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

[Hugh Dickins]

On Sun, 12 Feb 2006, Andrew Morton wrote:
> 
> I'm scratching my head over flush_dcache_page() on, say, sparc64.  For
> example, the one in fs/direct-io.c.  With this patch, we'll call
> flush_dcache_page_impl(), which at least won't crash.  Before the patch I
> think we'd just do random stuff.

A head-scratching business indeed.  I think your description is right.

I haven't looked up the intersection of the set of arches which have
hugetlb with the set of arches which do something in flush_dcache_page,
but maybe you have, and found sparc64 the only or most significant.

> But I'm not sure that flush_dcache_page(hugetlb tail page) will do the
> right thing in aither case?

Probably not; but nobody seems to have noticed.  Perhaps it all comes
right in the end somehow.  I haven't much of a clue.

Remember that 1/3 is only changing page[1].mapping i.e. it's making
the first tail page behave like all the other constituents of the
compound page, so it can hardly be making matters worse.

Hugh
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