Re: rust_binder: use KVVec for files_to_translate

[SCADA StrangeLove]

Thanks for the review!

> One it looks like you're missing [PATCH] in the email title.
> Also, as checkpatch points out, Suggested-by must be an email
> address.

Both fixed in v2 (sending shortly).

> Also, should the close_on_free vector also be a KVVec?

No -- close_on_free is 4 bytes/entry, matching the wire format, so its
worst case is ~1,048,554 entries (~4 MiB, exactly SZ_4M - 88 bytes).
That fits under KMALLOC_MAX_SIZE on every config rust_binder ships on
today, but only because SZ_4M and KMALLOC_MAX_SIZE happen to coincide,
not because anything enforces it -- if either constant changes, this
stops being true. files_to_translate and reservations don't have that
margin at all: they blow past 4 MiB at far lower fd counts because
their per-entry kernel size is larger than the wire size, which is why
those two need the fix regardless.

Sergey

чт, 27 авг. 2026 г. в 10:07, Alice Ryhl <aliceryhl@xxxxxxxxxx>:
>
> On Tue, Aug 25, 2026 at 07:17:12PM +0300, scadastrangelove wrote:
> > From: Sergey Gordeychik <scadastrangelove@xxxxxxxxx>
> >
> > The num_fds value in a binder_fd_array_object is bounded by the
> > transaction buffer. However, its in-kernel metadata is larger than the
> > u32 array on the wire.
> >
> > On 64-bit systems, FileEntry occupies 24 bytes. About 900,000 entries
> > therefore make files_to_translate request roughly 20.6 MiB of
> > physically contiguous memory, triggering a warning in
> > __alloc_frozen_pages_noprof.
> >
> > translate_fds() later allocates Reservation entries from the same
> > count. At 16 bytes per entry, this requires another 13.7 MiB contiguous
> > allocation.
> >
> > Neither vector requires physical contiguity. Use KVVec for both so
> > large allocations can fall back to vmalloc.
> >
> > Keep close_on_free as KVec because its u32 storage matches the wire
> > representation and does not reach the allocation sizes above.
> >
> > Tested under QEMU/KVM. The 900,000-entry reproducer no longer triggers
> > a page allocator warning, and a 300,000-entry transaction that repeats
> > one valid fd reaches translate_fds() without WARN or BUG.
> >
> > Suggested-by: rust-in-peace agentic pipeline
> > Signed-off-by: Sergey Gordeychik <scadastrangelove@xxxxxxxxx>
>
> A few things. One it looks like you're missing [PATCH] in the email
> title. Also, as checkpatch points out, Suggested-by must be an email
> address.
>
> Also, should the close_on_free vector also be a KVVec?
>
> Otherwise this looks good to me.
>
> Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
>
> Alice