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From: Shakeel Butt To: Jingxiang Zeng Cc: linux-mm@kvack.org, akpm@linux-foundation.org, hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, muchun.song@linux.dev, chengming.zhou@linux.dev, kasong@tencent.com, kernel test robot Subject: Re: [PATCH] mm/list_lru: make the case where mlru is NULL as unlikely Message-ID: References: <20250225153020.2514685-1-jingxiangzeng.cas@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250225153020.2514685-1-jingxiangzeng.cas@gmail.com> X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Queue-Id: 813DF4001E X-Rspamd-Server: rspam07 X-Stat-Signature: mkjmqp9co3d5jchsz3axik6d4tmcw4yb X-HE-Tag: 1740500598-697991 X-HE-Meta: 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 bTxgWOl3 sZ3u38UkPJ+xCbFBm7CPKoJV5KdNhQ4syeROjtXjkl4ZvxE0TYdRf6r9loKPiq1FHlTCJL3+qZoxp9MEn7NREEOOA5BMFRinQHA4ClyLWJ2WmxHcsgFwJPYxkKPso3HXDo7QflkANpJo4Yh7ThmQ9xZHjFkfN2H+YjTG5F9qWYf+MXWI3KsDBz6HMHbulbviCiKd91Oz4NkwF1YhQ9YOiXsd2/hWJuTG6bbAgH3lgmTwNssd03Y3IOBwXiKU+nY9587o2w7C06I/pG9tq5VMaNi+EQ5dJgWfgpT5kCh7jy6+VwmI= 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 Tue, Feb 25, 2025 at 11:30:20PM +0800, Jingxiang Zeng wrote: > From: Zeng Jingxiang > > In the following memcg_list_lru_alloc() function, mlru here is almost > always NULL, so in most cases this should save a function call, mark > mlru as unlikely to optimize the code. > do { > xas_lock_irqsave(&xas, flags); > if (!xas_load(&xas) && !css_is_dying(&pos->css)) { > xas_store(&xas, mlru); > if (!xas_error(&xas)) > mlru = NULL; > } > xas_unlock_irqrestore(&xas, flags); > } while (xas_nomem(&xas, GFP_KERNEL)); > > if (mlru) > kfree(mlru); > > Reported-by: kernel test robot > Closes: https://lore.kernel.org/oe-kbuild-all/202412290924.UTP7GH2Z-lkp@intel.com/ > Signed-off-by: Zeng Jingxiang > --- > mm/list_lru.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/list_lru.c b/mm/list_lru.c > index 064d2018e265..e7e13513ff8e 100644 > --- a/mm/list_lru.c > +++ b/mm/list_lru.c > @@ -552,7 +552,7 @@ static int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru) > } > xas_unlock_irqrestore(&xas, flags); > } while (xas_nomem(&xas, GFP_KERNEL)); > - if (mlru) > + if (unlikely(mlru)) > kfree(mlru); The report is saying not to check at all. So, just remove the check and simply call kfree(mlru) as it handles the NULL check efficiently. > set_active_memcg(cur); > } while (pos != memcg && !css_is_dying(&pos->css)); > -- > 2.43.5 > >