Re: [PATCH v3 1/3] mm: introduce fincore()

On 07/08/2014 12:03 PM, Naoya Horiguchi wrote:

quoted

quoted

The biggest question for me, though, is whether we want to start
designing these per-page interfaces to consider different page sizes, or
whether we're going to just continue to pretend that the entire world is
4k pages.  Using FINCORE_BMAP on 1GB hugetlbfs files would be a bit
silly, for instance.

I didn't answer this question, sorry.

In my option, hugetlbfs pages should be handled as one hugepage (not as
many 4kB pages) to avoid lots of meaningless data transfer, as you pointed
out. And the current patch already works like that.

Just reading the code, I don't see any way that pc_shift gets passed
down in to the do_fincore() loop.  I don't see it getting reflected in
to 'nr' or 'nr_pages' in there, and I can't see how:

	jump = iter.index - fc->pgstart - nr;

can possibly be right since iter.index is being kept against the offset
in the userspace buffer (4k pages) and 'nr' and fc->pgstart are
essentially done in the huge page size.

If you had a 2-page 1GB-hpage_size() hugetlbfs file, you would only have
two pages in the radix tree, and only two iterations of
radix_tree_for_each_slot().  It would only set the first two bytes of a
256k BMAP buffer since only two pages were encountered in the radix tree.

Or am I reading your code wrong again?

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