Re: [PATCH 22 of 31] split_huge_page paging

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

On 01/26/2010 08:52 AM, Andrea Arcangeli wrote:
> From: Andrea Arcangeli<aarcange@redhat.com>
>
> Paging logic that splits the page before it is unmapped and added to swap to
> ensure backwards compatibility with the legacy swap code. Eventually swap
> should natively pageout the hugepages to increase performance and decrease
> seeking and fragmentation of swap space. swapoff can just skip over huge pmd as
> they cannot be part of swap yet. In add_to_swap be careful to split the page
> only if we got a valid swap entry so we don't split hugepages with a full swap.
>
> Signed-off-by: Andrea Arcangeli<aarcange@redhat.com>
> ---
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -378,6 +378,8 @@ static void collect_procs_anon(struct pa
>   	struct task_struct *tsk;
>   	struct anon_vma *av;
>
> +	if (unlikely(split_huge_page(page)))
> +		return;
>   	read_lock(&tasklist_lock);
>   	av = page_lock_anon_vma(page);
>   	if (av == NULL)	/* Not actually mapped anymore */
> diff --git a/mm/rmap.c b/mm/rmap.c
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1174,6 +1174,7 @@ int try_to_unmap(struct page *page, enum
>   	int ret;
>
>   	BUG_ON(!PageLocked(page));
> +	BUG_ON(PageTransHuge(page));
>
>   	if (unlikely(PageKsm(page)))
>   		ret = try_to_unmap_ksm(page, flags);
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -156,6 +156,12 @@ int add_to_swap(struct page *page)
>   	if (!entry.val)
>   		return 0;
>
> +	if (unlikely(PageTransHuge(page)))
> +		if (unlikely(split_huge_page(page))) {
> +			swapcache_free(entry, NULL);
> +			return 0;
> +		}
> +
>   	/*
>   	 * Radix-tree node allocations from PF_MEMALLOC contexts could
>   	 * completely exhaust the page allocator. __GFP_NOMEMALLOC

Shouldn't we split up these pages in vmscan.c, before calling
add_to_swap() ?

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