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SubjectRe: [PATCH 06/10] mm: vmscan: demote anon DRAM pages to PMEM node
Date
On 22 Mar 2019, at 21:44, Yang Shi wrote:

> Since PMEM provides larger capacity than DRAM and has much lower
> access latency than disk, so it is a good choice to use as a middle
> tier between DRAM and disk in page reclaim path.
>
> With PMEM nodes, the demotion path of anonymous pages could be:
>
> DRAM -> PMEM -> swap device
>
> This patch demotes anonymous pages only for the time being and demote
> THP to PMEM in a whole. However this may cause expensive page reclaim
> and/or compaction on PMEM node if there is memory pressure on it. But,
> considering the capacity of PMEM and allocation only happens on PMEM
> when PMEM is specified explicity, such cases should be not that often.
> So, it sounds worth keeping THP in a whole instead of splitting it.
>
> Demote pages to the cloest non-DRAM node even though the system is
> swapless. The current logic of page reclaim just scan anon LRU when
> swap is on and swappiness is set properly. Demoting to PMEM doesn't
> need care whether swap is available or not. But, reclaiming from PMEM
> still skip anon LRU is swap is not available.
>
> The demotion just happens between DRAM node and its cloest PMEM node.
> Demoting to a remote PMEM node is not allowed for now.
>
> And, define a new migration reason for demotion, called MR_DEMOTE.
> Demote page via async migration to avoid blocking.
>
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
> ---
> include/linux/migrate.h | 1 +
> include/trace/events/migrate.h | 3 +-
> mm/debug.c | 1 +
> mm/internal.h | 22 ++++++++++
> mm/vmscan.c | 99 ++++++++++++++++++++++++++++++++++--------
> 5 files changed, 107 insertions(+), 19 deletions(-)
>
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index e13d9bf..78c8dda 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -25,6 +25,7 @@ enum migrate_reason {
> MR_MEMPOLICY_MBIND,
> MR_NUMA_MISPLACED,
> MR_CONTIG_RANGE,
> + MR_DEMOTE,
> MR_TYPES
> };
>
> diff --git a/include/trace/events/migrate.h b/include/trace/events/migrate.h
> index 705b33d..c1d5b36 100644
> --- a/include/trace/events/migrate.h
> +++ b/include/trace/events/migrate.h
> @@ -20,7 +20,8 @@
> EM( MR_SYSCALL, "syscall_or_cpuset") \
> EM( MR_MEMPOLICY_MBIND, "mempolicy_mbind") \
> EM( MR_NUMA_MISPLACED, "numa_misplaced") \
> - EMe(MR_CONTIG_RANGE, "contig_range")
> + EM( MR_CONTIG_RANGE, "contig_range") \
> + EMe(MR_DEMOTE, "demote")
>
> /*
> * First define the enums in the above macros to be exported to userspace
> diff --git a/mm/debug.c b/mm/debug.c
> index c0b31b6..cc0d7df 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -25,6 +25,7 @@
> "mempolicy_mbind",
> "numa_misplaced",
> "cma",
> + "demote",
> };
>
> const struct trace_print_flags pageflag_names[] = {
> diff --git a/mm/internal.h b/mm/internal.h
> index 46ad0d8..0152300 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -303,6 +303,19 @@ static inline int find_next_best_node(int node, nodemask_t *used_node_mask,
> }
> #endif
>
> +static inline bool has_nonram_online(void)
> +{
> + int i = 0;
> +
> + for_each_online_node(i) {
> + /* Have PMEM node online? */
> + if (!node_isset(i, def_alloc_nodemask))
> + return true;
> + }
> +
> + return false;
> +}
> +
> /* mm/util.c */
> void __vma_link_list(struct mm_struct *mm, struct vm_area_struct *vma,
> struct vm_area_struct *prev, struct rb_node *rb_parent);
> @@ -565,5 +578,14 @@ static inline bool is_migrate_highatomic_page(struct page *page)
> }
>
> void setup_zone_pageset(struct zone *zone);
> +
> +#ifdef CONFIG_NUMA
> extern struct page *alloc_new_node_page(struct page *page, unsigned long node);
> +#else
> +static inline struct page *alloc_new_node_page(struct page *page,
> + unsigned long node)
> +{
> + return NULL;
> +}
> +#endif
> #endif /* __MM_INTERNAL_H */
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index a5ad0b3..bdcab6b 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1094,6 +1094,19 @@ static void page_check_dirty_writeback(struct page *page,
> mapping->a_ops->is_dirty_writeback(page, dirty, writeback);
> }
>
> +static inline bool is_demote_ok(struct pglist_data *pgdat)
> +{
> + /* Current node is not DRAM node */
> + if (!node_isset(pgdat->node_id, def_alloc_nodemask))
> + return false;
> +
> + /* No online PMEM node */
> + if (!has_nonram_online())
> + return false;
> +
> + return true;
> +}
> +
> /*
> * shrink_page_list() returns the number of reclaimed pages
> */
> @@ -1106,6 +1119,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> {
> LIST_HEAD(ret_pages);
> LIST_HEAD(free_pages);
> + LIST_HEAD(demote_pages);
> unsigned nr_reclaimed = 0;
>
> memset(stat, 0, sizeof(*stat));
> @@ -1262,6 +1276,22 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> }
>
> /*
> + * Demote DRAM pages regardless the mempolicy.
> + * Demot anonymous pages only for now and skip MADV_FREE

s/Demot/Demote

> + * pages.
> + */
> + if (PageAnon(page) && !PageSwapCache(page) &&
> + (node_isset(page_to_nid(page), def_alloc_nodemask)) &&
> + PageSwapBacked(page)) {
> +
> + if (has_nonram_online()) {
> + list_add(&page->lru, &demote_pages);
> + unlock_page(page);
> + continue;
> + }
> + }
> +
> + /*
> * Anonymous process memory has backing store?
> * Try to allocate it some swap space here.
> * Lazyfree page could be freed directly
> @@ -1477,6 +1507,25 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page);
> }
>
> + /* Demote pages to PMEM */
> + if (!list_empty(&demote_pages)) {
> + int err, target_nid;
> + nodemask_t used_mask;
> +
> + nodes_clear(used_mask);
> + target_nid = find_next_best_node(pgdat->node_id, &used_mask,
> + true);
> +
> + err = migrate_pages(&demote_pages, alloc_new_node_page, NULL,
> + target_nid, MIGRATE_ASYNC, MR_DEMOTE);
> +
> + if (err) {
> + putback_movable_pages(&demote_pages);
> +
> + list_splice(&ret_pages, &demote_pages);
> + }
> + }
> +

I like your approach here. It reuses the existing migrate_pages() interface without
adding extra code. I also would like to be CC’d in your future versions.

Thank you.

--
Best Regards,
Yan Zi
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