Re: [PATCH] vmscan: add a vmscan event for reclaim_pages
From: Vlastimil Babka
Date: Fri Oct 11 2024 - 04:53:14 EST
On 10/11/24 10:25 AM, Jaewon Kim wrote:
> Hi
>
> Thank you for your coment. Yes if it is allowed, I can do that way. When
> I checked, the following functions should do the memset().
>
> reclaim_clean_pages_from_list
> shrink_inactive_list
> reclaim_folio_list
> evict_folios
>
> Actually I was planning to move trace_mm_vmscan_reclaim_pages into
> reclaim_folio_list so that we don't have to sum up and we may be able
> to print node number, too. As we will see log for each node, if we'd
> like to know the sum, that would be the post parser's job.
>
> Option 1. No change on memset, but print on each node.
> mm_vmscan_reclaim_pages: nid=0 nr_scanned=112 nr_reclaimed=112 nr_dirty=0 nr_writeback=0 nr_congested=0 nr_immediate=0 nr_activate_anon=0 nr_activate_file=0 nr_ref_keep=0 nr_unmap_fail=0
> mm_vmscan_reclaim_pages: nid=1 ...
> mm_vmscan_reclaim_pages: nid=2 ...
I see. Note it processes a list that might be from multiple nodes and
will group consecutive pages from the same node, but if pages come from
random nodes, the nodes will repeat and there might be many trace
events, each for few pages only.
Guess it depends on the workload if it has its pages from the same node.
Maybe you can try and see how noisy it is in practice?
> Option 2. Change on memset, but we don't care the stat from each node.
> mm_vmscan_reclaim_pages: nr_scanned=35 nr_reclaimed=35 nr_dirty=0 nr_writeback=0 nr_congested=0 nr_immediate=0 nr_activate_anon=0 nr_activate_file=0 nr_ref_keep=0 nr_unmap_fail=0
>
> Would you give me you preference between the two options?
>
> Thank you
> Jaewon Kim
>
>>
>> AFAICS shrink_folio_list() only cares about these fields:
>>
>> pgactivate = stat->nr_activate[0] + stat->nr_activate[1];
>>
>> in order to do
>>
>> count_vm_events(PGACTIVATE, pgactivate);
>>
>> Which could be adjusted to deal with accumulating stat - i.e. take an
>> initial sum of the fields in stat and subtract from the final sum to get
>> the delta.
>>
>>> unsigned long reclaim_pages(struct list_head *folio_list)
>>> {
>>> int nid;
>>> + unsigned int nr_scanned = 0;
>>> unsigned int nr_reclaimed = 0;
>>> LIST_HEAD(node_folio_list);
>>> unsigned int noreclaim_flag;
>>> + struct reclaim_stat stat_total, stat_one;
>>>
>>> if (list_empty(folio_list))
>>> return nr_reclaimed;
>>>
>>> + memset(&stat_total, 0, sizeof(stat_total));
>>> noreclaim_flag = memalloc_noreclaim_save();
>>>
>>> nid = folio_nid(lru_to_folio(folio_list));
>>> @@ -2168,14 +2192,20 @@ unsigned long reclaim_pages(struct list_head *folio_list)
>>> if (nid == folio_nid(folio)) {
>>> folio_clear_active(folio);
>>> list_move(&folio->lru, &node_folio_list);
>>> + nr_scanned += folio_nr_pages(folio);
>>> continue;
>>> }
>>>
>>> - nr_reclaimed += reclaim_folio_list(&node_folio_list, NODE_DATA(nid));
>>> + nr_reclaimed += reclaim_folio_list(&node_folio_list,
>>> + NODE_DATA(nid), &stat_one);
>>> + reclaim_stat_add(&stat_one, &stat_total);
>>> nid = folio_nid(lru_to_folio(folio_list));
>>> } while (!list_empty(folio_list));
>>>
>>> - nr_reclaimed += reclaim_folio_list(&node_folio_list, NODE_DATA(nid));
>>> + nr_reclaimed += reclaim_folio_list(&node_folio_list, NODE_DATA(nid),
>>> + &stat_one);
>>> + reclaim_stat_add(&stat_one, &stat_total);
>>> + trace_mm_vmscan_reclaim_pages(nr_scanned, nr_reclaimed, &stat_total);
>>>
>>> memalloc_noreclaim_restore(noreclaim_flag);
>>>