linux-kernel - RE: [PATCH net,v2] net: mana: Switch to page pool for jumbo frames

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Message-ID:
 <SA6PR21MB423173F0DB9FE874F4F02966CEA72@SA6PR21MB4231.namprd21.prod.outlook.com>
Date: Tue, 25 Mar 2025 18:32:52 +0000
From: Long Li <longli@...rosoft.com>
To: Haiyang Zhang <haiyangz@...rosoft.com>, "linux-hyperv@...r.kernel.org"
	<linux-hyperv@...r.kernel.org>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>
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Subject: RE: [PATCH net,v2] net: mana: Switch to page pool for jumbo frames

> > > Subject: [PATCH net,v2] net: mana: Switch to page pool for jumbo
> > > frames
> > >
> > > Frag allocators, such as netdev_alloc_frag(), were not designed to
> > > work
> > for
> > > fragsz > PAGE_SIZE.
> > >
> > > So, switch to page pool for jumbo frames instead of using page frag
> > allocators.
> > > This driver is using page pool for smaller MTUs already.
> > >
> > > Cc: stable@...r.kernel.org
> > > Fixes: 80f6215b450e ("net: mana: Add support for jumbo frame")
> > > Signed-off-by: Haiyang Zhang <haiyangz@...rosoft.com>

Reviewed-by: Long Li <longli@...rosoft.com>

> > > ---
> > > v2: updated the commit msg as suggested by Jakub Kicinski.
> > >
> > > ---
> > >  drivers/net/ethernet/microsoft/mana/mana_en.c | 46
> > > ++++---------------
> > >  1 file changed, 9 insertions(+), 37 deletions(-)
> > >
> > > diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c
> > > b/drivers/net/ethernet/microsoft/mana/mana_en.c
> > > index 9a8171f099b6..4d41f4cca3d8 100644
> > > --- a/drivers/net/ethernet/microsoft/mana/mana_en.c
> > > +++ b/drivers/net/ethernet/microsoft/mana/mana_en.c
> > > @@ -661,30 +661,16 @@ int mana_pre_alloc_rxbufs(struct
> > > mana_port_context *mpc, int new_mtu, int num_qu
> > >   mpc->rxbpre_total = 0;
> > >
> > >   for (i = 0; i < num_rxb; i++) {
> > > -         if (mpc->rxbpre_alloc_size > PAGE_SIZE) {
> > > -                 va = netdev_alloc_frag(mpc->rxbpre_alloc_size);
> > > -                 if (!va)
> > > -                         goto error;
> > > -
> > > -                 page = virt_to_head_page(va);
> > > -                 /* Check if the frag falls back to single page */
> > > -                 if (compound_order(page) <
> > > -                     get_order(mpc->rxbpre_alloc_size)) {
> > > -                         put_page(page);
> > > -                         goto error;
> > > -                 }
> > > -         } else {
> > > -                 page = dev_alloc_page();
> > > -                 if (!page)
> > > -                         goto error;
> > > +         page = dev_alloc_pages(get_order(mpc->rxbpre_alloc_size));
> > > +         if (!page)
> > > +                 goto error;
> > >
> > > -                 va = page_to_virt(page);
> > > -         }
> > > +         va = page_to_virt(page);
> > >
> > >           da = dma_map_single(dev, va + mpc->rxbpre_headroom,
> > >                               mpc->rxbpre_datasize, DMA_FROM_DEVICE);
> > >           if (dma_mapping_error(dev, da)) {
> > > -                 put_page(virt_to_head_page(va));
> > > +                 put_page(page);
> >
> > Should we use __free_pages()?
>
> Quote from doc:
> https://www.ker/
> nel.org%2Fdoc%2Fhtml%2Fnext%2Fcore-api%2Fmm-
> api.html&data=05%7C02%7Clongli%40microsoft.com%7Cada2b7bad76e4ab7286
> 508dd6bc87430%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C638785
> 230869082534%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIl
> YiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C
> 0%7C%7C%7C&sdata=VINKfrv80MzhE1mmibv1RrRz4WCmr%2BZhWDf1ZaOv47
> w%3D&reserved=0
> ___free_pages():
> "This function can free multi-page allocations that are not compound pages."
> "If you want to use the page's reference count to decide when to free the
> allocation, you should allocate a compound page, and use put_page() instead of
> __free_pages()."
>
> And, since dev_alloc_pages returns compound page for high order page, we use
> put_page() which works for both compound & single page.
>
> Thanks,
> - Haiyang