On Tue 26-03-19 13:39:14, Anshuman Khandual wrote:
> Hello,
>
> early_memtest() is being executed on many platforms even though they dont enable
> CONFIG_MEMTEST by default. Just being curious how the following set of patterns
> got decided. Are they just random 64 bit patterns ? Or there is some particular
> significance to them in detecting bad memory.
>
> static u64 patterns[] __initdata = {
> /* The first entry has to be 0 to leave memtest with zeroed memory */
> 0,
> 0xffffffffffffffffULL,
> 0x5555555555555555ULL,
> 0xaaaaaaaaaaaaaaaaULL,
> 0x1111111111111111ULL,
> 0x2222222222222222ULL,
> 0x4444444444444444ULL,
> 0x8888888888888888ULL,
> 0x3333333333333333ULL,
> 0x6666666666666666ULL,
> 0x9999999999999999ULL,
> 0xccccccccccccccccULL,
> 0x7777777777777777ULL,
> 0xbbbbbbbbbbbbbbbbULL,
> 0xddddddddddddddddULL,
> 0xeeeeeeeeeeeeeeeeULL,
This are setting different bit patterns, a single/two/three bit(s) at a
different possition of the work.
> 0x7a6c7258554e494cULL, /* yeah ;-) */
Looks like an easter egg string to me.
--
Michal Hocko
SUSE Labs
