Re: Assumed Failure rates in Various o.s's ?

["Benjamin C.R. LaHaise" <blah@kvack.org>]

On Fri, 21 May 1999, Erik Corry wrote:

> According to Andi you already fixed this with a read lock that
> prevents mmap and mmunmap from doing anything while the copy
> is running.  This makes sense, since if you do it right with a
> readers/writers lock you can keep out mmap without serialising
> copy_to_user or copy_from_user.

I really like the cleanliness of this approach, but it's troublesome:
memory allocations in other threads would then get blocked during large
IOs -- very bad.  What if we instead move from the mm level semaphore to a
per vma locking scheme?  The mmap semaphore could become a spinlock for
fudging with list of vmas, and mmap/page faults/... could lock the
specific vma.  Or would this be too heavy?

		-ben

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