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Thu, 16 Apr 2026 00:41:26 -0700 (PDT) Received: from google.com ([2a00:79e0:2031:6:63b6:f9e5:485d:ef04]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-36132cfc6cdsm1654717a91.13.2026.04.16.00.41.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 16 Apr 2026 00:41:26 -0700 (PDT) Date: Thu, 16 Apr 2026 16:41:22 +0900 From: Sergey Senozhatsky To: Xueyuan Chen Cc: ryncsn@gmail.com, baohua@kernel.org, minchan@kernel.org, senozhatsky@chromium.org, akpm@linux-foundation.org, linux-mm@kvack.org, axboe@kernel.dk, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, kasong@tencent.com, chrisl@kernel.org, justinjiang@vivo.com, liulei.rjpt@vivo.com Subject: Re: [RFC PATCH] zram: support asynchronous GC for lazy slot freeing Message-ID: References: <20260414054930.225853-1-xueyuan.chen21@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260414054930.225853-1-xueyuan.chen21@gmail.com> On (26/04/14 13:49), Xueyuan Chen wrote: > On Sun, Apr 12, 2026 at 07:48:48PM +0800, Kairui Song wrote: > [...] > >What is making this slot_free so costly? zs_free? > > Yes, I've captured some perf data on RK3588 cpu2: > > - 3.79% 0.42% zram [zram] [k] slot_free > - 89.04% slot_free > - 65.40% zs_free > + 77.29% free_zspage > + 21.75% kmem_cache_free > 0.68% __kern_my_cpu_offset > + 13.19% _raw_spin_unlock > + 4.86% _raw_read_unlock > 4.75% obj_free > + 4.72% _raw_read_lock > 3.64% fix_fullness_group > + 2.02% _raw_spin_lock > + 1.31% kmem_cache_free > > It's clear that zs_free is the primary hotspot, accounting for ~65.40% > of the total slot_free cycles. Beyond that, have some read and spin lock > in slot_free. Just a random thought, if zs_free() is costly then it likely also affects zswap, which makes me wonder if doing something on the zsmalloc side is a "batter" way forward.