Thu, Sep 25, 2014 at 2:55 PM, Peter Hurley peter@hurleysoftware.com wrote:
After several days uptime with a 3.16 kernel (generally running Thunderbird, emacs, kernel builds, several Chrome tabs on multiple desktop workspaces) I've been seeing some really extreme slowdowns.
Mostly the slowdowns are associated with gpu-related tasks, like opening new emacs windows, switching workspaces, laughing at internet gifs, etc. Because this x86_64 desktop is nouveau-based, I didn't pursue it right away -- 3.15 is the first time suspend has worked reliably.
This week I started looking into what the slowdown was and discovered it's happening during dma allocation through swiotlb (the cpus can do intel iommu but I don't use it because it's not the default for most users).
I'm still working on a bisection but each step takes 8+ hours to validate and even then I'm no longer sure I still have the 'bad' commit in the bisection. [edit: yup, I started over]
I just discovered a smattering of these in my logs and only on 3.16-rc+ kernels: Sep 25 07:57:59 thor kernel: [28786.001300] alloc_contig_range test_pages_isolated(2bf560, 2bf562) failed
This dual-Xeon box has 10GB and sysrq Show Memory isn't showing heavy fragmentation [1].
Besides Mel's page allocator changes in 3.16, another suspect commit is:
commit b13b1d2d8692b437203de7a404c6b809d2cc4d99 Author: Shaohua Li shli@kernel.org Date: Tue Apr 8 15:58:09 2014 +0800
x86/mm: In the PTE swapout page reclaim case clear the accessed bit instead of flushing the TLBSpecifically, this statement:
It could cause incorrect page aging and the (mistaken) reclaim of hot pages, but the chance of that should be relatively low.I'm wondering if this could cause worse-case behavior with TTM? I'm testing a revert of this on mainline 3.16-final now, with no results yet.
Thoughts?
You may also be seeing this: https://lkml.org/lkml/2014/8/8/445
Alex