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Tue, 23 Jan 2024 11:03:56 GMT Received: from [10.214.66.119] (10.80.80.8) by nalasex01a.na.qualcomm.com (10.47.209.196) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.40; Tue, 23 Jan 2024 03:03:54 -0800 Message-ID: <56154bf4-c1e2-16d5-c6e2-c2dee42d3377@quicinc.com> Date: Tue, 23 Jan 2024 16:33:51 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Content-Language: en-US From: Charan Teja Kalla To: , Matthew Wilcox CC: "linux-mm@kvack.org" , LKML Subject: Purpose of maple_node objects to be its size aligned X-ClientProxiedBy: nasanex01b.na.qualcomm.com (10.46.141.250) To nalasex01a.na.qualcomm.com (10.47.209.196) X-QCInternal: smtphost X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=5800 signatures=585085 X-Proofpoint-GUID: hCX1sMD41WRuH3wU0PexQVokd9gePt1y X-Proofpoint-ORIG-GUID: hCX1sMD41WRuH3wU0PexQVokd9gePt1y X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.1011,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2024-01-23_05,2024-01-23_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 spamscore=0 mlxlogscore=998 clxscore=1011 impostorscore=0 malwarescore=0 suspectscore=0 bulkscore=0 adultscore=0 phishscore=0 mlxscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2311290000 definitions=main-2401230080 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1788879036210212136 X-GMAIL-MSGID: 1788879036210212136 I am just curious about the purpose of maple node slab objects to be its size aligned, but I can understand why they need to be cache aligned. void __init maple_tree_init(void) { maple_node_cache = kmem_cache_create("maple_node", sizeof(struct maple_node), sizeof(struct maple_node),// Alignment of the slab object. SLAB_PANIC, NULL); } Reason for the ask is, when slub debug enabled with option Z, the change [1] makes the total object to be 256 * 3 (=768)bytes. This turns out to be a problem in debug builds where the unreclaimable slab consumption itself is very high thus exerting the memory pressure on the system. maple_node: orginal object size = 256b after slub_debug enabled = 768b If, there is no special requirement, other than just needs to be cache aligned, thinking of the below: [1]d86bd1bece6f ("mm/slub: support left redzone") Thanks, charan --- a/lib/maple_tree.c +++ b/lib/maple_tree.c @@ -6283,8 +6283,8 @@ bool mas_nomem(struct ma_state *mas, gfp_t gfp) void __init maple_tree_init(void) { maple_node_cache = kmem_cache_create("maple_node", - sizeof(struct maple_node), sizeof(struct maple_node), - SLAB_PANIC, NULL); + sizeof(struct maple_node), 0, + SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL); }