From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f52.google.com (mail-pj1-f52.google.com [209.85.216.52]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E073478F59 for ; Wed, 22 Apr 2026 00:35:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.52 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776818133; cv=none; b=cBGu/rmXixO9WwOCdwOvmu6cv9YE4C39OrBUkyXCqJB/BLMUXSNxRPK1/tOBMKX8iWHCdRdjoGvyJFaAU5awT3oKF6ntGKQiruJfOErPTS18FyUFEScHmUENXKVbc7ONeNAeMQ4oKsbw8VEjOo+RGvs33UMMauTLMJ7EA2pTebk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776818133; c=relaxed/simple; bh=Z9ililjLGwtjtq0BjJzya7bvG160JiMRbUiNNtS4wb0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=iyPAiwTz+vxGR+9caqNwsBJwdCqRMsDtiRkcSJ4iXdQf3lHxF+1YmvZ955eow/1XvoR3hFd5hWwWPnu2w8aWucHYwlDNJNJZvAGlsc6mkGGSziI86tBMylOPSmL/05bogDuJdwTzvoVWusDMz21z5RDRH/xGtDjgGMRGUFfqTOI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=KzZBygMz; arc=none smtp.client-ip=209.85.216.52 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="KzZBygMz" Received: by mail-pj1-f52.google.com with SMTP id 98e67ed59e1d1-362ba069b13so215201a91.2 for ; Tue, 21 Apr 2026 17:35:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1776818131; x=1777422931; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=lVYBYcbMKP9T66v2BVVHPkUpnYU8ZtQu2qMfVc8wIjw=; b=KzZBygMz6y+G3viPbrCWIEOlX4IKbn/LojmTTmdygL7GBjvQ2IaVUbvC7GxYHlls8M xEwQoOS/sMhs8Ol/kkhsKSlIslG1isOqORXlX22GjxtBBAjdPi/xdvjoznjZyPCvBg5f 4NHs0UD3G0sX9Jjo/7lfkFnDqSRTnzDnTzxPtfnIRj6Lmn4GnaempHOCGWfP+lvLh0L9 AyOpClkBXCj4q6W0rfZodqkk68ip8FPaPTRrAKfcsG6UtjvchMziuK/PQ+w7d6fuSODW vTfUJGeSS+mmie/RSrdeSt+spH87M1fcYpuD01CioLjRnFxZweYyjmAPsqIB0KMKsnOk YriQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1776818131; x=1777422931; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=lVYBYcbMKP9T66v2BVVHPkUpnYU8ZtQu2qMfVc8wIjw=; b=M1VtvoO7PFyc/WtNVpGkiU3Wy6qbp5AtDMBJmCyXyZm9JUdC6KEmjoqjUmnw9eZD/6 EcrxVH+dMzzvxeHdXbxAttxDJeS79/RVSg4OBK/j/Jd0QjdDtsS0MjXDf6x5z6PC+EFm t7VLXI3/l7EeZ3qIsPaab9UVDWVfysM3hHJYiwM4i44D7BYQbrLw15c/2NjdGgf4a3cB Z53CqDzwDMTakzw8xcGGCdAu8Ok/wCFwwsN7QkoLMGXvFBk5JxVEfbgsq53jhNq/q5ay vnZBV4JlfZIa+1LDaP/Ng1HBJuKXcjJ50M/829NDbprZ0mZ1sRqHaqeVZf1xUQ5YwSAk rXRQ== X-Forwarded-Encrypted: i=1; AFNElJ/HOgilB1fkg6etlmxOGGDTHsWYUYb40WzbfX9jp/6JxxONHImu3WA8trRZGRr3w35Wh4rPhXH7LxmH2Q==@vger.kernel.org X-Gm-Message-State: AOJu0YwAeBZhMr4dt207++xQgNs7mxxU93+sWhiMh03VunVIAzdgZFIR PiMD65HzsRRWA54qY+eDkQ7JudfEyVYAuPyWuuk58FbmzWmwiUqS7K0a X-Gm-Gg: AeBDies5phwpL/cCeQJLZ7I+FL0dWA6FiJlKbw4C0Uqm6WvPEfaw1ALoxZojMR+tAeH 8xe5f+GNOMQy5PrCXRvfVPUVs5kxY27Kf2Sftl+7u9y6QOeCi86PswSBlqmXjBvTIKHs4xF3x3U IsHXwmgLPcQn1wCpSat3crEYYLd9i6VeK+Nq1Gyq+xSpC0N5DzSI5rBfjZaWM45MGYyYKDmnl1l s4QESMEuPUm3INQtmfGXH+mmTBI1vyztg+mjA7r4KSM6jNl1CD5GIwzRawQllrdrZxkl233QOMf VpTLX3lhtNKQODGj7DRjBnCap9X+x9+CktUPhHnjaPU64ZnV+2BAKaJjsj6CgrMMVj66YwHH2Rw oB9Lc9ow0locM48uQDQfeiCm8JBtduxcrZ10oYFPdO0AzIhPvE/ItQpPIxdz7nXiCE8/qwYPQ+Z NUASnfLnkt+1d0NW6RbX3cCvmtH4HRklzCMSloaEO6QdiQFKhtkKmey90msGIwyl/lKsy1LCZDX dtnpN2bm7Djv8zwrujQVw== X-Received: by 2002:a05:6a21:62cc:b0:39b:91d1:6c10 with SMTP id adf61e73a8af0-3a08d916aa1mr11415454637.4.1776818130499; Tue, 21 Apr 2026 17:35:30 -0700 (PDT) Received: from fedora ([188.253.4.228]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c79770512afsm11597247a12.31.2026.04.21.17.35.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Apr 2026 17:35:30 -0700 (PDT) From: Xueyuan Chen To: nphamcs@gmail.com Cc: ryncsn@gmail.com, haowenchao22@gmail.com, akpm@linux-foundation.org, chengming.zhou@linux.dev, axboe@kernel.dk, hannes@cmpxchg.org, minchan@kernel.org, senozhatsky@chromium.org, yosry@kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, baohua@kernel.org, xueyuan.chen21@gmail.com, haowenchao@xiaomi.com Subject: Re: [RFC PATCH v2 0/4] mm/zsmalloc: reduce zs_free() latency on swap release path Date: Wed, 22 Apr 2026 08:34:12 +0800 Message-ID: <20260422003412.11678-1-xueyuan.chen21@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Tue, Apr 21, 2026 at 11:25:17AM -0700, Nhat Pham wrote: [...] >Hmm, free_zspage() and kmem_cache_free(). > >* kmem_cache_free() is just handle freeing. Bulk-freeing? > >* free_zspage() looks like just ordinary teardown work :( Seems like >we're not spinning any lock here - we just try lock the backing pages, >and the rest is normal work. Not sure how to optimize this - perhaps >deferring is the only way. > > Hi Nhat, Currently, free_zspage() is called while holding the class->lock. However, free_zspage() eventually invokes folio_put(), which may acquire the zone->lock. This creates a nested lock dependency. If multiple CPUs contend for the same class->lock and the current holder is stalled waiting for the zone->lock, it significantly extends the hold time of the class->lock. This causes other CPUs to wait much longer. Here is the ftrace data showing the severe contention on class->lock. Under contention, the time spent in queued_spin_lock_slowpath() jumps from ~1.3us to over 30us, significantly increasing the total latency of zs_free(). 7) | zs_free() { 7) 0.220 us | _raw_read_lock(); 7) | _raw_spin_lock() { 7) 1.320 us | queued_spin_lock_slowpath(); 7) 1.820 us | } 7) 0.170 us | _raw_read_unlock(); 7) 0.170 us | obj_free(); 7) 0.190 us | fix_fullness_group(); 7) 0.150 us | _raw_spin_unlock(); 7) 0.170 us | kmem_cache_free(); 7) 4.610 us | } --------------------------------------------------------- 7) | zs_free() { 7) 0.230 us | _raw_read_lock(); 7) | _raw_spin_lock() { 7) + 30.100 us | queued_spin_lock_slowpath(); 7) + 30.600 us | } 7) 0.200 us | _raw_read_unlock(); 7) 0.170 us | obj_free(); 7) 0.170 us | fix_fullness_group(); 7) 0.170 us | _raw_spin_unlock(); 7) 0.210 us | kmem_cache_free(); 7) + 33.850 us | } Best regards, Xueyuan