On Fri, 18 Jan 2008, Anton Salikhmetov wrote:
>
> The current solution doesn't hit the performance at all when compared to
> the competitor POSIX-compliant systems. It is faster and does even more
> than the POSIX standard requires.
Your current patches have two problems:
- they are simply unnecessarily invasive for a relatively simple issue
- all versions I've looked at closer are buggy too
Example:
+ if (pte_dirty(*pte) && pte_write(*pte))
+ *pte = pte_wrprotect(*pte);
Uhhuh. Looks simple enough. Except it does a non-atomic pte access while
other CPU's may be accessing it and updating it from their hw page table
walkers. What will happen? Who knows? I can see lost access bits at a
minimum.
IOW, this isn't simple code. It's code that it is simple to screw up. In
this case, you really need to use ptep_set_wrprotect(), for example.
So why not do it in many fewer lines with that simpler vma->dirty flag?
Linus
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