From: Matthew Wilcox <willy@infradead.org>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Arnd Bergmann <arnd@kernel.org>,
Grygorii Strashko <grygorii.strashko@ti.com>,
netdev <netdev@vger.kernel.org>,
Ilias Apalodimas <ilias.apalodimas@linaro.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"open list:BROADCOM NVRAM DRIVER" <linux-mips@vger.kernel.org>,
Michal Hocko <mhocko@kernel.org>, Linux MM <linux-mm@kvack.org>,
Mel Gorman <mgorman@suse.de>,
Jesper Dangaard Brouer <brouer@redhat.com>,
mcroce@linux.microsoft.com,
arcml <linux-snps-arc@lists.infradead.org>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Christoph Hellwig <hch@lst.de>,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 1/2] mm: Fix struct page layout on 32-bit systems
Date: Tue, 20 Apr 2021 12:32:16 +0100 [thread overview]
Message-ID: <20210420113216.GA3596236@casper.infradead.org> (raw)
In-Reply-To: <CAMuHMdXm1Zg=Wm-=tn5jUJwqVGUvCi5yDaW0PXWC2DEDYGcy5A@mail.gmail.com>
On Tue, Apr 20, 2021 at 09:39:54AM +0200, Geert Uytterhoeven wrote:
> > +++ b/include/linux/mm_types.h
> > @@ -97,10 +97,10 @@ struct page {
> > };
> > struct { /* page_pool used by netstack */
> > /**
> > - * @dma_addr: might require a 64-bit value even on
> > + * @dma_addr: might require a 64-bit value on
> > * 32-bit architectures.
> > */
> > - dma_addr_t dma_addr;
> > + unsigned long dma_addr[2];
>
> So we get two 64-bit words on 64-bit platforms, while only one is
> needed?
Not really. This is part of the 5-word union in struct page, so the space
ends up being reserved anyway, event if it's not "assigned" to dma_addr.
> > + dma_addr_t ret = page->dma_addr[0];
> > + if (sizeof(dma_addr_t) > sizeof(unsigned long))
> > + ret |= (dma_addr_t)page->dma_addr[1] << 16 << 16;
>
> We don't seem to have a handy macro for a 32-bit left shift yet...
>
> But you can also avoid the warning using
>
> ret |= (u64)page->dma_addr[1] << 32;
Sure. It doesn't really matter which way we eliminate the warning;
the code is unreachable.
> > +{
> > + page->dma_addr[0] = addr;
> > + if (sizeof(dma_addr_t) > sizeof(unsigned long))
> > + page->dma_addr[1] = addr >> 16 >> 16;
>
> ... but we do have upper_32_bits() for a 32-bit right shift.
Yep, that's what my current tree looks like.
next prev parent reply other threads:[~2021-04-20 11:33 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-16 23:07 [PATCH 0/2] Change struct page layout for page_pool Matthew Wilcox (Oracle)
2021-04-16 23:07 ` [PATCH 1/2] mm: Fix struct page layout on 32-bit systems Matthew Wilcox (Oracle)
2021-04-17 1:08 ` kernel test robot
2021-04-17 2:45 ` Matthew Wilcox
2021-04-17 18:32 ` Ilias Apalodimas
2021-04-17 20:22 ` Matthew Wilcox
2021-04-18 11:21 ` Ilias Apalodimas
2021-04-17 21:18 ` David Laight
2021-04-17 22:45 ` Matthew Wilcox
2021-04-20 2:48 ` Vineet Gupta
2021-04-20 3:10 ` Matthew Wilcox
2021-04-20 7:07 ` Arnd Bergmann
2021-04-20 21:14 ` Vineet Gupta
2021-04-20 21:20 ` Arnd Bergmann
2021-04-21 5:50 ` hch
2021-04-21 8:43 ` David Laight
2021-04-21 8:58 ` Arnd Bergmann
2021-04-20 7:39 ` Geert Uytterhoeven
2021-04-20 8:39 ` David Laight
2021-04-20 11:32 ` Matthew Wilcox [this message]
2021-04-17 7:34 ` Jesper Dangaard Brouer
2021-04-20 7:21 ` Rasmus Villemoes
2021-04-16 23:07 ` [PATCH 2/2] mm: Indicate pfmemalloc pages in compound_head Matthew Wilcox (Oracle)
2021-04-17 21:13 ` David Laight
2021-04-17 21:28 ` Matthew Wilcox
2021-04-20 4:03 ` [PATCH 0/2] Change struct page layout for page_pool Michael Ellerman
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