Messages in this thread | | | Subject | Re: [PATCH net-next v10 1/6] page_pool: fragment API support for 32-bit arch with 64-bit DMA | From | Paolo Abeni <> | Date | Tue, 03 Oct 2023 09:45:56 +0200 |
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On Fri, 2023-09-22 at 17:11 +0800, Yunsheng Lin wrote: > Currently page_pool_alloc_frag() is not supported in 32-bit > arch with 64-bit DMA because of the overlap issue between > pp_frag_count and dma_addr_upper in 'struct page' for those > arches, which seems to be quite common, see [1], which means > driver may need to handle it when using fragment API. > > It is assumed that the combination of the above arch with an > address space >16TB does not exist, as all those arches have > 64b equivalent, it seems logical to use the 64b version for a > system with a large address space. It is also assumed that dma > address is page aligned when we are dma mapping a page aligned > buffer, see [2]. > > That means we're storing 12 bits of 0 at the lower end for a > dma address, we can reuse those bits for the above arches to > support 32b+12b, which is 16TB of memory. > > If we make a wrong assumption, a warning is emitted so that > user can report to us. > > 1. https://lore.kernel.org/all/20211117075652.58299-1-linyunsheng@huawei.com/ > 2. https://lore.kernel.org/all/20230818145145.4b357c89@kernel.org/ > > Signed-off-by: Jakub Kicinski <kuba@kernel.org> > Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com> > CC: Lorenzo Bianconi <lorenzo@kernel.org> > CC: Alexander Duyck <alexander.duyck@gmail.com> > CC: Liang Chen <liangchen.linux@gmail.com> > CC: Alexander Lobakin <aleksander.lobakin@intel.com> > CC: Guillaume Tucker <guillaume.tucker@collabora.com> > CC: Matthew Wilcox <willy@infradead.org> > CC: Linux-MM <linux-mm@kvack.org> > --- > include/linux/mm_types.h | 13 +------------ > include/net/page_pool/helpers.h | 20 ++++++++++++++------ > net/core/page_pool.c | 14 +++++++++----- > 3 files changed, 24 insertions(+), 23 deletions(-) > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 36c5b43999e6..74b49c4c7a52 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -125,18 +125,7 @@ struct page { > struct page_pool *pp; > unsigned long _pp_mapping_pad; > unsigned long dma_addr; > - union { > - /** > - * dma_addr_upper: might require a 64-bit > - * value on 32-bit architectures. > - */ > - unsigned long dma_addr_upper; > - /** > - * For frag page support, not supported in > - * 32-bit architectures with 64-bit DMA. > - */ > - atomic_long_t pp_frag_count; > - }; > + atomic_long_t pp_frag_count; > }; > struct { /* Tail pages of compound page */ > unsigned long compound_head; /* Bit zero is set */
As noted by Jesper, since this is touching the super-critcal struct page, an explicit ack from the mm people is required.
@Matthew: could you please have a look?
I think it would be nice also an explicit ack from Jesper and/or Ilias.
Cheers,
Paolo
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