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Date:	Thu, 16 Sep 2010 08:48:25 +0200 (CEST)
From:	"Andi Kleen" <>
Cc:	"Andi Kleen" <>,
	"Andrew Morton" <>,
	"Ingo Molnar" <>, "Theodore Ts'o" <>,
	"Chris Mason" <>,
	"Linux Kernel" <>,
	"Linux Btrfs" <>,
	"Linux Ext4" <>
Subject: Re: [PATCH] x86_64/lib: improve the performance of memmove

> When the dest and the src do overlap and the memory area is large, memmove
> of
> x86_64 is very inefficient, and it led to bad performance, such as btrfs's
> file
> deletion performance. This patch improved the performance of memmove on
> x86_64
> by using __memcpy_bwd() instead of byte copy when doing large memory area
> copy
> (len > 64).

I still don't understand why you don't simply use a backwards
string copy (with std) ? That should be much simpler and
hopefully be as optimized for kernel copies on recent CPUs.


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