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Tue, 27 Feb 2024 17:57:24 -0800 (PST) Received: from google.com ([2401:fa00:8f:203:f4f0:fb4d:aa01:9068]) by smtp.gmail.com with ESMTPSA id sv8-20020a17090b538800b0029658c7bd53sm239765pjb.5.2024.02.27.17.57.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Feb 2024 17:57:24 -0800 (PST) Date: Wed, 28 Feb 2024 10:57:20 +0900 From: Sergey Senozhatsky To: Chengming Zhou Cc: yosryahmed@google.com, Sergey Senozhatsky , hannes@cmpxchg.org, nphamcs@gmail.com, Andrew Morton , Minchan Kim , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 0/2] mm/zsmalloc: simplify synchronization between zs_page_migrate() and free_zspage() Message-ID: <20240228015720.GC11972@google.com> References: <20240226-zsmalloc-zspage-rcu-v1-0-456b0ef1a89d@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240226-zsmalloc-zspage-rcu-v1-0-456b0ef1a89d@bytedance.com> X-Rspamd-Queue-Id: 1C7D91C0005 X-Rspam-User: X-Stat-Signature: 65jm373qm9kzreagmx9b9tdz8yytfd1q X-Rspamd-Server: rspam03 X-HE-Tag: 1709085445-261741 X-HE-Meta: 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 AGQaRpkD oDTQtoZmLa9KIQADF3GzNqP+Dqc2CobxG5F7SXUQK8MNhMPdlSKDQdj2GUcEiS1MCEE2dXOAn+Rsug+pZgbmxoUp5OA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.001662, 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 (24/02/27 03:02), Chengming Zhou wrote: > Hello, > > free_zspage() has to hold locks of all pages, since zs_page_migrate() > path rely on this page lock to protect the race between zs_free() and > it, so it can safely get zspage from page->private. > > But this way is not good and simple enough: > > 1. Since zs_free() couldn't be sleepable, it can only trylock pages, > or has to kick_deferred_free() to defer that to a work. > > 2. Even in the worker context, async_free_zspage() can't simply > lock all pages in lock_zspage(), it's still trylock because of > the race between zs_free() and zs_page_migrate(). Please see > the commit 2505a981114d ("zsmalloc: fix races between asynchronous > zspage free and page migration") for details. > > Actually, all free_zspage() needs is to get zspage from page safely, > we can use RCU to achieve it easily. Then free_zspage() don't need to > hold locks of all pages, so don't need the deferred free mechanism > at all. This patchset implements it and remove all of deferred free > related code. > > Thanks for review and comments! > > Signed-off-by: Chengming Zhou JFI, recovered from the SPAM folder "The sender hasn't authenticated this message"