----- Original Message -----
> 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".
I agree -- I'm sure my original intent was based upon paranoia that it
might change.
> 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.
Maybe you could first determine whether the kernel symbol "movable_zone" exists,
and if so, what it contains:
...
int movable_zone;
EXPORT_SYMBOL(movable_zone);
#endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
>
> 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?
Absolutely -- I'm waiting... ;-)
Thanks,
Dave
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