Date: Sun, 23 Feb 2003 09:49:58 +0000 From: Christoph Hellwig <hch@infradead.org> To: Terry Lambert <tlambert2@mindspring.com> Cc: Byunghyun Oh <octphial@postech.ac.kr>, freebsd-hackers@freebsd.org Subject: Re: Replacement for get_user_pages() of Linux Message-ID: <20030223094958.A15347@infradead.org> In-Reply-To: <3E588B1B.484C4D61@mindspring.com>; from tlambert2@mindspring.com on Sun, Feb 23, 2003 at 12:49:31AM -0800 References: <20030223163746.A19421@shell.postech.ac.kr> <3E588B1B.484C4D61@mindspring.com>
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On Sun, Feb 23, 2003 at 12:49:31AM -0800, Terry Lambert wrote: > I've been unable to find any documentation on get_user_pages(), > and you didn't provide a link to any. > > But looking at the source code, the reason for doing this is to > permit DMA directly into user pages. > > I don't understand what you mean by "pin", in this context. get_user_pages() does the following: (1) force all pages into physical memory if they weren't before (2) increment the usage count on the to avoid paging them out The latter is usually called page pinning. > You are aware that FreeBSD has a unified VM and buffer cache, and > all user pages for the current process are automatically visible > in th kernel address space, with no need to call something like > get_user_pages() to establish a mapping, right? get_user_pages() does not establish a mapping, in Linux you don't need a kernel mapping to perform DMA on memory. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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