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

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Message-ID: <aLDTu3GrvLd9jMhr@devbig569.cln6.facebook.com>
Date: Thu, 28 Aug 2025 15:10:03 -0700
From: Yueyang Pan <pyyjason@...il.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Brendan Jackman <jackmanb@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>, Zi Yan <ziy@...dia.com>,
	Usama Arif <usamaarif642@...il.com>, linux-mm@...ck.org,
	kernel-team@...a.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] mm/show_mem: Add trylock while printing alloc info

On Thu, Aug 28, 2025 at 11:54:58AM +0200, Vlastimil Babka wrote:
> 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@...il.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.

Cool. Then I will do this for the previous part before memory allocation info.

> 
> > Thanks
> > Pan
>