Re: [PATCH v3 0/6] mm/vmalloc: Speed up ioremap, vmalloc and vmap with contiguous memory

[Wen Jiang]

On Sat, 23 May 2026 at 02:07, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Fri, 22 May 2026 13:31:40 +0800 Wen Jiang <jiangwenxiaomi@xxxxxxxxx> wrote:
>
> > This patchset accelerates ioremap, vmalloc, and vmap when the memory
> > is physically fully or partially contiguous.
>
> Thanks.  AI review asked a few things and might have found an existing
> 32-bit bug in vmap():
>
>         https://sashiko.dev/#/patchset/20260522053146.83209-1-jiangwenxiaomi@xxxxxxxxx

Hi Andrew,

I've gone through the Sashiko findings:

- Patch 5 (arch_vmap_pte_supported_shift on x86): Over-interpretation.
  This targets ARM64 CONT_PTE. x86 falls through with PAGE_SHIFT
  same as before.

- Patch 5 (1 << order overflow at order=31): Over-interpretation.
  Reaching order=31 requires 8TB contiguous in a single vmap()
  not a realistic usage pattern.

- Patch 6 (GFP_KERNEL triggering purge): The purge only triggers
  when vmalloc space is already under pressure, and benefits the
  subsequent PAGE_SIZE fallback as well, not wasted work.

- Patch 6 (32-bit count << PAGE_SHIFT overflow): Pre-existing.
  Will send a separate fix.

- Patch 6 (unconditional alignment without checking contiguity):
  The main vmap() users typically pass contiguous pages
  (e.g. system_heap order 8 -> 4 -> 0).

Thanks,
Wen