Re: [PATCH v2] hugetlb: don't delete vma_lock in hugetlb MADV_DONTNEED processing

[Nadav Amit]

On Oct 29, 2022, at 5:15 PM, Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:

> zap_page_range is a bit confusing.  It appears that the passed range can
> span multiple vmas.  Otherwise, there would be no do while loop.  Yet, there
> is only one mmu_notifier_range_init call specifying the passed vma.
> 
> It appears all callers pass a range entirely within a single vma.
> 
> The modifications above would work for a range within a single vma.  However,
> things would be more complicated if the range can indeed span multiple vmas.
> For multiple vmas, we would need to check the first and last vmas for
> pmd sharing.
> 
> Anyone know more about this seeming confusing behavior?  Perhaps, range
> spanning multiple vmas was left over earlier code?

I don’t have personal knowledge, but I noticed that it does not make much
sense, at least for MADV_DONTNEED. I tried to batch the TLB flushes across
VMAs for madvise’s. [1]

Need to get to it sometime.

[1] https://lore.kernel.org/lkml/20210926161259.238054-7-namit@xxxxxxxxxx/