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Date: Sat, 20 Jun 2009 22:27:20 +0200 From: Ingo Molnar <mingo@...e.hu> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: linux-kernel@...r.kernel.org, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Thomas Gleixner <tglx@...utronix.de>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [GIT PULL] core kernel fixes * Linus Torvalds <torvalds@...ux-foundation.org> wrote: > On Sat, 20 Jun 2009, Linus Torvalds wrote: > > > > On x86, the natural way to do what you want done is ONE SINGLE > > INSTRUCTION! As far as I can tell, the above crazy function is 100% > > equivalent to this: > > > > asm __inline__("lock ; addl $0,%0":"+m" (*uaddr): :"memory", "cc"); > > > > which really makes me think that using "get_user_pages_fast()" for it is > > some truly crazy crap. > > We could also take the opposite approach - knowing that this is called > only when the page doesn't exist, and just doing > > down_read(mmap_sem) > vma = find_vma(..) > ret = VM_FAULT_ERROR; > if (vma && vma->vm_start <= address) > ret = handle_mm_fault(mm, vma, address, 1); > up_read(mmap_sem); > return (ret & VM_FAULT_ERROR) ? -EFAULT : 0; > > or something like that. Again, that looks saner than using > get_user_pages() for this and then dropping the page. We'll sort this out tomorrow, sorry about this. ( The other embarrasing bit is that i flagged this commit as bad nine days ago - during review i noticed the same bad pattern of a pointless get-put cycle ... but the commit stuck around and forgot about it. Sloppy. ) Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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