Re: [PATCH 2/3] mm: support fallible mempool_alloc_bulk()

[Christoph Hellwig]

On Mon, Aug 10, 2026 at 09:14:04AM -0700, Eric Biggers wrote:
> On Mon, Aug 10, 2026 at 09:00:11AM -0700, Christoph Hellwig wrote:
> > On Thu, Aug 06, 2026 at 03:10:30PM -0700, Eric Biggers wrote:
> > > To fix a deadlock, blk-crypto-fallback needs to be able to make fallible
> > > mempool_alloc_bulk() allocations.
> > 
> > It doesn't.  fallible mempool allocations are a concept that doesn't
> > make much sense.  Please just go straight to the backing page allocator
> > instead for callers that do not need the mempool guarantees.
> 
> It does make sense.  When alloc_pages_bulk() doesn't completely succeed,
> there still might be pages available in the mempool.

But they should not go to a caller that does not need the mempool.

> blk_crypto_alloc_enc_bio() should try to take them before falling back
> to scheduling the rescuer kworker.  The rescuer encounters scheduling
> overhead and is single-threaded, so it's slow and should be used only
> when absolutely necessary.

No, it should just try a regular non-bulk alloc_pages (and eventually
alloc_pages_bulk should do that fallback for the callers, but that's
a separate discussion).