Re: [RFC PATCH v2 1/7] mm: pgtable: make pte_offset_map_nolock() return pmdval

[Qi Zheng <zhengqi.arch@bytedance.com>]

Hi David,

On 2024/8/5 22:43, David Hildenbrand wrote:
> On 05.08.24 14:55, Qi Zheng wrote:
>> Make pte_offset_map_nolock() return pmdval so that we can recheck the
>> *pmd once the lock is taken. This is a preparation for freeing empty
>> PTE pages, no functional changes are expected.
> 
> Skimming the patches, only patch #4 updates one of the callsites 
> (collapse_pte_mapped_thp).

In addition, retract_page_tables() and reclaim_pgtables_pmd_entry()
also used the pmdval returned by pte_offset_map_nolock().

> 
> Wouldn't we have to recheck if the PMD val changed in more cases after 
> taking the PTL?
> 
> If not, would it make sense to have a separate function that returns the 
> pmdval and we won't have to update each and every callsite?

pte_offset_map_nolock() had already obtained the pmdval previously, just
hadn't returned it. And updating those callsite is simple, so I think
there may not be a need to add a separate function.

Thanks,
Qi

>