Re: [Crash-utility] Incorrect HighMem statistics
Dne Čt 12. ledna 2012 22:38:38 Petr Tesarik napsal(a):
Hi all,
it seems crash shows incorrect HighMem stats with recent kernels. E.g.:
crash> kmem -i
[...]
TOTAL HIGH 1821682 6.9 GB 93% of TOTAL MEM
FREE HIGH 0 0 0% of TOTAL HIGH
TOTAL LOW 132983 519.5 MB 6% of TOTAL MEM
FREE LOW 1333474 5.1 GB 1002% of TOTAL LOW
BTW note that total low is smaller than free low, which is obviously
incorrect. I believe that this is somehow related to the Movable zone,
because the code that counts free low pages checks for pages which belong
to ZONE_HIGHMEM, which is initialized as:
vt->ZONE_HIGHMEM = vt->nr_zones - 1;
My system has 4 zones:
ZONE NAME SIZE MEM_MAP START_PADDR START_MAPNR
0 DMA 4080 f4a02200 10000 0
1 Normal 221694 f4a22000 1000000 4080
2 HighMem 790002 f50e5fc0 371fe000 225774
3 Movable 0 0 0 0
And indeed, "help -v" shows:
[...]
dump_free_pages: dump_free_pages_zones_v2()
[...]
ZONE_HIGHMEM: 3
I don't know yet how to fix this, but maybe somebody can push me in the
right direction.
Maybe we should check the names in zone_names[]. AFAICS this array has existed
ever since the dawn of time, and the HIGHMEM_ZONE has always been called
"HighMem".
That already covers a lot of cases, but not the Movable zone, if it exists.
nr_free_highpages() contains:
if (zone_movable_is_highmem())
pages += zone_page_state(
&pgdat->node_zones[ZONE_MOVABLE],
NR_FREE_PAGES);
zone_movable_is_highmem() is defined as:
static inline int zone_movable_is_highmem(void)
{
#if defined(CONFIG_HIGHMEM) && defined(CONFIG_ARCH_POPULATES_NODE_MAP)
return movable_zone == ZONE_HIGHMEM;
#else
return 0;
#endif
}
Now, I think we don't have to take the preprocessor directives into account,
because movable_zone is automatically initialized to zero, and ZONE_HIGHMEM
can never be numerically equal to zero, so the test would be always false in
that case anyway.
We should only set vt->HIGHMEM_ZONE to something special (such as -1) if
CONFIG_HIGHMEM is not defined, and there is no highmem zone, because otherwise
we might hit a false positive for zone_movable_is_highmem.
Comments? Should I make the idea into a patch?
Petr Tesarik
SUSE Linux