On 4/5/22 12:29, David Hildenbrand wrote:
>> +
>> +/*
>> + * This function checks whether a page is free && is the buddy
>> + * we can coalesce a page and its buddy if
>> + * (a) the buddy is not in a hole (check before calling!) &&
>> + * (b) the buddy is in the buddy system &&
>> + * (c) a page and its buddy have the same order &&
>> + * (d) a page and its buddy are in the same zone.
>> + *
>> + * For recording whether a page is in the buddy system, we set PageBuddy.
>> + * Setting, clearing, and testing PageBuddy is serialized by zone->lock.
>> + *
>> + * For recording page's order, we use page_private(page).
>> + */
>> +static inline bool page_is_buddy(struct page *page, struct page *buddy,
>> + unsigned int order)
>
> Nit: Strange indentation of the last parameter. But it's already in the
> code you're moving, so ...
>
>> +{
>> + if (!page_is_guard(buddy) && !PageBuddy(buddy))
>> + return false;
>> +
>> + if (buddy_order(buddy) != order)
>> + return false;
>> +
>> + /*
>> + * zone check is done late to avoid uselessly calculating
>> + * zone/node ids for pages that could never merge.
>
> I know, this is from existing code. But there really isn't a node check
> when relying on the zone id. I hope we are not missing a node check :)
AFAIK "zone_id" is in fact the combination of node+zone (or section+zone),
so it works as long as in config where it's a section
(NODE_NOT_IN_PAGE_FLAGS is defined) then there can't be multiple nodes in a
single section.
>> + */
>> + if (page_zone_id(page) != page_zone_id(buddy))
>> + return false;
>> +
>> + VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy);
>> +
>> + return true;
>> +}
>> +
>> +/*
>> * Locate the struct page for both the matching buddy in our
>> * pair (buddy1) and the combined O(n+1) page they form (page).
>> *
>> @@ -234,6 +295,35 @@ __find_buddy_pfn(unsigned long page_pfn,
>> return page_pfn ^ (1 << order);
>> }
>>
>> +/*
>> + * Find the buddy of @page and validate it.
>> + * @page: The input page
>> + * @pfn: The pfn of the page, it saves a call to page_to_pfn() when the
>> + * function is used in the performance-critical __free_one_page().
>> + * @order: The order of the page
>> + * @buddy_pfn: The output pointer to the buddy pfn, it also saves a call to
>> + * page_to_pfn().
>> + *
>> + * The found buddy can be a non PageBuddy, out of @page's zone, or its order is
>> + * not the same as @page. The validation is necessary before use it.
>> + *
>> + * Return: the found buddy page or NULL if not found.
>> + */
>> +static inline struct page *find_buddy_page_pfn(struct page *page,
>> + unsigned long pfn, unsigned int order, unsigned long *buddy_pfn)
>> +{
>> + struct page *buddy;
>> + unsigned long __buddy_pfn = __find_buddy_pfn(pfn, order);
>
> Nit: reverse christmas tree
Was ever reverse xmas tree part of mm/ style or whole Linux styel outside of
net?
