mm: optimize compound_head() by avoiding a shared page flag
The patch adds PageTail(page) and PageHead(page) to check if a page is the head or the tail of a compound page. This is done by masking the two bits describing the state of a compound page and then comparing them. So one comparision and a branch instead of two bit checks and two branches. Signed-off-by: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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