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 AC8FF32ED24 for ; Fri, 2 Oct 2026 19:11:33 +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=1790968295; cv=none; b=S+8qsPQMotz5jFVH83/+sS7oqilIcqmluMknWCCQl5dP3Xj8Mj2WxU5qqlZmfbWX7mmhEZ/TF/9V5mrlE04sqWb+BcWKaFLRK59oJR4VUpPyIPnuXIr58jUxNFvam/+FSZElwOhkv4hT6ALQoWzEoNhZ608eGgTnQTU2SFzx2hg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790968295; c=relaxed/simple; bh=ucAm/2QLfZNdrttee+pgFwfEQOBs8O/voze0AdcSsbo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=jBbtFm9+JjjkMKKIBzWPZFdAwncUVpbddysrKvjME8AycbJDidHbOzdPG2DWtPRQKjTsrdxQCa4Ur2O5ITl4ScoMnYLRV4zXoE9f3td4rO7ijeoHmsw1xBObDVrV5PEnJIZHuZxI5Tn3VPE0omc2sF6VAYrTi0jVOkog+OEhYtI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=C2uZjQ51; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="C2uZjQ51" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D7A3C1F000FF; Fri, 2 Oct 2026 19:11:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790968293; bh=xepjiv98niKg0eR0g6TZAWyusgKSgcyQj0ds3O6lxl8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=C2uZjQ51Jdphz8xDCTe/fSF/32tpFJFx0vjUDSdoaiHb0qAbb0G2b1bfsryrQ/Pn/ 5jXtmI4fD6jGmsStgw/UIWAxCkX52RITB/QLhfy7swkp5kOgud/qG8Ve5IWaxAud8Q Ed81tCq6BrT4/7U/DbRBZ/3EWbhPvYs3jMI6wbCepIJwkDeV3y0IaYk79XGWKkLrS0 e4uniPe5HIIEGt3kotlBlzO5mPWV5uc8ESf0vnV2hUAEXLPNKLD15BfpaMF+kYajC4 fRVCHrxl3aQ7OW6OYUrdu11E1tdhOjhedYdvqHYS+OlV32z6DRR54aOGqKzljjItpt cby3qki4jXyiA== Message-ID: <7bd00f36-3f48-490e-ab4c-7ed15be931d2@kernel.org> Date: Fri, 2 Oct 2026 21:11:22 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 02/14] mm: shmem: shmem_getattr(): set blksize to highest supported THP order To: Luiz Capitulino , linux-kernel@vger.kernel.org, linux-mm@kvack.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 References: <0f18a45baec44d193f8dbc760ef57c0430e04bdb.1789695931.git.luizcap@redhat.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/18/26 03:45, Luiz Capitulino wrote: > 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 b572c60f2af8..776dff8a848e 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; Heh, looking into the history of this I stumble over commit 89fdcd262fd40712da65e922558872a12b203332 Author: Yang Shi Date: Thu Jun 7 17:06:59 2018 -0700 mm: shmem: make stat.st_blksize return huge page size if THP is on Since tmpfs THP was supported in 4.8, hugetlbfs is not the only filesystem with huge page support anymore. tmpfs can use huge page via THP when mounting by "huge=" mount option. Which is a good read, especially regarding Hugh's comments: " : Sorry, I have no enthusiasm for this patch; but do I feel strongly : enough to override you and everyone else to NAK it? No, I don't feel : that strongly, maybe st_blksize isn't worth arguing over. : : We did look at struct stat when designing huge tmpfs, to see if there : were any fields that should be adjusted for it; but concluded none. : Yes, it would sometimes be nice to have a quickly accessible indicator : for when tmpfs has been mounted huge (scanning /proc/mounts for options : can be tiresome, agreed); but since tmpfs tries to supply huge (or not) : pages transparently, no difference seemed right. " (I agree with Hugh, also I find it odd to indicate for THP something > PAGE_SIZE) Anyhow, that ship has sailed. Effectively, I think "stat->blksize" is not that relevant. But indeed, today it gives us the highest *possible* size we could see on that system. shmem_huge_global_enabled() does not seem to depend on any runtime toggles that could change, only on inode properties. So your change looks good to me. Acked-by: David Hildenbrand (Arm) -- Cheers, David