Re: [PATCH 1/2] mm: hugetlb: Return -ENOSPC on memcg charge failure

[Joshua Hahn <joshua.hahnjy@gmail.com>]

On Wed, 02 Sep 2026 01:22:56 -0700 Ackerley Tng via B4 Relay <devnull+ackerleytng.google.com@kernel.org> wrote:

> From: Ackerley Tng <ackerleytng@google.com>
> 
> When mem_cgroup_charge_hugetlb() fails with -ENOMEM, alloc_hugetlb_folio()
> currently propagates this error. This results in the page fault handler
> returning VM_FAULT_OOM.
> 
> Because HugeTLB allocations are high-order and use __GFP_RETRY_MAYFAIL,
> they bypass the OOM killer. Returning VM_FAULT_OOM to the #PF handler
> without triggering the OOM killer (or having it make progress) leads to
> an infinite loop of retrying the fault.
> 
> Avoid this loop by returning -ENOSPC when charging fails, which maps to
> VM_FAULT_SIGBUS, terminating the process cleanly.
> 
> Make mem_cgroup_charge_hugetlb() fault handling use a common error handling
> path, the same handling used for hugetlb_cgroup_uncharge_cgroup{,_rsvd}(),
> which also don't trigger the OOM killer and hence opt to terminate the
> process with a SIGBUS.

Hi Ackerley,

I hope you are doing well! IIRC, this is the same fix as the one in
[1] (in spirit) right? 

I prefer this change since it is more obvious that we return
-ENOSPC right there and then. Since this is a fix please feel free to
add:

Reviewed-by: Joshua Hahn <joshua.hahnjy@gmail.com>

> Fixes: 991135774c0e0 ("memcg/hugetlb: introduce mem_cgroup_charge_hugetlb")
> Cc: stable@vger.kernel.org
> Signed-off-by: Ackerley Tng <ackerleytng@google.com>
> ---
>  mm/hugetlb.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 7857728457952..01b57f6d3b804 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2823,7 +2823,6 @@ void wait_for_freed_hugetlb_folios(void)
>   *
>   * Return: A pointer to the allocated folio, or an ERR_PTR on failure.
>   *         -ENOSPC if cgroup charging fails or no folio is available.
> - *         -ENOMEM if mem cgroup charging fails.
>   */
>  struct folio *hugetlb_alloc_folio(struct hstate *h,
>  		struct mempolicy_interpreted *mpoli, u8 alloc_flags)
> @@ -2896,7 +2895,18 @@ struct folio *hugetlb_alloc_folio(struct hstate *h,
>  		 * were committed to the folio and freeing the folio
>  		 * would have cleared those up.
>  		 */
> -		return ERR_PTR(ret);
> +		/*
> +		 * Return -ENOSPC when this function fails to allocate
> +		 * or charge a huge page. If a standard (PAGE_SIZE)
> +		 * page allocation fails, the OOM killer is given a
> +		 * chance to run, which may resolve the failure on
> +		 * retry. However, for HugeTLB allocations, the OOM
> +		 * killer is not triggered.  Returning -ENOMEM (or
> +		 * anything resulting in VM_FAULT_OOM) would leak to
> +		 * the #PF handler, causing it to loop indefinitely
> +		 * retrying the fault.
> +		 */

NIT: I do feel like this comment block is a bit verbose, though. We just
want to explain why we return -ENOSPC rather than -ENOMEM, maybe we can
just explain that OOM killer not triggered --> retrying is futile?

The change itself looks good though : -) and I don't want to block the
fix. We can change the comment later.

> +		return ERR_PTR(-ENOSPC);
>  	}
>  
>  	return folio;
> 
> -- 
> 2.55.0.970.g62bdec98f9-goog

[1] https://lore.kernel.org/linux-mm/20260720-hugetlb-alloc-failure-fixes-v3-2-7d2a169aa9ee@google.com/