linux-kernel - Re: [PATCH v1 0/2] mm/show_mem: Bug fix for print mem alloc info

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Message-ID: <aK9htWRehfJDLFJD@fedora>
Date: Wed, 27 Aug 2025 12:51:17 -0700
From: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
To: Yueyang Pan <pyyjason@...il.com>
Cc: Suren Baghdasaryan <surenb@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>, 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 0/2] mm/show_mem: Bug fix for print mem alloc info

On Wed, Aug 27, 2025 at 11:34:21AM -0700, Yueyang Pan wrote:
> This patch set fixes two issues we saw in production rollout. 
> 
> The first issue is that we saw all zero output of memory allocation 
> profiling information from show_mem() if CONFIG_MEM_ALLOC_PROFILING 
> is set and sysctl.vm.mem_profiling=0. In this case, the behaviour 
> should be the same as when CONFIG_MEM_ALLOC_PROFILING is unset, 

Did you mean to say when sysctl.vm.mem_profiling=never?

My understanding is that setting the sysctl=0 Pauses memory allocation
profiling, while 1 Resumes it. When the sysctl=never should be the same
as when the config is unset, but I suspect we might still want the info
when set to 0.

> where show_mem prints nothing about the information. This will make 
> further parse easier as we don't have to differentiate what a all 
> zero line actually means (Does it mean  0 bytes are allocated 
> or simply memory allocation profiling is disabled).
> 
> The second issue is that multiple entities can call show_mem() 
> which messed up the allocation info in dmesg. We saw outputs like this:  
> ```
>     327 MiB    83635 mm/compaction.c:1880 func:compaction_alloc
>    48.4 GiB 12684937 mm/memory.c:1061 func:folio_prealloc
>    7.48 GiB    10899 mm/huge_memory.c:1159 func:vma_alloc_anon_folio_pmd
>     298 MiB    95216 kernel/fork.c:318 func:alloc_thread_stack_node
>     250 MiB    63901 mm/zsmalloc.c:987 func:alloc_zspage
>     1.42 GiB   372527 mm/memory.c:1063 func:folio_prealloc
>     1.17 GiB    95693 mm/slub.c:2424 func:alloc_slab_page
>      651 MiB   166732 mm/readahead.c:270 func:page_cache_ra_unbounded
>      419 MiB   107261 net/core/page_pool.c:572 func:__page_pool_alloc_pages_slow
>      404 MiB   103425 arch/x86/mm/pgtable.c:25 func:pte_alloc_one
> ```
> The above example is because one kthread invokes show_mem() 
> from __alloc_pages_slowpath while kernel itself calls 
> oom_kill_process()

I'm not familiar with show_mem(). Could you spell out what's wrong with
the output above?

> Yueyang Pan (2):
>   mm/show_mem: No print when not mem_alloc_profiling_enabled()
>   mm/show_mem: Add trylock while printing alloc info
> 
>  mm/show_mem.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> -- 
> 2.47.3
>