On Tue, Aug 20, 2019 at 03:03:55PM +0800, Wanpeng Li wrote: > Cc Mel Gorman, Kirill, Dave Hansen, > On Tue, 11 Jun 2019 at 07:51, Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> wrote: > > > > On Wed, May 29, 2019 at 04:31:01PM -0700, Mike Kravetz wrote: > > > On 5/28/19 2:49 AM, Wanpeng Li wrote: > > > > Cc Paolo, > > > > Hi all, > > > > On Wed, 14 Feb 2018 at 06:34, Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote: > > > >> > > > >> On 02/12/2018 06:48 PM, Michael Ellerman wrote: > > > >>> Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes: > > > >>> > > > >>>> On Thu, 08 Feb 2018 12:30:45 +0000 Punit Agrawal <punit.agrawal@xxxxxxx> wrote: > > > >>>> > > > >>>>>> > > > >>>>>> So I don't think that the above test result means that errors are properly > > > >>>>>> handled, and the proposed patch should help for arm64. > > > >>>>> > > > >>>>> Although, the deviation of pud_huge() avoids a kernel crash the code > > > >>>>> would be easier to maintain and reason about if arm64 helpers are > > > >>>>> consistent with expectations by core code. > > > >>>>> > > > >>>>> I'll look to update the arm64 helpers once this patch gets merged. But > > > >>>>> it would be helpful if there was a clear expression of semantics for > > > >>>>> pud_huge() for various cases. Is there any version that can be used as > > > >>>>> reference? > > > >>>> > > > >>>> Is that an ack or tested-by? > > > >>>> > > > >>>> Mike keeps plaintively asking the powerpc developers to take a look, > > > >>>> but they remain steadfastly in hiding. > > > >>> > > > >>> Cc'ing linuxppc-dev is always a good idea :) > > > >>> > > > >> > > > >> Thanks Michael, > > > >> > > > >> I was mostly concerned about use cases for soft/hard offline of huge pages > > > >> larger than PMD_SIZE on powerpc. I know that powerpc supports PGD_SIZE > > > >> huge pages, and soft/hard offline support was specifically added for this. > > > >> See, 94310cbcaa3c "mm/madvise: enable (soft|hard) offline of HugeTLB pages > > > >> at PGD level" > > > >> > > > >> This patch will disable that functionality. So, at a minimum this is a > > > >> 'heads up'. If there are actual use cases that depend on this, then more > > > >> work/discussions will need to happen. From the e-mail thread on PGD_SIZE > > > >> support, I can not tell if there is a real use case or this is just a > > > >> 'nice to have'. > > > > > > > > 1GB hugetlbfs pages are used by DPDK and VMs in cloud deployment, we > > > > encounter gup_pud_range() panic several times in product environment. > > > > Is there any plan to reenable and fix arch codes? > > > > > > I too am aware of slightly more interest in 1G huge pages. Suspect that as > > > Intel MMU capacity increases to handle more TLB entries there will be more > > > and more interest. > > > > > > Personally, I am not looking at this issue. Perhaps Naoya will comment as > > > he know most about this code. > > > > Thanks for forwarding this to me, I'm feeling that memory error handling > > on 1GB hugepage is demanded as real use case. > > > > > > > > > In addition, https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/kvm/mmu.c#n3213 > > > > The memory in guest can be 1GB/2MB/4K, though the host-backed memory > > > > are 1GB hugetlbfs pages, after above PUD panic is fixed, > > > > try_to_unmap() which is called in MCA recovery path will mark the PUD > > > > hwpoison entry. The guest will vmexit and retry endlessly when > > > > accessing any memory in the guest which is backed by this 1GB poisoned > > > > hugetlbfs page. We have a plan to split this 1GB hugetblfs page by 2MB > > > > hugetlbfs pages/4KB pages, maybe file remap to a virtual address range > > > > which is 2MB/4KB page granularity, also split the KVM MMU 1GB SPTE > > > > into 2MB/4KB and mark the offensive SPTE w/ a hwpoison flag, a sigbus > > > > will be delivered to VM at page fault next time for the offensive > > > > SPTE. Is this proposal acceptable? > > > > > > I am not sure of the error handling design, but this does sound reasonable. > > > > I agree that that's better. > > > > > That block of code which potentially dissolves a huge page on memory error > > > is hard to understand and I'm not sure if that is even the 'normal' > > > functionality. Certainly, we would hate to waste/poison an entire 1G page > > > for an error on a small subsection. > > > > Yes, that's not practical, so we need at first establish the code base for > > 2GB hugetlb splitting and then extending it to 1GB next. > > I found it is not easy to split. There is a unique hugetlb page size > that is associated with a mounted hugetlbfs filesystem, file remap to > 2MB/4KB will break this. How about hard offline 1GB hugetlb page as > what has already done in soft offline, replace the corrupted 1GB page > by new 1GB page through page migration, the offending/corrupted area > in the original 1GB page doesn't need to be copied into the new page, > the offending/corrupted area in new page can keep full zero just as it > is clear during hugetlb page fault, other sub-pages of the original > 1GB page can be freed to buddy system. The sigbus signal is sent to > userspace w/ offending/corrupted virtual address, and signal code, > userspace should take care this. Splitting hugetlb is simply hard, IMHO. THP splitting is done by years of effort by many great kernel develpers, and I don't think doing similar development on hugetlb is a good idea. I thought of converting hugetlb into thp, but maybe it's not an easy task either. "Hard offlining via soft offlining" approach sounds new and promising to me. I guess we don't need a large patchset to do this. So, thanks for the idea! - Naoya
