kernel/linux.git/include/trace/events/memcg.h, branch v7.1

mm: memcontrol: change val type to long in __mod_memcg_{lruvec_}state()

2026-04-18T07:10:48+00:00

The __mod_memcg_state() and __mod_memcg_lruvec_state() functions are also used to reparent non-hierarchical stats. In this scenario, the values passed to them are accumulated statistics that might be extremely large and exceed the upper limit of a 32-bit integer. Change the val parameter type from int to long in these functions and their corresponding tracepoints (memcg_rstat_stats) to prevent potential overflow issues. After that, in memcg_state_val_in_pages(), if the passed val is negative, the expression val * unit / PAGE_SIZE could be implicitly converted to a massive positive number when compared with 1UL in the max() macro. This leads to returning an incorrect massive positive value. Fix this by using abs(val) to calculate the magnitude first, and then restoring the sign of the value before returning the result. Additionally, use mult_frac() to prevent potential overflow during the multiplication of val and unit. Link: https://lore.kernel.org/70a9440e49c464b4dca88bcabc6b491bd335c9f0.1774604356.git.zhengqi.arch@bytedance.com Signed-off-by: Qi Zheng Reported-by: Harry Yoo (Oracle) Reviewed-by: Lorenzo Stoakes (Oracle) Reviewed-by: Harry Yoo (Oracle) Cc: Allen Pais Cc: Axel Rasmussen Cc: Baoquan He Cc: David Hildenbrand Cc: Hamza Mahfooz Cc: Hugh Dickins Cc: Imran Khan Cc: Johannes Weiner Cc: Kamalesh Babulal Cc: Lance Yang Cc: Michal Hocko Cc: Michal Koutný Cc: Muchun Song Cc: Roman Gushchin Cc: Shakeel Butt Cc: Usama Arif Cc: Wei Xu Cc: Yuanchu Xie Cc: Zi Yan Signed-off-by: Andrew Morton

memcg: add flush tracepoint

2024-11-11T08:26:46+00:00

This tracepoint gives visibility on how often the flushing of memcg stats occurs and contains info on whether it was forced, skipped, and the value of stats updated. It can help with understanding how readers are affected by having to perform the flush, and the effectiveness of the flush by inspecting the number of stats updated. Paired with the recently added tracepoints for tracing rstat updates, it can also help show correlation where stats exceed thresholds frequently. Link: https://lkml.kernel.org/r/20241029021106.25587-3-inwardvessel@gmail.com Signed-off-by: JP Kobryn Reviewed-by: Yosry Ahmed Acked-by: Shakeel Butt Cc: Johannes Weiner Cc: Steven Rostedt (Google) Signed-off-by: Andrew Morton

memcg: add tracing for memcg stat updates

2024-11-07T04:11:12+00:00

The memcg stats are maintained in rstat infrastructure which provides very fast updates side and reasonable read side. However memcg added plethora of stats and made the read side, which is cgroup rstat flush, very slow. To solve that, threshold was added in the memcg stats read side i.e. no need to flush the stats if updates are within the threshold. This threshold based improvement worked for sometime but more stats were added to memcg and also the read codepath was getting triggered in the performance sensitive paths which made threshold based ratelimiting ineffective. We need more visibility into the hot and cold stats i.e. stats with a lot of updates. Let's add trace to get that visibility. [shakeel.butt@linux.dev: use unsigned long type for memcg_rstat_events, per Yosry] Link: https://lkml.kernel.org/r/20241015213721.3804209-1-shakeel.butt@linux.dev Link: https://lkml.kernel.org/r/20241010003550.3695245-1-shakeel.butt@linux.dev Signed-off-by: Shakeel Butt Acked-by: Roman Gushchin Reviewed-by: Yosry Ahmed Acked-by: Johannes Weiner Reviewed-by: T.J. Mercier Cc: Michal Hocko Cc: Muchun Song Cc: JP Kobryn Cc: Steven Rostedt (Google) Signed-off-by: Andrew Morton