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SubjectRe: [PATCH v2] page_alloc: Fix freeing non-compound pages
On Mon, Sep 28, 2020 at 06:03:07PM -0700, Andrew Morton wrote:
> Well that's weird and scary looking. `page' has non-zero refcount yet
> we go and free random followon pages. Methinks it merits an
> explanatory comment?

Here's some kernel-doc. Opinions?

/**
* __free_pages - Free pages allocated with alloc_pages().
* @page: The page pointer returned from alloc_pages().
* @order: The order of the allocation.
*
* This function differs from put_page() in that it can free multi-page
* allocations that were not allocated with %__GFP_COMP. This function
* does not check that the @order passed in matches that of the
* allocation, so it is possible to leak memory. Freeing more memory than
* was allocated will probably be warned about by other debugging checks.
*
* It is only safe to use the page reference count to determine when
* to free an allocation if you use %__GFP_COMP (in which case, you may
* as well use put_page() to free the page). Another thread may have a
* speculative reference to the first page, but it has no way of knowing
* about the rest of the allocation, so we have to free all but the
* first page here.
*
* Context: May be called in interrupt context but not NMI context.
*/

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