Messages in this thread | ![/](/images/icornerl.gif) | | Subject | Re: Widespread crashes in -next, bisected to 'mm: drop HASH_ADAPT' | From | Guenter Roeck <> | Date | Mon, 22 May 2017 02:03:21 -0700 |
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On 05/22/2017 01:45 AM, Michal Hocko wrote: > On Sat 20-05-17 09:26:34, Michal Hocko wrote: >> On Fri 19-05-17 09:46:23, Guenter Roeck wrote: >>> Hi, >>> >>> my qemu tests of next-20170519 show the following results: >>> total: 122 pass: 30 fail: 92 >>> >>> I won't bother listing all of the failures; they are available at >>> http://kerneltests.org/builders. I bisected one (openrisc, because >>> it gives me some console output before dying). It points to >>> 'mm: drop HASH_ADAPT' as the culprit. Bisect log is attached. >>> >>> A quick glance suggests that 64 bit kernels pass and 32 bit kernels fail. >>> 32-bit x86 images fail and should provide an easy test case. >> >> Hmm, this is quite unexpected as the patch is not supposed to change >> things much. It just removes the flag and perform the new hash scaling >> automatically for all requeusts which do not have any high limit. >> Some of those didn't have HASH_ADAPT before but that shouldn't change >> the picture much. The only thing that I can imagine is that what >> formerly failed for early memblock allocations is now suceeding and that >> depletes the early memory. Do you have any serial console from the boot? > > OK, I guess I know what it going on here. Adaptive has scaling is not > really suited for 32b. ADAPT_SCALE_BASE is just too large for the word > size and so we end up in the endless loop. So the issue has been > introduced by the original "mm: adaptive hash table scaling" but my > patch made it more visible because [di]cache has tables most probably > suceeded in the early initialization which didn't have HASH_ADAPT. > The following should fix the hang. I am not yet sure about the maximum > size for the scaling and something even smaller would make sense to me > because kernel address space is just too small for such a large has > tables. > --- > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index a26e19c3e1ff..70c5fc1fb89a 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -7174,11 +7174,15 @@ static unsigned long __init arch_reserved_kernel_pages(void) > /* > * Adaptive scale is meant to reduce sizes of hash tables on large memory > * machines. As memory size is increased the scale is also increased but at > - * slower pace. Starting from ADAPT_SCALE_BASE (64G), every time memory > - * quadruples the scale is increased by one, which means the size of hash table > - * only doubles, instead of quadrupling as well. > + * slower pace. Starting from ADAPT_SCALE_BASE (64G on 64b systems and 32M > + * on 32b), every time memory quadruples the scale is increased by one, which > + * means the size of hash table only doubles, instead of quadrupling as well. > */ > +#if __BITS_PER_LONG == 64 > #define ADAPT_SCALE_BASE (64ul << 30) > +#else > +#define ADAPT_SCALE_BASE (32ul << 20) > +#endif > #define ADAPT_SCALE_SHIFT 2 > #define ADAPT_SCALE_NPAGES (ADAPT_SCALE_BASE >> PAGE_SHIFT) > > I have seen another patch making it 64ull. Not sure if adaptive scaling on 32 bit systems really makes sense; unless there is a clear need I'd rather leave it alone.
Guenter
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