Re: [RFC][PATCH] page->mapping clarification [1/3] base functions

From: Hugh Dickins
Date: Wed Sep 26 2007 - 15:31:50 EST

On Sat, 22 Sep 2007, KAMEZAWA Hiroyuki wrote:
> On Fri, 21 Sep 2007 18:02:47 +0100 (BST)
> Hugh Dickins <hugh@xxxxxxxxxxx> wrote:
> > Or should I now leave PG_swapcache as is,
> > given your designs on page->mapping?
> >
> will conflict with my idea ?
> ==
> ==

I asked because I had thought it would be a serious conflict: obviously
the patches as such would conflict quite a bit, but that's not serious,
one or the other just gets fixed up.

But now I don't see it - we both want to grab a further bit from the
low bits of the page->mapping pointer, you PAGE_MAPPING_INFO and me
PAGE_MAPPING_SWAP; but that's okay, so long as whoever is left using
bit (1<<2) is careful about the 32-bit case and remembers to put
__attribute__((aligned(sizeof(long long))))
on the declarations of struct address_space and struct anon_vma
and your struct page_mapping_info.

Would that waste a little memory? I think not with SLUB,
but perhaps with SLOB, which packs a little tighter.

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