Re: [PATCH v4 4/7] x86/tlb: fall back to flush all when meet a THP large page

[Andrea Arcangeli <aarcange@redhat.com>]

Hi,

On Thu, May 10, 2012 at 01:00:10PM +0800, Alex Shi wrote:
> +	for (addr = start; addr <= end; addr += HPAGE_SIZE) {
> +		pgd = pgd_offset(mm, addr);
> +		if (likely(!pgd_none(*pgd))) {
> +			pud = pud_offset(pgd, addr);
> +			if (likely(!pud_none(*pud))) {
> +				pmd = pmd_offset(pud, addr);
> +				if (likely(!pmd_none(*pmd)))
> +					if (pmd_large(*pmd))
> +						return 1;

Note with THP we've to set the pmd temporarily not present during
split_huge_page just before it returns a regular pmd (to avoid erratas
and mixing 4k and 2m tlb on the same physical page). So pmd_large
would fail in that small time window and we would do the invlpg loop
(which should still work safe so no big deal). But I believe you could
use pmd_trans_huge above, maybe gcc can drop the whole block with
CONFIG_TRANSPARENT_HUGEPAGE=n.