Re: [PATCH v2] mm: fault in complete folios instead of individual pages for tmpfs

[Vishal Moola (Oracle)]

On Fri, Jul 04, 2025 at 11:19:26AM +0800, Baolin Wang wrote:
> After commit acd7ccb284b8 ("mm: shmem: add large folio support for tmpfs"),
> tmpfs can also support large folio allocation (not just PMD-sized large
> folios).
> 
> However, when accessing tmpfs via mmap(), although tmpfs supports large folios,
> we still establish mappings at the base page granularity, which is unreasonable.
> 
> We can map multiple consecutive pages of a tmpfs folios at once according to
> the size of the large folio. On one hand, this can reduce the overhead of page
> faults; on the other hand, it can leverage hardware architecture optimizations
> to reduce TLB misses, such as contiguous PTEs on the ARM architecture.
> 
> Moreover, tmpfs mount will use the 'huge=' option to control large folio
> allocation explicitly. So it can be understood that the process's RSS statistics
> might increase, and I think this will not cause any obvious effects for users.
> 
> Performance test:
> I created a 1G tmpfs file, populated with 64K large folios, and write-accessed it
> sequentially via mmap(). I observed a significant performance improvement:
> 
> Before the patch:
> real	0m0.158s
> user	0m0.008s
> sys	0m0.150s
> 
> After the patch:
> real	0m0.021s
> user	0m0.004s
> sys	0m0.017s
> 
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>

Reviewed-by: Vishal Moola (Oracle) <vishal.moola@xxxxxxxxx>