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mm/page_alloc.c: do not acquire zone lock in is_free_buddy_page() 

Grabbing zone lock in is_free_buddy_page() gives a wrong sense of
safety, and has potential performance implications when zone is
experiencing lock contention.

In any case, if a caller needs a stable result, it should grab zone lock
before calling this function.

Link: https://lkml.kernel.org/r/20210922152833.4023972-1-eric.dumazet@gmail.com
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Eric Dumazet 2021-11-05 13:40:31 -07:00 committed by Linus Torvalds
parent ebeac3ea99
commit 8446b59baa
1 changed files with 5 additions and 5 deletions
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10
mm/page_alloc.c
View File

@ -9356,21 +9356,21 @@ void __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
}
#endif
/*
* This function returns a stable result only if called under zone lock.
*/
bool is_free_buddy_page(struct page *page)
{
struct zone *zone = page_zone(page);
unsigned long pfn = page_to_pfn(page);
unsigned long flags;
unsigned int order;
spin_lock_irqsave(&zone->lock, flags);
for (order = 0; order < MAX_ORDER; order++) {
struct page *page_head = page - (pfn & ((1 << order) - 1));
if (PageBuddy(page_head) && buddy_order(page_head) >= order)
if (PageBuddy(page_head) &&
buddy_order_unsafe(page_head) >= order)
break;
}
spin_unlock_irqrestore(&zone->lock, flags);
return order < MAX_ORDER;
}