On 02.12.19 23:28, Wei Yang wrote: > On Wed, Nov 20, 2019 at 04:07:38PM +0100, David Hildenbrand wrote: >> On 18.11.19 09:20, Wei Yang wrote: >>> hpage is not changed. >>> >>> Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx> >>> --- >>> mm/memory-failure.c | 1 - >>> 1 file changed, 1 deletion(-) >>> >>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c >>> index 392ac277b17d..9784f4339ae7 100644 >>> --- a/mm/memory-failure.c >>> +++ b/mm/memory-failure.c >>> @@ -1319,7 +1319,6 @@ int memory_failure(unsigned long pfn, int flags) >>> } >>> unlock_page(p); >>> VM_BUG_ON_PAGE(!page_count(p), p); >>> - hpage = compound_head(p); >>> } >>> /* >>> >> >> I am *absolutely* no transparent huge page expert (sorry :) ), but won't the >> split_huge_page(p) eventually split the compound page, such that >> compound_head(p) will return something else after that call? >> > > Hi, David > > Took sometime to look into the code and re-think about it. Found maybe we can > simplify this in another way. > > First, code touches here means split_huge_page() succeeds and "p" is now a PTE > page. So compound_head(p) == p. While this would also be my intuition, I can't state that this is guaranteed to be the case (IOW, I did not check the code/documentation) :) > > Then let's look at who will use hpage in the following function. There are two > uses in current upstream: > > * page_flags calculation > * hwpoison_user_mappings() > > The first one would be removed in next patch since PageHuge is handled at the > beginning. > > And in the second place, comment says if split succeeds, hpage points to page > "p". > > After all, we don't need to re-calculate hpage after split, and just replace > hpage in hwpoison_user_mappings() with p is enough. That assumption would only be true in case all compound pages at this point are transparent huge pages, no? AFAIK that is not necessarily true. Or am I missing something? -- Thanks, David / dhildenb
