On 12/15/2015 05:59 PM, Michal Hocko wrote:
head page is what linked into LRU, but not nessesary the way we obtain the
page to check. If we check PageLRU(pte_page(*pte)) it should produce the
right result.
I am not following you here. Any pfn walk could get to a tail page and
if we happen to do e.g. isolate_lru_page we have to remember that we
should always treat compound page differently. This is subtle.
I think the problem is that isolate_lru_page() is not the only reason
for calling PageLRU(). And the other use cases have different
expectations, to either way (PF_ANY or PF_HEAD) you pick for PageLRU(),
somebody will have to be careful. IMHO usually it's pfn scanners who
have to be careful for many reasons...
Anyway I
am far from understading other parts of the refcount rework so I will
spend time studying the code as soon as the time permits. In the
meantime I agree that VM_BUG_ON_PAGE(PageTail(page), page) would be
useful to catch all the fallouts.
+1
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