On Wed, Dec 3, 2014 at 7:15 PM, Chris Mason <c...@fb.com> wrote:
>
> One guess is that trinity is generating a huge number of tlb
> invalidations over sparse and horrible ranges. Perhaps the old code was
> falling back to full tlb flushes before Dave Hansen's string of fixes?
Hmm. I agree that we've had some of the backtraces look like TLB
flushing might be involved. Not all, though. And I'm not seeing where
a loop over up to 33 pages should matter over doing a full TLB flush.
What *might* matter is if we somehow get that number wrong, and the loops like
addr = f->flush_start;
while (addr < f->flush_end) {
__flush_tlb_single(addr);
addr += PAGE_SIZE;
}
ends up looping a *lot* due to some bug, and then the IPI itself would
take so long that the watchdog could trigger.
But I do not see how that could actually happen. As far as I can tell,
either the number of pages is limited to less than 33, or we have that
TLB_FLUSH_ALL case.
Do you see something I don't?
Linus
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