Re: [PATCH 06/10] mm: vmscan: demote anon DRAM pages to PMEM node

Yang Shi
2019-03-25T21:49:54Z

On 3/22/19 11:03 PM, Zi Yan wrote:
> 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

Thanks for catching this. Will fix.

>
>> + * 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.

Yes, sure.

Thanks,
Yang

>
> Thank you.
>
> --
> Best Regards,
> Yan Zi