Re: [RFC PATCH v5 2/4] mm: distinguish large folio swap allocation failures

["David Hildenbrand (Arm)" <david@kernel.org>]

On 7/30/26 14:23, Xueyuan Chen wrote:
> folio_alloc_swap() reports most allocation failures with a generic
> negative error code. Reclaim cannot tell whether splitting a large folio
> could make progress or whether there is no backing space at all.
> 
> Keep the global free swap count and the remaining hierarchical memcg swap
> margin as separate inputs. The memcg charge path reports only its own
> margin; folio_alloc_swap() combines the two layers when classifying an
> allocation failure.
> 
> Return -E2BIG for large folios when a smaller allocation might still fit,
> -ENOSPC when no global swap space is available, and -ENOMEM when the
> failure is not helped by splitting.
> 
> For early large-folio rejections, check global and memcg swap availability
> instead of returning -E2BIG unconditionally. On a memcg charge failure,
> swap slot allocation has already succeeded, so use the remaining memcg
> margin to decide whether a smaller charge might fit.
> 
> This only refines folio_alloc_swap() return codes. The reclaim callers are
> updated separately.
> 
> Suggested-by: Barry Song <baohua@kernel.org>
> Suggested-by: Youngjun Park <youngjun.park@lge.com>
> Signed-off-by: Xueyuan Chen <xueyuan.chen21@gmail.com>
> ---
>  include/linux/swap.h | 16 ++++++++++++----
>  mm/memcontrol.c      | 32 +++++++++++++++++++++++++++++++-
>  mm/swapfile.c        | 32 ++++++++++++++++++++++++--------
>  3 files changed, 67 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 0544b2ec4c56..7d12058174ae 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -509,12 +509,13 @@ static inline void folio_throttle_swaprate(struct folio *folio, gfp_t gfp)
>  #endif
>  
>  #if defined(CONFIG_MEMCG) && defined(CONFIG_SWAP)
> -int __mem_cgroup_try_charge_swap(struct folio *folio);
> -static inline int mem_cgroup_try_charge_swap(struct folio *folio)
> +int __mem_cgroup_try_charge_swap(struct folio *folio, long *swap_margin);
> +static inline int mem_cgroup_try_charge_swap(struct folio *folio,
> +					     long *swap_margin)

Nit: two tab indent

[...]

> -static inline int mem_cgroup_try_charge_swap(struct folio *folio)
> +static inline int mem_cgroup_try_charge_swap(struct folio *folio,
> +					     long *swap_margin)


Nothing else jumped at me

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David