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SubjectRe: [patch 7/7] mm: reduce rmap overhead for ex-KSM page copies created on swap faults
On Mon, 17 Dec 2012, Johannes Weiner wrote:

> When ex-KSM pages are faulted from swap cache, the fault handler is
> not capable of re-establishing anon_vma-spanning KSM pages. In this
> case, a copy of the page is created instead, just like during a COW
> break.
>
> These freshly made copies are known to be exclusive to the faulting
> VMA and there is no reason to go look for this page in parent and
> sibling processes during rmap operations.
>
> Use page_add_new_anon_rmap() for these copies. This also puts them on
> the proper LRU lists and marks them SwapBacked, so we can get rid of
> doing this ad-hoc in the KSM copy code.
>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> Reviewed-by: Rik van Riel <riel@redhat.com>

Yes, that's good, thanks Hannes:
Acked-by: Hugh Dickins <hughd@google.com>

> ---
> mm/ksm.c | 6 ------
> mm/memory.c | 5 ++++-
> 2 files changed, 4 insertions(+), 7 deletions(-)
>
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 382d930..7275c74 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -1590,13 +1590,7 @@ struct page *ksm_does_need_to_copy(struct page *page,
>
> SetPageDirty(new_page);
> __SetPageUptodate(new_page);
> - SetPageSwapBacked(new_page);
> __set_page_locked(new_page);
> -
> - if (!mlocked_vma_newpage(vma, new_page))
> - lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
> - else
> - add_page_to_unevictable_list(new_page);
> }
>
> return new_page;
> diff --git a/mm/memory.c b/mm/memory.c
> index db2e9e7..7e17eb0 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3020,7 +3020,10 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
> }
> flush_icache_page(vma, page);
> set_pte_at(mm, address, page_table, pte);
> - do_page_add_anon_rmap(page, vma, address, exclusive);
> + if (swapcache) /* ksm created a completely new copy */
> + page_add_new_anon_rmap(page, vma, address);
> + else
> + do_page_add_anon_rmap(page, vma, address, exclusive);
> /* It's better to call commit-charge after rmap is established */
> mem_cgroup_commit_charge_swapin(page, ptr);
>
> --
> 1.7.11.7


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