Re: [PATCH iwl-next v3 0/2] libeth, idpf: use GFP_KERNEL for the initial Rx ring fill

[Luigi Rizzo]

On Thu, Nov 5, 2026 at 7:08 PM Alexander Lobakin
<aleksander.lobakin@xxxxxxxxx> wrote:
>
> From: Luigi Rizzo <lrizzo@xxxxxxxxxx>
> Date: Tue,  3 Nov 2026 16:23:23 +0000
>
> > libeth_rx_alloc() always allocates with GFP_ATOMIC, including when a
> > driver fills its Rx rings at open or on queue reconfiguration. That
> > fill runs in process context, right after page_pool_create() and before
> > the queues' NAPI is enabled, so it may sleep, and GFP_ATOMIC is
> > needlessly restrictive there: it can neither reclaim nor compact, while
> > the initial fill can allocate tens of thousands of buffers across all
> > queues.
> >
> > Patch 1 adds __libeth_rx_alloc() taking a gfp_t parameter and turns
> > libeth_rx_alloc() into its GFP_ATOMIC wrapper.
> > Patch 2 switches idpf's initial Rx ring fill (both splitq and singleq)
> > to GFP_KERNEL.
> >
> > v3:
> >   - rename libeth_rx_alloc_gfp() to __libeth_rx_alloc() and put the gfp
> >     argument on its own line in page_pool_alloc_netmem() (Alexander Lobakin)
> > v2: https://lore.kernel.org/r/20261019210604.2433620-1-lrizzo@xxxxxxxxxx/
> >   - split into two patches (libeth helper and idpf consumer)
> > v1: https://lore.kernel.org/r/20261016151835.2500807-1-lrizzo@xxxxxxxxxx/
> >
> > Luigi Rizzo (2):
> >   libeth: add __libeth_rx_alloc() to specify allocation flags
> >   idpf: use GFP_KERNEL for the initial Rx ring fill
>
> For the series:
>
> Reviewed-by: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx>

Looking further at the problem, gemini pointed out that libeth_rx_alloc()
is called in a way that makes it easy and robust to tell when it
can use GFP_KERNEL. This would greatly simplify the patch.

Alexander, do you like this version better perhaps ?

cheers
luigi

diff --git a/include/net/libeth/rx.h b/include/net/libeth/rx.h
index 5d991404845e6..38c0e5066f0ef 100644
--- a/include/net/libeth/rx.h
+++ b/include/net/libeth/rx.h
@@ -104,10 +104,17 @@ void libeth_rx_fq_destroy(struct libeth_fq *fq);
 static inline dma_addr_t libeth_rx_alloc(const struct libeth_fq_fp *fq, u32 i)
 {
        struct libeth_fqe *buf = &fq->fqes[i];
+       /* fq->fqes is zero-allocated and pre-filled in process context for
+        * indices [0 .. fq->count - 2]; slot fq->count - 1 is first allocated
+        * in NAPI. Use GFP_KERNEL for initial pre-fill and GFP_ATOMIC after.
+        */
+       gfp_t gfp = (buf->truesize || i == fq->count - 1) ?
+                   GFP_ATOMIC : GFP_KERNEL;

        buf->truesize = fq->truesize;
-       buf->netmem = page_pool_dev_alloc_netmem(fq->pp, &buf->offset,
-                                                &buf->truesize);
+       buf->netmem = page_pool_alloc_netmem(fq->pp, &buf->offset,
+                                            &buf->truesize,
+                                            gfp | __GFP_NOWARN);
        if (unlikely(!buf->netmem))
                return DMA_MAPPING_ERROR;

>
> Thanks!
> Olek