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Re: [PATCH] remap_file_pages needs to check for cache coherency

To: Matthew Wilcox <>
Subject: Re: [PATCH] remap_file_pages needs to check for cache coherency
From: John David Anglin <>
Date: Fri, 27 Dec 2013 14:47:32 -0500
Cc:, "David S. Miller" <>,,,
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On 27-Dec-13, at 2:33 PM, Matthew Wilcox wrote:

Have you considered measuring SHMLBA on different CPU models and
reducing it at boot time? I know that 4MB is the architectural guarantee (actually, I seem to remember that 16MB was the architectural guarantee,
but jsm found some CPU architects who said it would enver exceed 4MB).
I bet some CPUs have considerably lower cache coherency limits.

It's worth looking at. The value is supposed to be returned by the PDC_CACHE PDC call but I know my rp3440 returns a value of 0 indicating that the aliasing boundary
is unknown and may be greater than 16MB.

John David Anglin

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