Re: [PATCH v2] mm/vmscan: add balance_pgdat begin/end tracepoints

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

April 23, 2026 at 8:14 PM, "Bunyod Suvonov" <b.suvonov@sjtu.edu.cn mailto:b.suvonov@sjtu.edu.cn?to=%22Bunyod%20Suvonov%22%20%3Cb.suvonov%40sjtu.edu.cn%3E > 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
> the requested classzone bound (highest_zoneidx). The end tracepoint
> records the node id, the reclaim order that balance_pgdat() finished
> with, the requested classzone bound, and nr_reclaimed. Together, they
> show the requested reclaim order and classzone bound, whether reclaim
> fell back to a lower order, and how much reclaim work was done.
> 
> The end tracepoint also records highest_zoneidx even though it does not
> change within a balance_pgdat() invocation. This keeps the end event
> self-contained, so users can analyze reclaim results directly from end
> events without depending on begin/end correlation, which is less
> convenient when tracing is filtered or records are dropped. It also
> makes it straightforward to relate nr_reclaimed and the final reclaim
> order to the requested classzone bound.
> 
> Signed-off-by: Bunyod Suvonov <b.suvonov@sjtu.edu.cn>

Acked-by: Shakeel Butt <shakeel.butt@linux.dev>