Messages in this thread Patch in this message | | | Date | Mon, 22 May 2017 10:45:14 +0200 | From | Michal Hocko <> | Subject | Re: Widespread crashes in -next, bisected to 'mm: drop HASH_ADAPT' |
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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) -- Michal Hocko SUSE Labs
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