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Re: [libc/string] State of PAGE_COPY_FWD / PAGE_COPY_THRESHOLD

From: Florian Weimer <fweimer at redhat dot com>
To: Maxim Kuvyrkov <maxim dot kuvyrkov at linaro dot org>, GNU C Library <libc-alpha at sourceware dot org>
Date: Thu, 10 Nov 2016 09:27:39 +0100
Subject: Re: [libc/string] State of PAGE_COPY_FWD / PAGE_COPY_THRESHOLD
Authentication-results: sourceware.org; auth=none
References: <E122D105-776D-4B9B-A15C-0A7C24BC0910@linaro.org>

On 11/01/2016 10:28 AM, Maxim Kuvyrkov wrote:

I wanted to check performance impact of using linux zero page sharing in calls to memset (PTR, 0, SIZE).  I remembered seeing PAGE_COPY_FWD_MAYBE and PAGE_COPY_THRESHOLD in string/memcpy.c, and my plan was to copy this logic to an experimental memset() implementation.

Closer inspection of the current code showed that only Mach port attempted to use full-page copying in memcpy.c, but now even the Mach port disables it.  The net result is that code in string/memcpy.c, as well as parts of headers sysdeps/generic/pagecopy.h and sysdeps/generic/memcopy.h are dead code.


I posted a patch to remove this, but it got stalled.

The Mach port no longer compiles on the master branch, so I don't knowhow we can make changes to it.


Florian

References:
- [libc/string] State of PAGE_COPY_FWD / PAGE_COPY_THRESHOLD
  - From: Maxim Kuvyrkov

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