RE: [PATCH 3/4] mm: move lazy free pages to inactive list

Wang, Yalin
2015-03-11T02:14:59Z

> -----Original Message-----
> From: Minchan Kim [mailto:minchan@kernel.org]
> Sent: Wednesday, March 11, 2015 9:21 AM
> To: Andrew Morton
> Cc: linux-kernel@vger.kernel.org; linux-mm@kvack.org; Michal Hocko;
> Johannes Weiner; Mel Gorman; Rik van Riel; Shaohua Li; Wang, Yalin; Minchan
> Kim
> Subject: [PATCH 3/4] mm: move lazy free pages to inactive list
>
> MADV_FREE is hint that it's okay to discard pages if there is
> memory pressure and we uses reclaimers(ie, kswapd and direct reclaim)
> to free them so there is no worth to remain them in active anonymous LRU
> so this patch moves them to inactive LRU list's head.
>
> This means that MADV_FREE-ed pages which were living on the inactive list
> are reclaimed first because they are more likely to be cold rather than
> recently active pages.
>
> A arguable issue for the approach would be whether we should put it to
> head or tail in inactive list. I selected *head* because kernel cannot
> make sure it's really cold or warm for every MADV_FREE usecase but
> at least we know it's not *hot* so landing of inactive head would be
> comprimise for various usecases.
>
> This is fixing a suboptimal behavior of MADV_FREE when pages living on
> the active list will sit there for a long time even under memory
> pressure while the inactive list is reclaimed heavily. This basically
> breaks the whole purpose of using MADV_FREE to help the system to free
> memory which is might not be used.
>
> Acked-by: Michal Hocko <mhocko@suse.cz>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
> include/linux/swap.h | 1 +
> mm/madvise.c | 2 ++
> mm/swap.c | 35 +++++++++++++++++++++++++++++++++++
> 3 files changed, 38 insertions(+)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index cee108c..0428e4c 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -308,6 +308,7 @@ extern void lru_add_drain_cpu(int cpu);
> extern void lru_add_drain_all(void);
> extern void rotate_reclaimable_page(struct page *page);
> extern void deactivate_file_page(struct page *page);
> +extern void deactivate_page(struct page *page);
> extern void swap_setup(void);
>
> extern void add_page_to_unevictable_list(struct page *page);
> diff --git a/mm/madvise.c b/mm/madvise.c
> index ebe692e..22e8f0c 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -340,6 +340,8 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned
> long addr,
> ptent = pte_mkold(ptent);
> ptent = pte_mkclean(ptent);
> set_pte_at(mm, addr, pte, ptent);
> + if (PageActive(page))
> + deactivate_page(page);
> tlb_remove_tlb_entry(tlb, pte, addr);
> }

I think this place should be changed like this:
+ if (!page_referenced(page, false, NULL, NULL, NULL) && PageActive(page))
+ deactivate_page(page);
Because we don't know if other processes are reference this page,
If it is true, don't need deactivate this page.

Thanks