linux-kernel - Re: [PATCH 1/2] Introduce copy_user_handle

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Date:	Mon, 07 Jul 2008 14:09:10 +0200
From:	Vitaly Mayatskikh <v.mayatskih@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Vitaly Mayatskikh <v.mayatskih@...il.com>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] Introduce copy_user_handle_tail routine

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> Now, the stuff that comes *before* that point is the "try to fix up one 
> byte at a time" thing, which I'd like to be simple and dumb. At least to 
> start with.

Just to be clear: do these patches are good enough now (to start with)?
Or, may be, it needs to be further improved?

> Of course, I also suspect that *eventually* we might want to make it 
> smarter and more complex. For example, while performance isn't a primary 
> issue, we might want to eventually avoid having to do _two_ faults (once 
> in the fast unrolled or word-at-a-time loop, and once in the byte-for-byte 
> one), by limiting the byte-for-byte one to be within a page, but that 
> would be a "future enhancement" thing.

Btw, how much does it cost to CPU to do a fault? Can it be compared with
average time of find_vma()?

-- 
wbr, Vitaly
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