> On Sep 21, 2026, at 11:43, Qi Zheng <[email protected]> wrote:
> On 9/19/26 10:07 PM, Muchun Song wrote:
>>> On Sep 19, 2026, at 22:01, Qi Zheng <[email protected]> wrote:
>>> On 9/13/26 4:37 PM, Muchun Song wrote:
>>>> VMEMMAP_POPULATE_DAX currently distinguishes DAX vmemmap population in two
>>>> places: it keeps allocations on the normal path and takes a reference when
>>>> a backing page is supplied for reuse.
>>>> After Device DAX switched to the common per-zone shared tail page, both
>>>> conditions can be determined locally. DAX supplies ptpfn for every shared
>>>> tail mapping and requests an allocation only for compound head mappings,
>>>> whose PFNs are not optimizable. Therefore, vmemmap_optimizable_pfn() alone
>>>> selects the correct allocation path.
>>>> When ptpfn is supplied, the caller is reusing an existing backing page.
>>>> Once the slab allocator is available, take a reference for each reused
>>>
>>> Does the availability of slab mean the buddy allocator is already being
>>> used? Could there be a window where the buddy allocator is functional
>>> but slab hasn't become available yet?
>> Yes, because the slab allocator is based on buddy allocator. But I want to
>> know
>> what's your concern here?
>
> The goal here is to check if the buddy allocator is ready, but the code
> actually checks for slab.
>
> I'm concerned there could be a gap between these two:
>
> buddy is ready <-- gap --> slab is ready
There is no vmemmap population during the gap. We don't need to concern the gap.
Thanks.
>
> Thanks,
> Qi
>
>
