Re: [PATCH] thp: mremap support and TLB optimization

[Hugh Dickins <hughd@google.com>]

On Thu, Mar 10, 2011 at 6:04 PM, Andrea Arcangeli <aarcange@redhat.com> wrote:
>
> I've been wondering why mremap is sending one IPI for each page that
> it moves. I tried to remove that so we send an IPI for each
> vma/syscall (not for each pte/page).

(It wouldn't usually have been sending an IPI for each page, only if
the mm were active on another cpu, but...)

That looks like a good optimization to me: I can't think of a good
reason for it to be the way it was, just it started out like that and
none of us ever thought to change it before.  Plus it's always nice to
see the flush_tlb_range() afterwards complementing the
flush_cache_range() beforehand, as you now have in move_page_tables().

And don't forget that move_page_tables() is also used by exec's
shift_arg_pages(): no IPI saving there, but it should be more
efficient when exec'ing with many arguments.

Hugh

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