Re: [PATCH] vmscan: add a vmscan event for reclaim_pages

[Andrew Morton]

On Wed,  9 Oct 2024 18:31:24 +0900 Jaewon Kim <jaewon31.kim@xxxxxxxxxxx> wrote:

> The reclaim_folio_list uses a dummy reclaim_stat and is not being
> used. To know the memory stat, add a new trace event. This is useful how
> how many pages are not reclaimed or why.
> 
> This is an example.
> mm_vmscan_reclaim_pages: nr_scanned=17 nr_reclaimed=17 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
> 
> Currenlty reclaim_folio_list is only called by reclaim_pages, and
> reclaim_pages is used by damon and madvise. In the latest Android,
> reclaim_pages is also used by shmem to reclaim all pages in a
> address_space.
> 

This looks like it will add some overhead when tracing has been
enabled.  Has this been measured and is it significant?

Also, we're adding a significant amount of code for a simple trace
record.  Do others think this is justifiable?