Messages in this thread | | | Subject | Re: isolate_lru_page on !head pages | From | Vlastimil Babka <> | Date | Tue, 22 Dec 2015 16:47:39 +0100 |
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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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