Hugepage migration

[Baruch Even]

I have tested the MAP_LOCKED, it doesn't help in this case. I do intend to
report to the kernel but was wondering if others have hit upon this first.

On Tue, May 30, 2023 at 4:35 AM Stephen Hemminger <
stephen at networkplumber.org> wrote:

> On Sun, 28 May 2023 23:07:40 +0300
> Baruch Even <baruch at weka.io> wrote:
>
> > Hi,
> >
> > We found an issue with newer kernels (5.13+) that are found on newer OSes
> > (Ubuntu22, Rocky9, Ubuntu20 with kernel 5.15) where a 2M page that was
> > allocated for DPDK was migrated (moved into another physical page) when a
> > 1G page was allocated.
> >
> > From our reading of the kernel commits this started with commit
> > ae37c7ff79f1f030e28ec76c46ee032f8fd07607
> >     mm: make alloc_contig_range handle in-use hugetlb pages
> >
> > This caused what looked like memory corruptions to us and cases where the
> > rings were moved from their physical location and communication was no
> > longer possible.
> >
> > I wanted to ask if anyone else hit this issue and what mitigations are
> > available?
> >
> > We are currently looking at using a kernel driver to pin the pages but I
> > expect that this issue will affect others and that a more general
> approach
> > is needed.
> >
> > Thanks,
> > Baruch
> >
>
> Fix might be as simple as asking kernel to lock the mmap().
>
> diff --git a/lib/eal/linux/eal_hugepage_info.c
> b/lib/eal/linux/eal_hugepage_info.c
> index 581d9dfc91eb..989c69387233 100644
> --- a/lib/eal/linux/eal_hugepage_info.c
> +++ b/lib/eal/linux/eal_hugepage_info.c
> @@ -48,7 +48,8 @@ map_shared_memory(const char *filename, const size_t
> mem_size, int flags)
>                 return NULL;
>         }
>         retval = mmap(NULL, mem_size, PROT_READ | PROT_WRITE,
> -                       MAP_SHARED, fd, 0);
> +                       MAP_SHARED_VALIDATE | MAP_LOCKED, fd, 0);
> +
>         close(fd);
>         return retval == MAP_FAILED ? NULL : retval;
>  }
>


-- 
Baruch Even
Platform Technical Lead,  WEKA
E baruch at weka.io* ­*W www.weka.io
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