Re: [RFC PATCH 00/16] mm/madvise: batch tlb flushes for MADV_DONTNEED and MADV_FREE

[Matthew Wilcox]

On Wed, Mar 05, 2025 at 10:15:55AM -0800, SeongJae Park wrote:
> For MADV_DONTNEED[_LOCKED] or MADV_FREE madvise requests, tlb flushes
> can happen for each vma of the given address ranges.  Because such tlb
> flushes are for address ranges of same process, doing those in a batch
> is more efficient while still being safe.  Modify madvise() and
> process_madvise() entry level code path to do such batched tlb flushes,
> while the internal unmap logics do only gathering of the tlb entries to
> flush.

Do real applications actually do madvise requests that span multiple
VMAs?  It just seems weird to me.  Like, each vma comes from a separate
call to mmap [1], so why would it make sense for an application to
call madvise() across a VMA boundary?

[1] Yes, I know we sometimes merge and/or split VMAs