| Message ID | 20191118082003.26240-1-richardw.yang@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/2] mm/memory-failure.c: PageHuge is handled at the beginning of memory_failure | expand |
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?
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. >-- > >Thanks, > >David / dhildenb
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>
On Wed, Nov 20, 2019 at 04:04:44PM +0100, David Hildenbrand wrote: >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 > That's very helpful. Thanks for your time sincerely. >Reviewed-by: David Hildenbrand <david@redhat.com> > >-- > >Thanks, > >David / dhildenb
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
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(-)