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

David Wang
2025-05-08T02:25:28Z

At 2025-05-08 07:42:56, "Suren Baghdasaryan" <surenb@google.com> wrote:
>On Wed, May 7, 2025 at 6:19 PM David Wang <00107082@163.com> wrote:
>>
>> 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.
>
>Yeah, my issue with cumulative counters is that while they might be
>useful for some analyses, most usecases would probably not benefit
>from them while sharing the performance overhead. OTOH making it
>optional with a separate CONFIG that affects the content of the
>/proc/allocinfo seems like a bad idea to me. Userspace parsers now
>would have to check not only the file version but also whether this
>kernel config is enabled, or handle a possibility of an additional
>column in the output. Does not seem like a good solution to me.

Thanks for the quick feedback~
Agree that this would cause troubles to userspace tools,
and also it add more performance impact for profiling.

David

>
>All that said, I'm open to suggestions if there is a way to
>incorporate cumulative counters that would not tax all other usecases
>that do not need them.
>
>>
>>
>> FYI
>> David