Re: [syzbot] [mm?] WARNING in xfs_init_fs_context

[Vlastimil Babka]

On 9/29/25 08:40, Christoph Hellwig wrote:
> This looks like slub turning a < PAGE_SIZE allocation into a order > 0
> folio allocation, which the page allocator then complains about.

It's order-1 to order-2 but in principle yes.

> We'll either need to make slab not propagate < PAGE_SIZE allocations
> to order > 0 page allocation

It normally doesn't, but enabling debugging stuff can do that. In this case
it seems to be KASAN, but could be also slub's own redzones etc.

, or make the page allocator handle the
> latter.

It handles it, but warns you're doing something you shouldn't, as
__GFP_NOFAIL allocations shouldn't be large. We could just silence it if
it's due to debugging. SLUB could check if page allocation is bloated due to
debugging and there's __GFP_NOFAIL, and then add an extra gfp flag to
silence the warning. We could use __GFP_NOWARN with the risk of someone else
combining __GFP_NOFAIL and __GFP_NOWARN to silence this. Or invent some
other internal flag, but there's not many bits left.

> And XFS shouldn't need the NOFAIL allocation here, but this will break
> things elsewhere as well.
>