Re: [PATCH v3 01/12] mm/debug_vm_pgtable: Introduce struct pgtable_debug_args

[Gavin Shan]

Hi Anshuman,

On 7/22/21 5:08 PM, Anshuman Khandual wrote:
> On 7/22/21 11:53 AM, Gavin Shan wrote:
> > On 7/22/21 2:41 PM, Anshuman Khandual wrote:
> > > On 7/21/21 3:50 PM, Gavin Shan wrote:
> > > > On 7/21/21 3:44 PM, Anshuman Khandual wrote:
> > > > > On 7/19/21 6:36 PM, Gavin Shan wrote:
> > > > > > In debug_vm_pgtable(), there are many local variables introduced to
> > > > > > track the needed information and they are passed to the functions for
> > > > > > various test cases. It'd better to introduce a struct as place holder
> > > > > > for these information. With it, what the functions for various test
> > > > > > cases need is the struct, to simplify the code. It also makes code
> > > > > > easier to be maintained.
> > > > > >
> > > > > > Besides, set_xxx_at() could access the data on the corresponding pages
> > > > > > in the page table modifying tests. So the accessed pages in the tests
> > > > > > should have been allocated from buddy. Otherwise, we're accessing pages
> > > > > > that aren't owned by us. This causes issues like page flag corruption.
> > > > > >
> > > > > > This introduces "struct pgtable_debug_args". The struct is initialized
> > > > > > and destroyed, but the information in the struct isn't used yet. They
> > > > > > will be used in subsequent patches.
> > > > > >
> > > > > > Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
> > > > > > ---
> > > > > >     mm/debug_vm_pgtable.c | 197 +++++++++++++++++++++++++++++++++++++++++-
> > > > > >     1 file changed, 196 insertions(+), 1 deletion(-)

[...]

> > > IIRC it is also not guaranteed that PMD_SHIFT <= (MAX_ORDER - 1). Hence
> > > this same scheme should be followed for PMD level allocation as well.
> >
> > In theory, it's possible to have PMD_SHIFT <= (MAX_ORDER - 1) with misconfigured
> > kernel. I will apply the similar logic to PMD huge page in v4.
> >
> > > >       [... The code to release the PUD huge page needs changes based on @args->is_contiguous_pud_page]
> > >
> > > Right, a flag would be needed to call the appropriate free function.
> >
> > Yes. We need two falgs for PUD and PMD huge pages separately.
>
> A single flag should be enough, the order would be dependent on
> whether args->pud_pfn or args->pmd_pfn is valid.

Yes, it's correct that one flag is enough as we're sharing the PUD
or PMD huge page.

Thanks,
Gavin