Claude review: mm: add rest_of_page() macro

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

Defines the macro and removes the original from net/9p:

```c
+#define rest_of_page(p)		(PAGE_SIZE - offset_in_page(p))
```

This is clean. The macro correctly relies on `offset_in_page()` for the cast to `unsigned long`, so it works with both pointers and integer types (loff_t, unsigned long, etc.). The return type is `unsigned long`, which is appropriate for a byte count within a page.

The removal of the `static unsigned int rest_of_page(void *data)` function from `net/9p/trans_virtio.c` is the exact equivalent. Note the original was `unsigned int` return and accepted `void *`, while the macro returns `unsigned long` — this is fine since the callers use the result in contexts that accept either width.

No issues.

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Generated by Claude Code Patch Reviewer