Re: [PATCH v6 0/6] mm/vmalloc: Speed up ioremap, vmalloc and vmap with contiguous memory

[Dev Jain <dev.jain@arm.com>]

On 14/07/26 2:06 pm, Anshuman Khandual wrote:
> 
> 
> On 10/07/26 2:24 PM, Wen Jiang wrote:
>> On Fri, 10 Jul 2026 at 07:08, Andrew Morton <akpm@linux-foundation.org> wrote:
>>>
>>> On Thu,  9 Jul 2026 15:38:17 +0800 Wen Jiang <jiangwenxiaomi@gmail.com> wrote:
>>>
>>>> This patchset accelerates ioremap, vmalloc, and vmap when the memory
>>>> is physically fully or partially contiguous.
>>>
>>> Thanks, I added this to mm.git's mm-new branch for wider testing.
>>>
>>> AI review asked some questions, and some of them are new since the v5
>>> series:
>>>         https://sashiko.dev/#/patchset/20260709073823.6643-1-jiangwen6@xiaomi.com
>>
>> Hi Andrew,
>>
>> I've gone through the Sashiko findings:
>>
>> - Patch 1 (find_num_contig): Over-interpretation. No new hugetlbfs hstate
>>   is added. The extra sizes are only used by init_mm kernel mappings via.
> 
> But not sure if that is a right approach. If these multi CONT_PTE
> sized mappings need to be supported in vmalloc() but without adding
> corresponding HugeTLB sizes, probably these required helpers could
> just be factored outside HugeTLB.

The problem is that the existing vmalloc-huge code reuses the hugetlb helpers
because it is easier that way.

If you really look at it, num_contig_ptes(), set_huge_pte_at() and arch_make_huge_pte()
do not have anything to do with hugetlbfs, but with huge mappings. It is unfortunate
that these helpers are sitting in hugetlbpage.c . Really these functions should be
pulled out of CONFIG_HUGETLBFS and put into some common header - but I can't think
of a clean solution to this.

So I think for this series, the least we can do is add a comment to clarify that these
helpers can be used by non-hugetlbfs mm code to set multiple huge mappings at the PTE level.


>>
>> - Patch 5/6 (NULL page): Invalid input. vmap() expects a fully populated
>>     array of valid struct page pointers.
>>
>> - Patch 6 (32-bit count << PAGE_SHIFT overflow): Pre-existing. This was
>>     already discussed in the V3 thread, and a separate fix was proposed
>>     there.
>>
>> Thanks,
>> Wen
>