From: Matthew Wilcox <willy@infradead.org>
To: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: arnd@kernel.org, grygorii.strashko@ti.com,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mips@vger.kernel.org, mhocko@kernel.org,
linux-mm@kvack.org, mgorman@suse.de, brouer@redhat.com,
mcroce@linux.microsoft.com, linux-snps-arc@lists.infradead.org,
linuxppc-dev@lists.ozlabs.org, hch@lst.de,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/2] mm: Fix struct page layout on 32-bit systems
Date: Sat, 17 Apr 2021 21:22:40 +0100 [thread overview]
Message-ID: <20210417202240.GS2531743@casper.infradead.org> (raw)
In-Reply-To: <YHspptFx+T588KcG@apalos.home>
On Sat, Apr 17, 2021 at 09:32:06PM +0300, Ilias Apalodimas wrote:
> > +static inline void page_pool_set_dma_addr(struct page *page, dma_addr_t addr)
> > +{
> > + page->dma_addr[0] = addr;
> > + if (sizeof(dma_addr_t) > sizeof(unsigned long))
> > + page->dma_addr[1] = addr >> 16 >> 16;
>
> The 'error' that was reported will never trigger right?
> I assume this was compiled with dma_addr_t as 32bits (so it triggered the
> compilation error), but the if check will never allow this codepath to run.
> If so can we add a comment explaining this, since none of us will remember why
> in 6 months from now?
That's right. I compiled it all three ways -- 32-bit, 64-bit dma, 32-bit long
and 64-bit. The 32/64 bit case turn into:
if (0)
page->dma_addr[1] = addr >> 16 >> 16;
which gets elided. So the only case that has to work is 64-bit dma and
32-bit long.
I can replace this with upper_32_bits().
next prev parent reply other threads:[~2021-04-17 20:23 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 [this message]
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
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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