Re: [uml-user] Re: [uml-devel] Dynamic remount with variable COW stacking/merging needed, support for snapshot repilication

[Jeff Dike <jdike@addtoit.com>]

adam@doogie.org said:
> The problem is that you can't request multiple pages at once with
> mmap.  Only one page at a time(because the page you requested will
> fault, which will pause the process while the system pages it in). 

No, mmap itself doesn't fault.  It fiddles some data structures and returns
immediately.  The fault happens when the page is first touched.  That's why
the ubd IO thread touches the page after a request is satified my mmap - to
fault the page in in an asynchronous way.

I would love for there to be aio page fault notification.

> In fact, mmap can be slower in some cases than normal reading, if the
> kernel only pages in one block at a time(because of other reasons). 

In a lot of cases, actually.  The tlb operations associated with changing
mappings are expensive, and can outweigh a lot of copying.

				Jeff



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