On Mon, 20 Jul 2026 15:38:26 +0100 "Lorenzo Stoakes (ARM)" <[email protected]>
wrote:
> In memory management we've managed to manufacture a great deal of confusion
> around the concept of anonymous memory. We have:
>
> 1. 'Pure anon' memory - anonymous VMAs whose folios are anonymous and
> swap-backed (thus for reclaim purposes, treated as anonymous). These are
> simple enough.
>
> 2. shmem - file-backed VMAs, file-backed folios (from rmap perspective) so
> present in the page cache and mapped by an address_space object, but
> whose folios are also swap-backed (thus treated as anonymous for reclaim
> purposes).
>
> 3. MAP_PRIVATE-mapped /dev/zero - a strange beast whose VMAs have
> vma->vm_file set, but whose mmap_prepare callback clears vma->vm_ops to
> satisfy vma_is_anonymous(), which results in VMAs that were mmap()'d
> referencing a file, but are in every other sense anonymous, including the
> folios.
>
> 4. Other MAP_PRIVATE-file backed mappings - These possess file-backed VMAs
> and have file-backed folios until CoW'd, at which point those CoW'd
> folios are anonymous.
>
> This series fixes issues 3 and 4.
Thanks, I'll add this to mm-new for review-n-test.
AI review seems overloaded at present, might have found a few things:
https://sashiko.dev/#/patchset/[email protected]
