From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2D77F418A2D; Fri, 4 Sep 2026 06:07:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788502039; cv=none; b=puIcWh9vOw6FwXzXO5auZVzxeUOIGSTBVz50r0XjV6eNrRm4WBlFGeHueqQXnqiCOfts+GBTd46eQsK0/Rxu3xa4BW+/BLkgNz73xYXP0a3grF1Olw/i98RgoddhVC3qXARRoR5cp0Fche1OFSUAA5ujIwPe62O+ssAu+rXrg/Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788502039; c=relaxed/simple; bh=T+AMsNccLnVh9TmSzt6T5his4BKOVwOfe6fIhUTJtow=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=teR/PqqblJlmoUiFSP2+oGh3l6r/kYvH7dZKs2J5aE6gzNf2Nc182RF8Th3uIgba69cJgdq8ve4XnM7GF58T7lkyl+rku8LNqgGjocE6eajS7Sm2MeraxXgcFOpOiDnFvwLL7ScRhDobxYVaoOK3rj2Zt2Ks2RcKwYl0Z2MlvTY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=c49oTmM7; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="c49oTmM7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 406911F00A3D; Fri, 4 Sep 2026 06:07:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1788502036; bh=tdW0A/C7mSeFhJaPqR8W9afyC6vshNZeVnXha2I8Nyo=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=c49oTmM7aeedirtzfzbiUtkdncs8ShTdLFseK0nMkIq8sN9iNaWi35EJolG+WNDnv uAtgYxO0kDIfPnX0a7/FVYvUUnGUpBq8/scPvFORslTpsiu6Svye9TqzGHG5NOhMiU PsBwfNRQfM04yT4Vng7doLs5rcm7di3oIy3Ro9fI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Longlong Xia , Sergey Senozhatsky , Minchan Kim , Andrew Morton Subject: [PATCH 6.12 067/403] zsmalloc: account for handle size in class lookup Date: Fri, 4 Sep 2026 06:57:50 +0200 Message-ID: <20260904045736.359634760@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260904045734.806166532@linuxfoundation.org> References: <20260904045734.806166532@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Longlong Xia commit f7bf5cd5b5f2b13fe2361860880c4e214c08b440 upstream. zs_lookup_class_index() lets zram recompression decide whether a newly compressed object would use a smaller size class. It currently classifies the payload size directly, while zs_malloc() adds ZS_HANDLE_SIZE before selecting the class. This makes lookup disagree with allocation near size-class boundaries. With 4 KiB pages, CONFIG_ZSMALLOC_CHAIN_SIZE=8, and 64-bit handles, a 1025-to-1024-byte recompression appears to move from class 64 to class 62 although both allocations use class 64. Conversely, a 1049-to-1025-byte recompression appears to stay in class 64 although the allocations move from class 65 to class 64. As a result, zram can accept replacements with no allocation benefit or reject ones that would save memory, potentially marking the object incompressible. Factor size-class selection into lookup_size_class(), account for the handle there, and use the helper for both lookup and allocation. Link: https://lore.kernel.org/20260809115518.3791787-1-xialonglong2025@163.com Fixes: 7c2af309abd2 ("zram: add size class equals check into recompression") Assisted-by: Codex:gpt-5.6-sol Signed-off-by: Longlong Xia Reviewed-by: Sergey Senozhatsky Cc: Minchan Kim Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/zsmalloc.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -515,6 +515,11 @@ static int get_size_class_index(int size return min_t(int, ZS_SIZE_CLASSES - 1, idx); } +static struct size_class *lookup_size_class(struct zs_pool *pool, size_t size) +{ + return pool->size_class[get_size_class_index(size + ZS_HANDLE_SIZE)]; +} + static inline void class_stat_add(struct size_class *class, int type, unsigned long cnt) { @@ -1156,7 +1161,7 @@ unsigned int zs_lookup_class_index(struc { struct size_class *class; - class = pool->size_class[get_size_class_index(size)]; + class = lookup_size_class(pool, size); return class->index; } @@ -1368,9 +1373,7 @@ unsigned long zs_malloc(struct zs_pool * if (!handle) return (unsigned long)ERR_PTR(-ENOMEM); - /* extra space in chunk to keep the handle */ - size += ZS_HANDLE_SIZE; - class = pool->size_class[get_size_class_index(size)]; + class = lookup_size_class(pool, size); /* class->lock effectively protects the zpage migration */ spin_lock(&class->lock);