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Tue, 1 Sep 2026 03:12:48 +0000 (UTC) Received: from fedora.redhat.corp (headnet05.pony-001.prod.iad2.dc.redhat.com [10.2.32.117]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 0AE9B18005B8; Tue, 1 Sep 2026 03:12:43 +0000 (UTC) From: Luiz Capitulino To: linux-kernel@vger.kernel.org, linux-mm@kvack.org, david@kernel.org, baolin.wang@linux.alibaba.com, ziy@nvidia.com, lance.yang@linux.dev Cc: corbet@lwn.net, tsbogend@alpha.franken.de, maddy@linux.ibm.com, mpe@ellerman.id.au, agordeev@linux.ibm.com, gerald.schaefer@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, x86@kernel.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, hughd@google.com, dave.hansen@linux.intel.com, djbw@kernel.org, vishal.l.verma@intel.com, dave.jiang@intel.com, akpm@linux-foundation.org, yintirui@huawei.com, dev.jain@arm.com, usama.arif@linux.dev Subject: [PATCH v7 02/14] mm: shmem: shmem_getattr(): set blksize to highest supported THP order Date: Mon, 31 Aug 2026 23:12:06 -0400 Message-ID: <4d61dc5e8d6ffe957020eb34f57fb51099c2913b.1788232334.git.luizcap@redhat.com> In-Reply-To: References: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 X-Mimecast-MFC-PROC-ID: dH8JCpB5ciu5-JDqHl5-nRv0gVJp8RiXO2z0pOx5thA_1788232370 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: BB35B40002 X-Stat-Signature: mzr7ma91e81jfubaro8iyh93iwgzrxfp X-Rspam-User: X-HE-Tag: 1788232377-34424 X-HE-Meta: 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 9FiayA2Q dZNV16OfOFTnofNCKw4gmFnaE/SwtWVmgMcrgMQLsVwyrsOUERcsorRAYYXF4Zykfzd/52xCsGRcPCUIAC8RE5ZsB4Elumvk+se7uttkNvZ6ATQV4sYYPpeDG9UHE4NJg3wtrTSjE+fyZxyjOCfnjYZUs6m9r1pLT+pqJEFrZAq0rEBOibXpOlXffIcfNjSRv7nw2pWg5666ymvRcalezDCqJRG2ULQAHIFjf5UURfvWo9SbNlCIvepR2fN/th8j/Mm7ihX2JEJk4cV5cYHe/46LicOw1l7ApZbY1w4Wk6icaSUAzc1y4wSS5n5sOeWExX38vADe4YAu3T7Ye3+g9O3b3R6DqNP3ZH+9W9nNc9oJJiJUVhaiCWHNZaZAWsPLRhTz0vMr6Jif814v72mhR9Wj9d3ekUPTBrkWogEcg6klbT3S3cHX27WZ3i0b6F8TSEjvLHt6B6zV5WB0= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Today, shmem_getattr() sets stat->blksize to PMD size whenever shmem_huge_global_enabled() returns non-zero. While this works fine for the normal THP-enabled case as explained by Baolin in [1], this has two problems: 1. Theoretically, when shmem is configured for within_size, this could set blksize to PMD size even though the allocation may be a smaller mTHP order 2. A future commit will allow shmem THP support to be enabled even when the CPU doesn't support PMD-sized pages. We should not allow blksize to be set to PMD size in this case In order to fix #1 and prepare for #2, this commit sets blksize to the size of the highest supported order returned by shmem_huge_global_enabled(). [1] https://lore.kernel.org/linux-mm/6591a74c-7ef9-4614-9ae9-cb2fbed86ebf@linux.alibaba.com/ Suggested-by: Baolin Wang Acked-by: Zi Yan Signed-off-by: Luiz Capitulino --- mm/shmem.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/mm/shmem.c b/mm/shmem.c index eeb9a78c125a..b963f55640a8 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1506,6 +1506,7 @@ static int shmem_getattr(struct mnt_idmap *idmap, { struct inode *inode = path->dentry->d_inode; struct shmem_inode_info *info = SHMEM_I(inode); + unsigned int orders; /* Fast-path hint; recalc under info->lock corrects any stale read. */ if (data_race(info->alloced - info->swapped != inode->i_mapping->nrpages)) @@ -1522,8 +1523,9 @@ static int shmem_getattr(struct mnt_idmap *idmap, STATX_ATTR_NODUMP); generic_fillattr(idmap, request_mask, inode, stat); - if (shmem_huge_global_enabled(inode, 0, 0, false, NULL, 0)) - stat->blksize = HPAGE_PMD_SIZE; + orders = shmem_huge_global_enabled(inode, 0, 0, false, NULL, 0); + if (orders) + stat->blksize = PAGE_SIZE << highest_order(orders); if (request_mask & STATX_BTIME) { stat->result_mask |= STATX_BTIME; -- 2.55.0