Re: [PATCH v2 00/19] mm: Support huge pfnmaps

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Adding Ankit in case he has opinions.

On Tue, Aug 27, 2024 at 5:42 PM Jiaqi Yan <jiaqiyan@xxxxxxxxxx> wrote:
>
> On Tue, Aug 27, 2024 at 3:57 PM Peter Xu <peterx@xxxxxxxxxx> wrote:
> >
> > On Tue, Aug 27, 2024 at 03:36:07PM -0700, Jiaqi Yan wrote:
> > > Hi Peter,
> >
> > Hi, Jiaqi,
> >
> > > I am curious if there is any work needed for unmap_mapping_range? If a
> > > driver hugely remap_pfn_range()ed at 1G granularity, can the driver
> > > unmap at PAGE_SIZE granularity? For example, when handling a PFN is
> >
> > Yes it can, but it'll invoke the split_huge_pud() which default routes to
> > removal of the whole pud right now (currently only covers either DAX
> > mappings or huge pfnmaps; it won't for anonymous if it comes, for example).
> >
> > In that case it'll rely on the driver providing proper fault() /
> > huge_fault() to refault things back with smaller sizes later when accessed
> > again.
>
> I see, so the driver needs to drive the recovery process, and code
> needs to be in the driver.
>
> But it seems to me the recovery process will be more or less the same
> to different drivers? In that case does it make sense that
> memory_failure do the common things for all drivers?
>
> Instead of removing the whole pud, can driver or memory_failure do
> something similar to non-struct-page-version of split_huge_page? So
> driver doesn't need to re-fault good pages back?
>
>
> >
> > > poisoned in the 1G mapping, it would be great if the mapping can be
> > > splitted to 2M mappings + 4k mappings, so only the single poisoned PFN
> > > is lost. (Pretty much like the past proposal* to use HGM** to improve
> > > hugetlb's memory failure handling).
> >
> > Note that we're only talking about MMIO mappings here, in which case the
> > PFN doesn't even have a struct page, so the whole poison idea shouldn't
> > apply, afaiu.
>
> Yes, there won't be any struct page. Ankit proposed this patchset* for
> handling poisoning. I wonder if someday the vfio-nvgrace-gpu-pci
> driver adopts your change via new remap_pfn_range (install PMD/PUD
> instead of PTE), and memory_failure_pfn still
> unmap_mapping_range(pfn_space->mapping, pfn << PAGE_SHIFT, PAGE_SIZE,
> 0), can it somehow just work and no re-fault needed?
>
> * https://lore.kernel.org/lkml/20231123003513.24292-2-ankita@xxxxxxxxxx/#t
>
>
>
> >
> > Thanks,
> >
> > --
> > Peter Xu
> >





[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]

  Powered by Linux