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Thu, 28 Aug 2025 01:47:49 -0700 (PDT) Received: from devbig569.cln6.facebook.com ([2a03:2880:31ff:74::]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3cbc6a5da6dsm9463817f8f.63.2025.08.28.01.47.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 Aug 2025 01:47:48 -0700 (PDT) Date: Thu, 28 Aug 2025 01:47:46 -0700 From: Yueyang Pan To: Vlastimil Babka Cc: Andrew Morton , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Usama Arif , linux-mm@kvack.org, kernel-team@meta.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v1 2/2] mm/show_mem: Add trylock while printing alloc info Message-ID: References: <7e2bc96faab1a338829e549246189ad96e6c866b.1756318426.git.pyyjason@gmail.com> <20250827150619.4e468e68988f224f9f9bea6f@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 2718C180009 X-Stat-Signature: md8yq3rig4g87qe899r15cqoj5yycr9m X-Rspam-User: X-HE-Tag: 1756370870-128884 X-HE-Meta: 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 I/wXln5W 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 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. 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? > > >> > > >> > >> Fair enough, I guess. > >> > >> > --- a/mm/show_mem.c > >> > +++ b/mm/show_mem.c > >> > @@ -23,6 +23,8 @@ EXPORT_SYMBOL(_totalram_pages); > >> > unsigned long totalreserve_pages __read_mostly; > >> > unsigned long totalcma_pages __read_mostly; > >> > > >> > +static DEFINE_MUTEX(mem_alloc_profiling_mutex); > >> > >> It would be a bit neater to make this local to __show_mem() - it didn't > >> need file scope. > > > > Thanks for your feedback, Andrew. I will move it the next version. > > > >> > >> Also, mutex_unlock() isn't to be used from interrupt context, so > >> problem. > >> > >> Something like atomic cmpxchg or test_and_set_bit could be used and > >> wouldn't involve mutex_unlock()'s wakeup logic, which isn't needed > >> here. > > > > I was not aware of interrupt context before. I will change to test-and-set > > lock in the next version. > > Perhaps simply spinlock_t with spin_trylock()? > Agreed. Thanks Pan