Re: [PATCH] mm/vmscan: add balance_pgdat begin/end tracepoints

[Shakeel Butt <shakeel.butt@linux.dev>]

On Thu, Apr 23, 2026 at 06:37:53PM +0800, Bunyod Suvonov wrote:
> Vmscan has six main reclaim entry points: try_to_free_pages() for
> direct reclaim, try_to_free_mem_cgroup_pages() for memcg reclaim,
> mem_cgroup_shrink_node() for memcg soft limit reclaim, node_reclaim()
> for node reclaim, shrink_all_memory() for hibernation reclaim, and
> balance_pgdat() for kswapd reclaim.
> 
> All of them, except for shrink_all_memory() and balance_pgdat(), already
> have begin/end tracepoints. This makes it harder to trace which reclaim
> path is responsible for memory reclaim activity, because kswapd reclaim
> cannot be identified as cleanly as other reclaim entry points, even
> though it is the main background reclaim path under memory pressure.
> There may be no need to trace shrink_all_memory() as it is primarily
> used during hibernation. So this patch adds the missing tracepoint pair
> for balance_pgdat().
> 
> The begin tracepoint records the node id, requested reclaim order, and
> highest_zoneidx. The end tracepoint records the node id, reclaim order
> that balance_pgdat() finished with, highest_zoneidx, and nr_reclaimed.

Do we need to trace highest_zoneidx at the end? Can it change within
balance_pgdat()?

> Together, they show the requested reclaim order and zone bound, whether
> reclaim fell back to a lower order, and how much reclaim work was done.
> 
> Signed-off-by: Bunyod Suvonov <b.suvonov@sjtu.edu.cn>

Overall looks good.