linux-kernel - RE: [PATCH 1/2] mm: Fix struct page layout on 32-bit systems

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Date:   Sat, 17 Apr 2021 21:18:57 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Matthew Wilcox' <willy@...radead.org>,
        "brouer@...hat.com" <brouer@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        "ilias.apalodimas@...aro.org" <ilias.apalodimas@...aro.org>,
        "mcroce@...ux.microsoft.com" <mcroce@...ux.microsoft.com>,
        "grygorii.strashko@...com" <grygorii.strashko@...com>,
        "arnd@...nel.org" <arnd@...nel.org>, "hch@....de" <hch@....de>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "mhocko@...nel.org" <mhocko@...nel.org>,
        "mgorman@...e.de" <mgorman@...e.de>
Subject: RE: [PATCH 1/2] mm: Fix struct page layout on 32-bit systems

From: Matthew Wilcox <willy@...radead.org>
> Sent: 17 April 2021 03:45
> 
> Replacement patch to fix compiler warning.
...
>  static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
>  {
> -	return page->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;

Ugly as well.

Why not just replace the (dma_addr_t) cast with a (u64) one?
Looks better than the double shift.

Same could be done for the '>> 32'.
Is there an upper_32_bits() that could be used??

	David

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