On 2025/5/23 13:25, Donet Tom wrote:
On 5/23/25 8:46 AM, Baolin Wang wrote:
On some large machines with a high number of CPUs running a 64K kernel,
we found that the 'RES' field is always 0 displayed by the top command
for some processes, which will cause a lot of confusion for users.
PID USER PR NI VIRT RES SHR S %CPU %MEM
TIME+ COMMAND
875525 root 20 0 12480 0 0 R 0.3 0.0
0:00.08 top
1 root 20 0 172800 0 0 S 0.0 0.0
0:04.52 systemd
The main reason is that the batch size of the percpu counter is quite
large
on these machines, caching a significant percpu value, since
converting mm's
rss stats into percpu_counter by commit f1a7941243c1 ("mm: convert
mm's rss
stats into percpu_counter"). Intuitively, the batch number should be
optimized,
but on some paths, performance may take precedence over statistical
accuracy.
Therefore, introducing a new interface to add the percpu statistical
count
and display it to users, which can remove the confusion. In addition,
this
change is not expected to be on a performance-critical path, so the
modification
should be acceptable.
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
fs/proc/task_mmu.c | 14 +++++++-------
include/linux/mm.h | 5 +++++
2 files changed, 12 insertions(+), 7 deletions(-)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index b9e4fbbdf6e6..f629e6526935 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -36,9 +36,9 @@ void task_mem(struct seq_file *m, struct mm_struct *mm)
unsigned long text, lib, swap, anon, file, shmem;
unsigned long hiwater_vm, total_vm, hiwater_rss, total_rss;
- anon = get_mm_counter(mm, MM_ANONPAGES);
- file = get_mm_counter(mm, MM_FILEPAGES);
- shmem = get_mm_counter(mm, MM_SHMEMPAGES);
+ anon = get_mm_counter_sum(mm, MM_ANONPAGES);
Hi Baolin Wang,
We also observed the same issue where the RSS value in /proc/PID/status
was 0 on machines with a high number of CPUs. With this patch, the issue
got fixedl
Yes, we also observed this issue.
Rss value without this patch
----------------------------
# cat /proc/87406/status
.....
VmRSS: 0 kB
RssAnon: 0 kB
RssFile: 0 k
Rss values with this patch
--------------------------
# cat /proc/3055/status
VmRSS: 2176 kB
RssAnon: 512 kB
RssFile: 1664 kB
RssShmem: 0 kB
Tested-by Donet Tom <donettom@xxxxxxxxxxxxx>
Thanks for testing.
