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Date: Mon, 7 Nov 2011 09:08:03 -0800 From: Dave Hylands <dhylands@...il.com> To: loody <miloody@...il.com> Cc: Jonathan Corbet <corbet@....net>, LKML <linux-kernel@...r.kernel.org>, kernelnewbies@...nelnewbies.org Subject: Re: some questions about block and scatterlist Hi loody, On Mon, Nov 7, 2011 at 5:16 AM, loody <miloody@...il.com> wrote: ...snip... >>> 1. Are all struct page 32-bit aligned? >> >> Certainly, I would expect any structures found in the system memory map to >> be so aligned, yes. If you've created an arbitrary one elsewhere I'm only >> 99% sure it would be. >> >>> If so, where is this part of code for handleing struct page be 32-bits aligned? >> >> Note that the size of struct page is carefully considered, and that they >> are packed as densely as possible, both externally and internally. No >> lesser alignment would make sense. > I found kernel stealing LSB of page_link to put additional > information, such as sg_is_chain and sg_is_last. > > That means the address of all pages have to be at least 4byte alignment. > But I didn't see any additional attribute added at the end of struct > or any precaution to take care this. This is done automatically by the compiler. http://en.wikipedia.org/wiki/Data_structure_alignment -- Dave Hylands Shuswap, BC, Canada http://www.davehylands.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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