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

To: Matthew Wilcox <willy@linux.intel.com>
Subject: Re: [PATCH] remap_file_pages needs to check for cache coherency
From: John David Anglin <dave.anglin@bell.net>
Date: Fri, 27 Dec 2013 14:13:16 -0500
Cc: linux-mm@kvack.org, "David S. Miller" <davem@davemloft.net>, sparclinux@vger.kernel.org, linux-parisc@vger.kernel.org, linux-mips@linux-mips.org
In-reply-to: <20131227180018.GC4945@linux.intel.com>
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On 27-Dec-13, at 1:00 PM, Matthew Wilcox wrote:

+#ifdef __ARCH_FORCE_SHMLBA
+       /* Is the mapping cache-coherent? */
+       if ((pgoff ^ linear_page_index(vma, start)) &
+           ((SHMLBA-1) >> PAGE_SHIFT))
+               goto out;
+#endif


I think this will cause problems on PA-RISC. The reason is we have an additional offset
for mappings.  See get_offset() in sys_parisc.c.

SHMLBA is 4 MB on PA-RISC. If we limit ourselves to aligned mappings, we run out of memory very quickly. Even with our current implementation, we fail the perl locales test
with locales-all installed.

Dave
--
John David Anglin       dave.anglin@bell.net




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