Date: Mon, 2 Mar 2015 16:12:27 -0800 From: "K. Macy" <kmacy@freebsd.org> To: Adrian Chadd <adrian@freebsd.org> Cc: freebsd-current <freebsd-current@freebsd.org>, "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org> Subject: Re: Doing zero-copy stuff in drivers, or "is vm_fault_quick_hold_pages() enough" ? Message-ID: <CAHM0Q_PsTVZgfwnY7MuE7cBxchcufpACDu2wjUc_Yvuv858Yxw@mail.gmail.com> In-Reply-To: <CAJ-VmonpLG4BTmJvnzOe7HJMaZ3Z8iVzwG62xZkAtCHb=94AQA@mail.gmail.com> References: <CAJ-Vmom87%2BC0dT5gj8YVGH-QjqDHU3otKeb9XaDSnwwzrY5hPQ@mail.gmail.com> <CAHM0Q_PnW%2BmhSU4SeAuwBJvvAx6G3fsVDNAN6Fpt1JUFn5_ysQ@mail.gmail.com> <CAJ-VmonpLG4BTmJvnzOe7HJMaZ3Z8iVzwG62xZkAtCHb=94AQA@mail.gmail.com>
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>> Right above vm_page_hold():
>> /*
>> * Keep page from being freed by the page daemon
>> * much of the same effect as wiring, except much lower
>> * overhead and should be used only for *very* temporary
>> * holding ("wiring").
>> */
>
> What's the definition of "very temporary holding" ? What's the
> behavioural difference?
Long enough to complete a DMA operation versus the lifetime of an
executing program.
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