Re: [RFC PATCH 2/2] rmap: remove parameter 'compound' from foeio_add_file_rmap_range()

["Yin, Fengwei" <fengwei.yin@intel.com>]

On 2/7/2023 12:50 AM, Matthew Wilcox wrote:
> On Mon, Feb 06, 2023 at 11:30:49PM +0800, Yin Fengwei wrote:
>> Remove parameter 'compound' from folio_add_file_rmap_range().
>>
>> The parameter nr_pages is checked whether same as folio page
>> numbers to know whether it's entire folio operation.
> 
> We can't do this yet.  Even if a folio is large enough to be PMD mapped,
> it may have been mapped askew (or its PMD mapping may have been split).
> We still need the caller to tell us whether it's been mapped with
> a PMD or with PTEs.
OK. My understand is that the info about PMD mapped is only for
statistic update. Maybe move the PMD mapped statistic to caller.

Another thing I am not sure whether it's worthy:
What about maintaining total mapcount for folio? So we don't need to
query each page mapcount to know it. So we can use "total_mapoucnt > 
mapped" to know whether the folio has at least one page mapped more
than once.

The payback is that we need update total mapcount when map/unmap
the folio.

Regards
Yin, Fengwei

>