Messages in this thread | | | Subject | Re: [PATCH 1/2] mm/memory-failure.c: PageHuge is handled at the beginning of memory_failure | From | David Hildenbrand <> | Date | Wed, 20 Nov 2019 16:04:44 +0100 |
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On 20.11.19 01:46, Wei Yang wrote: > On Tue, Nov 19, 2019 at 01:23:54PM +0100, David Hildenbrand wrote: >> On 18.11.19 09:20, Wei Yang wrote: >>> PageHuge is handled by memory_failure_hugetlb(), so this case could be >>> removed. >>> >>> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com> >>> --- >>> mm/memory-failure.c | 5 +---- >>> 1 file changed, 1 insertion(+), 4 deletions(-) >>> >>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c >>> index 3151c87dff73..392ac277b17d 100644 >>> --- a/mm/memory-failure.c >>> +++ b/mm/memory-failure.c >>> @@ -1359,10 +1359,7 @@ int memory_failure(unsigned long pfn, int flags) >>> * page_remove_rmap() in try_to_unmap_one(). So to determine page status >>> * correctly, we save a copy of the page flags at this time. >>> */ >>> - if (PageHuge(p)) >>> - page_flags = hpage->flags; >>> - else >>> - page_flags = p->flags; >>> + page_flags = p->flags; >>> /* >>> * unpoison always clear PG_hwpoison inside page lock >>> >> >> I somewhat miss a proper explanation why this is safe to do. We access page >> flags here, so why is it safe to refer to the ones of the sub-page? >> > > Hi, David > > I think your comment is on this line: > > page_flags = p->flags; > > Maybe we need to use this: > > page_flags = hpage->flags; > > And use hpage in the following or even the whole function? > > While one thing interesting is not all "compound page" is PageCompound. For > some sub-page, we can't get the correct head. This means we may just check on > the sub-page.
Oh wait, I think I missed the check right at the beginning of this function, sorry :/
Sooo, memory_failure_hugetlb() was introduced by
commit 761ad8d7c7b5485bb66fd5bccb58a891fe784544 Author: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Date: Mon Jul 10 15:47:47 2017 -0700
mm: hwpoison: introduce memory_failure_hugetlb()
and essentially ripped out all PageHuge() checks *except* this check. This check was introduced in
commit 7258ae5c5a2ce2f5969e8b18b881be40ab55433d Author: James Morse <james.morse@arm.com> Date: Fri Jun 16 14:02:29 2017 -0700
mm/memory-failure.c: use compound_head() flags for huge pages
Maybe that was just a merge oddity as both commits are only ~1month apart. IOW, I think Naoya's patch forgot to rip it out.
Can we make this clear in the patch description like "This is dead code that cannot be reached after commit 761ad8d7c7b5 ("mm: hwpoison: introduce memory_failure_hugetlb()")"
I assume Andrew can fix up when applying
Reviewed-by: David Hildenbrand <david@redhat.com>
--
Thanks,
David / dhildenb
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