Messages in this thread | | | Subject | Re: [PATCH v3 27/34] mm: pagewalk: Add 'depth' parameter to pte_hole | From | Dave Hansen <> | Date | Thu, 28 Feb 2019 11:00:17 -0800 |
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On 2/28/19 3:28 AM, Steven Price wrote: > static int get_level(unsigned long addr, unsigned long end) > { > /* Add 1 to account for ~0ULL */ > unsigned long size = (end - addr) + 1; > if (size < PMD_SIZE) > return 4; > else if (size < PUD_SIZE) > return 3; > else if (size < P4D_SIZE) > return 2; > else if (size < PGD_SIZE) > return 1; > return 0; > } > > There are two immediate problems with that: > > * The "+1" to deal with ~0ULL is fragile > > * PGD_SIZE isn't what you might expect, it's not defined for most > architectures and arm64/x86 use it as the size of the PGD table. > Although that's easy enough to fix up. > > Do you think a function like above would be preferable?
The question still stands of why we *need* the depth/level in the first place. As I said, we obviously need it for printing out the "name" of the level. Is that it?
> The other option would of course be to just drop the information from > the debugfs file about at which level the holes are. But it can be > useful information to see whether there are empty levels in the page > table structure. Although this is an area where x86 and arm64 differ > currently (x86 explicitly shows the gaps, arm64 doesn't), so if x86 > doesn't mind losing that functionality that would certainly simplify things!
I think I'd actually be OK with the holes just not showing up. I actually find it kinda hard to read sometimes with the holes in there. I'd be curious what others think though.
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