From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-119.freemail.mail.aliyun.com (out30-119.freemail.mail.aliyun.com [115.124.30.119]) (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 0BF1B1643B for ; Thu, 16 Apr 2026 01:45:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.119 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776303954; cv=none; b=tVQ9nEawllRm276ZQlxHSUae3tTnrrCcGqYE1hfYiJy7cuQjHs/3HfhjPegnPVh3YBPzy+iUFWzUvFob3B7Uv/+u/zoYaYW0VOsXpC5JR5rGuRnEHKKMklpIzuTT0E9biwgOurUI6qSUcgfSYfrrQclxwmF9yuu7oL/xPAz2bC0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776303954; c=relaxed/simple; bh=IM6iRJMO0Z12axmyHXHLphMcTLJt5af169lgYPcyU/E=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=KI6AaeFlVkR2MYnUIc4KMvBvUSHPwxyjoUydwK5jCuu9OPdJFtzBgNZ6lAPeDOe+06UUl9cisTOZU/X9030g3Fm5KICrtUSRjBD+7hG0PAxWU60Ziwi74t3K1MgTt1HrteHRXAinSBO1d8Vx1o6ircZRBGrlEfp5yRlF0eULNO0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=Sy7XB+eO; arc=none smtp.client-ip=115.124.30.119 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="Sy7XB+eO" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1776303943; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=8h9cBCwBs64wq1vOrdidY69OFOjVelo1DpjFyEePV/M=; b=Sy7XB+eOHVnEzS2dlocJZjlymynwsyAnRFFu5oTuHGuC2TF/UEeDWQ7Th0na/Ul3HCxfrU3LPAi5DfIInWXDxYo4XVmmlG7ybWLKX5Qny8rzRyHs3D5EuWpl4M5Y+hT7oNpvTU0T22lLjrsrSPZyUmf4LXQJoa6dqfP6u4fgnTY= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R121e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033032089153;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=9;SR=0;TI=SMTPD_---0X16GbQ1_1776303942; Received: from 30.74.144.131(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0X16GbQ1_1776303942 cluster:ay36) by smtp.aliyun-inc.com; Thu, 16 Apr 2026 09:45:43 +0800 Message-ID: <907b3a20-52b3-4969-8456-bd3a8d2571f2@linux.alibaba.com> Date: Thu, 16 Apr 2026 09:45:42 +0800 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 v2] mm: shmem: don't set large-order range for internal shmem mount To: Zi Yan , "David Hildenbrand (Arm)" , willy@infradead.org Cc: akpm@linux-foundation.org, hughd@google.com, ljs@kernel.org, lance.yang@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <2d138a3f-0006-4a01-852a-4570d7ba781d@linux.alibaba.com> <1a3cb6b2-94e0-4268-8cd9-1f9a9deb6c6b@linux.alibaba.com> <875dc63b-0cd2-49e5-8b0d-3fb062789813@kernel.org> <846B17B0-1BAF-4959-8FC2-42744C44B1D6@nvidia.com> <16745f2b-b008-4df1-ac76-f18b4a826dbd@linux.alibaba.com> <4AD72E13-C4AE-4ADA-8AB2-DDB3CEE6A527@nvidia.com> From: Baolin Wang In-Reply-To: <4AD72E13-C4AE-4ADA-8AB2-DDB3CEE6A527@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 4/16/26 9:36 AM, Zi Yan wrote: > On 15 Apr 2026, at 21:22, Baolin Wang wrote: > >> On 4/16/26 9:11 AM, Zi Yan wrote: >>> On 15 Apr 2026, at 21:05, Baolin Wang wrote: >>> >>>> On 4/15/26 10:36 PM, David Hildenbrand (Arm) wrote: >>>>> On 4/15/26 12:05, Baolin Wang wrote: >>>>>> >>>>>> >>>>>> On 4/15/26 5:54 PM, David Hildenbrand (Arm) wrote: >>>>>>>> >>>>>>>> Yes, that makes sense. >>>>>>>> >>>>>>>> However, it’s also possible that the mapping does not support large >>>>>>>> folios, yet anonymous shmem can still allocate large folios via the >>>>>>>> sysfs interfaces. That doesn't make sense, right? >>>>>>> >>>>>>> That's what I am saying: if there could be large folios in there, then >>>>>>> let's tell the world. >>>>>>> >>>>>>> Getting in a scenario where the mapping claims to not support large >>>>>>> folios, but then we have large folios in there is inconsistent, not? >>>>>>> >>>>>>> [...] >>>>>>> >>>>>>>> >>>>>>>> For the current anonymous shmem (tmpfs is already clear, no questions), >>>>>>>> I don’t think there will be any "will never have/does never allow" >>>>>>>> cases, because it can be changed dynamically via the sysfs interfaces. >>>>>>> >>>>>>> Right. It's about non-anon shmem with huge=off. >>>>>>> >>>>>>>> >>>>>>>> If we still want that logic, then for anonymous shmem we can treat it as >>>>>>>> always "might have large folios". >>>>>> >>>>>> OK. To resolve the confusion about 1, the logic should be changed as >>>>>> follows. Does that make sense to you? >>>>>> >>>>>> if (sbinfo->huge || (sb->s_flags & SB_KERNMOUNT)) >>>>>>     mapping_set_large_folios(inode->i_mapping); >>>>> >>>>> I think that's better. >>>> >>>> Thanks for your valuable input. >>>> >>>> But has Willy says, maybe we can just >>>>> unconditionally set it and have it even simpler. >>>> >>>> However, for tmpfs mounts, we should still respect the 'huge=' mount option. See commit 5a90c155defa ("tmpfs: don't enable large folios if not supported"). >>> >>> Is it possible to get sbinfo->huge during tmpfs’s folio allocation time, so that >>> even if all tmpfs has mapping_set_large_folios() but sbinfo->huge can still >>> decide whether huge page will be allocated for a tmpfs? >> >> Yes, of course. However, the issue isn’t whether tmpfs allows allocating large folios. >> >> The problem commit 5a90c155defa tries to fix is that when tmpfs is mounted with the 'huge=never' option, we will not allocate large folios for it. Then when writing tmpfs files, generic_perform_write() will call mapping_max_folio_size() to get the chunk size and ends up with an order-9 size for writing tmpfs files. However, this tmpfs file is populated only with small folios, resulting in a performance regression. > > IIUC, generic_perform_write() needs to use a small chunk if tmpfs denies huge. > It seems that Kefeng did that in the first try[1]. But willy suggested > the current fix. > > I wonder if we should revisit Kefeng’s first version. > > [1] https://lore.kernel.org/all/20240914140613.2334139-1-wangkefeng.wang@huawei.com/ Personally, I still prefer the current fix (commit 5a90c155defa). We should honor the tmpfs mount option. If it explicitly says no large folios, we shouldn’t call mapping_set_large_folios(). Isn’t that more consistent with its semantics?