Re: [PATCH v2] mm: slub: Convert sys slab alloc_calls, free_calls to bin attribute

[Faiyaz Mohammed <faiyazm@codeaurora.org>]

Hi,

Sorry for late response!

On 3/2/2021 6:41 PM, Greg Kroah-Hartman wrote:
> On Tue, Mar 02, 2021 at 01:59:46PM +0100, Vlastimil Babka wrote:
>> On 2/17/21 7:31 AM, Faiyaz Mohammed wrote:
>>> Reading the sys slab alloc_calls, free_calls returns the available object
>>> owners, but the size of this file is limited to PAGE_SIZE
>>> because of the limitation of sysfs attributes, it is returning the
>>> partial owner info, which is not sufficient to debug/account the slab
>>> memory and alloc_calls output is not matching with /proc/slabinfo.
>>>
>>> To remove the PAGE_SIZE limitation converted the sys slab
>>> alloc_calls, free_calls to bin attribut
>>>
>>> Signed-off-by: Faiyaz Mohammed <faiyazm@codeaurora.org>
>>
>> After discussing this with Greg and PeterZ, sysfs should be one value per file,
>> and is just not proper API for this kind of info. We should reimplement at least
>> these clearly debugging "attributes" in debugfs, where they belong, instead of
>> trying to hack around the limitation in sysfs.
> 
> sysfs is _REQUIRED_ to be "one value per file", any kernel code that
> abuses this needs to be fixed up.
> 
> Why are these slab files in sysfs at all anyway?  They all feel like
> debugging stuff to me, why not move everything to debugfs?  Would make
> for a lot less code overall.
> 
Yes, we can move the /sys/kernel/slab/kmemcache/alloc_calls and
/sys/kernel/slab/kmemcache/free_calls implementation to debugfs but is
it okay to move only alloc_calls and free_calls? or we have to move
whole sysfs interface to debugfs?.

If we are moving only alloc_calls/free_calls interface to debugfs then I
think we can add all slab objects data into single file.

For example: /sys/kernel/debugfs/slab/alloc_calls, which will print all
slab objects data.

Example Output: alloc_list: call_site=__request_region+0xb4/0x2f0
count=228 object_size=128 slab_size=640 slab_name=kmalloc-128

or

We can have just like current sysfs interface, have separate
alloc_calls/free_calls traces per kmem cache.

Which one would be better?.

> 

Thanks and regards,
Mohammed Faiyaz