On 8/15/24 1:13 AM, Matthew Wilcox wrote:

On Tue, Jul 30, 2024 at 02:46:54PM +0800, alexs@kernel.org wrote:

quoted

We have struct ptdesc for page table descriptor a year ago, but it
has no much usages in kernel, while pgtable_t is used widely.

Hum, I thought I responded to this to point out the problem, but
I don't see the response anywhere, so I'll try again.

quoted

The pgtable_t is typedefed as 'pte_t *' in sparc, s390, powerpc and m68k
except SUN3, others archs are all same as 'struct page *'.

And there's a very good reason for that.  On s390 and powerpc (I cannot
speak to the sparc/m68k), each page table is (potentially) smaller
than PAGE_SIZE.  So we cannot do what your patch purports to do, as
we would not know whether we're referring to the first or subsequent
page tables contained within a page.

quoted

Maybe at some point in the distant future we'll be able to allocate

a ptdesc per page table instead of per page allocated for use by page
tables.  But we cannot do that yet.

Got it. Thanks a lot for the info!