Re: [PATCH 1/3] compound page: use page[1].lru

[David S. Miller]

From: Andrew Morton <akpm@xxxxxxxx>
Date: Sun, 12 Feb 2006 18:13:12 -0800

> We have a page which has no ->mapping, but lo, it's mmapped by userspace
> and can be MAP_SHARED between different CPUs and processes.
> 
> Yes, I suspect it'll do the wrong thing in unpleasantly subtle ways.
> 
> (cc's davem and runs away).

The ->mapping check is there essentially to hit user mapped pages that
would be modified by the kernel using kernel space memory accesses
other than those done by copy_user_page() and clear_user_page() (and
their brothers copy_user_highpage() and clear_user_highpage() which
just call the former directly on a non-HIGHPAGE platform like
sparc64).

Hugepages actually have no D-cache aliasing issues by definition on
sparc64 because the smallest possible hugepage size is 64K which is
larger than the D-cache aliasing factor (which is 16K).
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