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

[Rik van Riel <riel@redhat.com>]

On 03/10/2011 09:04 PM, Andrea Arcangeli wrote:
> Hello everyone,
>
> 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). I also added native THP support
> without calling split_huge_page unconditionally if both the source and
> destination alignment allows a pmd_trans_huge to be preserved (the
> mremap extension and truncation already preserved existing hugepages
> but the move into new place didn't yet). If the destination alignment
> isn't ok, split_huge_page is unavoidable but that is an
> userland/hardware limitation, not really something we can optimize
> further in the kernel.
>
> I've no real numbers yet (volanomark results are mostly unchanged,
> it's a tinybit faster but it may be measurement error, and it doesn't
> seem to call mremap enough, but the thp_split number in /proc/vmstat
> seem to go down close to zero, maybe other JIT workloads will
> benefit?).

Reviewed-by: Rik van Riel <riel@redhat.com>

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