Re: [PATCH] mm/vmalloc: do not output a spurious warning when huge vmalloc() fails

[Vlastimil Babka]

On 6/5/23 22:11, Lorenzo Stoakes wrote:
> In __vmalloc_area_node() we always warn_alloc() when an allocation
> performed by vm_area_alloc_pages() fails unless it was due to a pending
> fatal signal.
> 
> However, huge page allocations instigated either by vmalloc_huge() or
> __vmalloc_node_range() (or a caller that invokes this like kvmalloc() or
> kvmalloc_node()) always falls back to order-0 allocations if the huge page
> allocation fails.
> 
> This renders the warning useless and noisy, especially as all callers
> appear to be aware that this may fallback. This has already resulted in at
> least one bug report from a user who was confused by this (see link).
> 
> Therefore, simply update the code to only output this warning for order-0
> pages when no fatal signal is pending.
> 
> Link: https://bugzilla.suse.com/show_bug.cgi?id=1211410
> Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>

I think there are more reports of same thing from the btrfs context, that
appear to be a 6.3 regression

https://bugzilla.kernel.org/show_bug.cgi?id=217466
Link: https://lore.kernel.org/all/efa04d56-cd7f-6620-bca7-1df89f49bf4b@xxxxxxxxx/

If this indeed helps, it would make sense to Cc: stable here. Although I
don't see what caused the regression, the warning itself is not new, so is
it new source of order-9 attempts in vmalloc() or new reasons why order-9
pages would not be possible to allocate?

> ---
>  mm/vmalloc.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index ab606a80f475..e563f40ad379 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3149,11 +3149,20 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
>  	 * allocation request, free them via vfree() if any.
>  	 */
>  	if (area->nr_pages != nr_small_pages) {
> -		/* vm_area_alloc_pages() can also fail due to a fatal signal */
> -		if (!fatal_signal_pending(current))
> +		/*
> +		 * vm_area_alloc_pages() can fail due to insufficient memory but
> +		 * also:-
> +		 *
> +		 * - a pending fatal signal
> +		 * - insufficient huge page-order pages
> +		 *
> +		 * Since we always retry allocations at order-0 in the huge page
> +		 * case a warning for either is spurious.
> +		 */
> +		if (!fatal_signal_pending(current) && page_order == 0)
>  			warn_alloc(gfp_mask, NULL,
> -				"vmalloc error: size %lu, page order %u, failed to allocate pages",
> -				area->nr_pages * PAGE_SIZE, page_order);
> +				"vmalloc error: size %lu, failed to allocate pages",
> +				area->nr_pages * PAGE_SIZE);
>  		goto fail;
>  	}
>