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 AEA372264A3; Fri, 4 Sep 2026 05:42:29 +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=1788500550; cv=none; b=VP7Ywqb8jKpjA9/AceGkR/1azSt4Xp9fmyXp4sG2fEfR4lngh8UBH0ceQNs3alPiQ714vF11GPF2oZP4taCxCzzBJG6tUrpVp9MIjkNS3oW3203kWVc7fAx6PvKb4nV6Apt6lhxzfJ+h/PnteU5o2cheueMkCcS053FRkwPI2DM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788500550; c=relaxed/simple; bh=EcZsdHHUSt1RU88b+CKGggyGCNURIeBwvWeyMglHXTY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=UwwT7oYPyv9wXkVUnPyvhRWmFJjlMLMox9CD1coCjqSRWJV2FK1Tk6LMiV6Je1QuGKCG6BuCE6gkH02LjGP62erSxEUyGrWSZ0mDKIP3VrEcHjAznzWLSI5HNnZ/Kbm71TuHBATnqFVnxXMyFsoP4KxbdITuJ/tddql6F+AxOSA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=eCbr8D9y; 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="eCbr8D9y" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 156561F00A3D; Fri, 4 Sep 2026 05:42:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1788500549; bh=aEYB1DY0JFkHxCtsE20wPcBzU4aoO3AH9mIA91jv2PY=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=eCbr8D9yip8gKEwecbuvJn/XXRLhvdFhrcFC8HYPaTCTCxMWdGhYGp4dpM6t6s0CX 3AxY3cB4d+9ur1W7XeZuI2xsnr3scQHHC2rXqWuFzlvb5sxromBGRhoCRfYeQ6Hl49 gXXe32hGP6+f9o2PFOVA1Dkp4NN8aBELiW+LAQSs= 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 6.18 096/552] zsmalloc: account for handle size in class lookup Date: Fri, 4 Sep 2026 06:54:13 +0200 Message-ID: <20260904045750.073798710@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260904045747.813364717@linuxfoundation.org> References: <20260904045747.813364717@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 6.18-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 @@ -508,6 +508,11 @@ 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) { @@ -1052,7 +1057,7 @@ 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; } @@ -1279,9 +1284,7 @@ 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);