Hi Paolo On Tue, 3 Oct 2023 at 10:46, Paolo Abeni <pabeni@xxxxxxxxxx> wrote: > > 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@xxxxxxxxxx/ > > 2. https://lore.kernel.org/all/20230818145145.4b357c89@xxxxxxxxxx/ > > > > Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> > > Signed-off-by: Yunsheng Lin <linyunsheng@xxxxxxxxxx> > > CC: Lorenzo Bianconi <lorenzo@xxxxxxxxxx> > > CC: Alexander Duyck <alexander.duyck@xxxxxxxxx> > > CC: Liang Chen <liangchen.linux@xxxxxxxxx> > > CC: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx> > > CC: Guillaume Tucker <guillaume.tucker@xxxxxxxxxxxxx> > > CC: Matthew Wilcox <willy@xxxxxxxxxxxxx> > > CC: Linux-MM <linux-mm@xxxxxxxxx> > > --- > > 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. I am trying! Unfortunately, it's this time of the year when I have to travel a lot. I'll be back in 15 days from now and I will be able to have a look Thanks and sorry for the delay /Ilias > > Cheers, > > Paolo >
