Re: [PATCH v1 2/2] mm/show_mem: Add trylock while printing alloc info

[Vlastimil Babka <vbabka@suse.cz>]

On 8/28/25 11:51, Yueyang Pan wrote:
> On Thu, Aug 28, 2025 at 10:53:01AM +0200, Vlastimil Babka wrote:
>> On 8/28/25 10:47, Yueyang Pan wrote:
>> > On Thu, Aug 28, 2025 at 10:41:23AM +0200, Vlastimil Babka wrote:
>> >> On 8/28/25 10:34, Yueyang Pan wrote:
>> >> > On Wed, Aug 27, 2025 at 03:06:19PM -0700, Andrew Morton wrote:
>> >> >> On Wed, 27 Aug 2025 11:34:23 -0700 Yueyang Pan <pyyjason@gmail.com> wrote:
>> >> >> 
>> >> >> > In production, show_mem() can be called concurrently from two
>> >> >> > different entities, for example one from oom_kill_process()
>> >> >> > another from __alloc_pages_slowpath from another kthread. This
>> >> >> > patch adds a mutex and invokes trylock before printing out the
>> >> >> > kernel alloc info in show_mem(). This way two alloc info won't
>> >> >> > interleave with each other, which then makes parsing easier.
>> >> 
>> >> What about the rest of the information printed by show_mem() being interleaved?
>> > 
>> > Thanks for your feedback, Vlastimil. We cannot use trylock for the rest 
>> > part as node filter can be different.
>> 
>> Right.
>> 
>> > Do you think we need a lock to prevent the whole show_mem() from being 
>> > interleaved and to acquire it at the very beginning? Will it be too 
>> > heavy?
>> 
>> It might be risky so perhaps let's not. Guess we can disentangle by dmesg
>> showing the thread id prefix.
> 
> I have thought about this. Since each line can interleave with another, we 
> would end up adding tid to each line. Not sure if this is acceptable.

I meant that printk/dmesg already does that so it's fine.

> Thanks
> Pan