Re:[PATCH] alloc_tag: avoid mem alloc and iter reset when reading allocinfo

David Wang
2025-05-07T18:19:48Z

Hi,
Just want to share how I notice those memory allocation behaivors: the cumulative counters~!

With cumulative counters, I can identify which module keeps alloc/free memory, by the ratio between
cumulative calls and remaining calls, and maybe an optimization could be applied.
Following is top16 I got on my system:

+-----------------------------------------+-------+------------------+--------------------+
| alloc | calls | cumulative calls | ratio |
+-----------------------------------------+-------+------------------+--------------------+
| fs/seq_file.c:584 | 2 | 18064825 | 9032412.5 |
| fs/seq_file.c:38 | 5 | 18148288 | 3629657.6 |
| fs/seq_file.c:63 | 15 | 18153271 | 1210218.0666666667 |
| net/core/skbuff.c:577 | 9 | 10679975 | 1186663.888888889 |
| net/core/skbuff.c:658 | 21 | 11013437 | 524449.380952381 |
| fs/select.c:168 | 7 | 2831226 | 404460.85714285716 |
| lib/alloc_tag.c:51 | 1 | 340649 | 340649.0 | <--- Here I started
| kernel/signal.c:455 | 1 | 300730 | 300730.0 |
| fs/notify/inotify/inotify_fsnotify.c:96 | 1 | 249831 | 249831.0 |
| fs/ext4/dir.c:675 | 3 | 519734 | 173244.66666666666 |
| drivers/usb/host/xhci.c:1555 | 4 | 126402 | 31600.5 |
| fs/locks.c:275 | 36 | 986957 | 27415.472222222223 |
| fs/proc/inode.c:502 | 3 | 63753 | 21251.0 |
| fs/pipe.c:125 | 123 | 2143378 | 17425.837398373984 |
| net/core/scm.c:84 | 3 | 43267 | 14422.333333333334 |
| fs/kernel_read_file.c:80 | 2 | 26910 | 13455.0 |
+-----------------------------------------+-------+------------------+--------------------+

I think this is another "good" usage for cumulative counters: if a module just keeps alloc/free memory,
maybe it is good to move the memory alloc/free to somewhere less frequent.

In the case of this patch, a memory allocation for each read-calls, can be moved to opan-calls.

If interested, I can re-send the patch for cumulative counters for further discussions.

FYI
David