From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-111.freemail.mail.aliyun.com (out30-111.freemail.mail.aliyun.com [115.124.30.111]) (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 4C7BC2D8391 for ; Wed, 15 Apr 2026 09:04:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.111 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776243857; cv=none; b=MqWbqjuedU2YVTbiktkRww3fNtO62faEv0coZdFc+ibqKwL9m5QqiNaH2BaJpKufCweYQ+CcFtRVDmCnLGDKTHKPGaVDU2xM2pWXim6XWxsZfpnP3z1CfQXsSRS6Nk5SG++qHf+rmb1UW9wFbKai++7bQBJ5++IZ3VvASHC5eyY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776243857; c=relaxed/simple; bh=SEY9OQa75FEMOT0l3sGUNO+yyl/z6Qek7npiqcdqeBw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=j9swyD0lzICMwDrVWTfRdNMYtCYrT1ATGpynbqIYJHwzkvEAq5iV8RhunmqoJpwpQZZV+/yOQ2ACtxevCq2k477BHaVY1/dXYWM+KCbcRTu27teOjeVIN1wejXZ7hKAUNJnMkOw0MLcoJ9kHTeeplgIUoblTWNnlTlr1rqDUo9g= 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=UR3usZWN; arc=none smtp.client-ip=115.124.30.111 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="UR3usZWN" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1776243851; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=WZXCR3v/1e2hz4wXUuiewvZGR4/jMr34Rcd+pZEUtH0=; b=UR3usZWNaX7XSItQyyHx8cucRuF3f0BhiWAfhfwcFo5vySPLUvH4013YkTUXMrXldV6f8poIv3bqIBoEhA95lG5+to28Kw/bF+y2qAJ49Td+uC3ldaA7w/KYXU0Tk/ScLlJsjDbGCiGblAMY3/fecVc8p1nwE23/pAf/wYM/j4w= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R331e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033045098064;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=9;SR=0;TI=SMTPD_---0X1448p5_1776243849; Received: from 30.74.144.121(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0X1448p5_1776243849 cluster:ay36) by smtp.aliyun-inc.com; Wed, 15 Apr 2026 17:04:10 +0800 Message-ID: Date: Wed, 15 Apr 2026 17:04:09 +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: "David Hildenbrand (Arm)" , akpm@linux-foundation.org, hughd@google.com Cc: willy@infradead.org, ziy@nvidia.com, ljs@kernel.org, lance.yang@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 4/15/26 4:47 PM, David Hildenbrand (Arm) wrote: > On 4/15/26 10:22, Baolin Wang wrote: >> Anonymous shmem large order allocations are dynamically controlled via the >> global THP sysfs knob (/sys/kernel/mm/transparent_hugepage/shmem_enabled) >> and the per-size mTHP knobs (/sys/kernel/mm/transparent_hugepage/hugepages-kB/shmem_enabled). >> >> Therefore, anonymous shmem uses shmem_allowable_huge_orders() to check >> which large orders are allowed, rather than relying on mapping_max_folio_order(). >> Moreover, mapping_max_folio_order() is intended to control large order >> allocations only for tmpfs mounts. Clarify this by not setting a large-order >> range for internal shmem mount (e.g. anonymous shmem), to avoid confusion, >> as discussed in the previous thread[1]. >> >> [1] https://lore.kernel.org/all/ec927492-4577-4192-8fad-85eb1bb43121@linux.alibaba.com/ >> Signed-off-by: Baolin Wang >> --- >> Changes from v1: >> - Update the comments and commit message, per Lance. >> --- >> mm/shmem.c | 12 ++++++++++-- >> 1 file changed, 10 insertions(+), 2 deletions(-) >> >> diff --git a/mm/shmem.c b/mm/shmem.c >> index 4ecefe02881d..568e1baee90d 100644 >> --- a/mm/shmem.c >> +++ b/mm/shmem.c >> @@ -3088,8 +3088,16 @@ static struct inode *__shmem_get_inode(struct mnt_idmap *idmap, >> if (sbinfo->noswap) >> mapping_set_unevictable(inode->i_mapping); >> >> - /* Don't consider 'deny' for emergencies and 'force' for testing */ >> - if (sbinfo->huge) >> + /* >> + * Only set the large order range for tmpfs mounts. The large order >> + * selection for the internal shmem mount is configured dynamically >> + * via the 'shmem_enabled' interfaces, so there is no need to set a >> + * large order range for the internal shmem mount's mapping. >> + * >> + * Note: Don't consider 'deny' for emergencies and 'force' for >> + * testing. >> + */ >> + if (sbinfo->huge && !(sb->s_flags & SB_KERNMOUNT)) >> mapping_set_large_folios(inode->i_mapping); > > I don't like that special casing. In an ideal world, any mapping that > supports large folios would indicate that. > > Now, which large folios to allocate is a different question. > > What's the problem with indicating for all shmem mappings that support > large folios that support, but handling *which* folio sizes to allocate > elsewhere? Thanks for taking a look. As I mentioned, the original logic has several issues for anonymous shmem: 1. Whether anonymous shmem supports large folios can be dynamically configured via sysfs interfaces, so mapping_set_large_folios() set during initialization cannot accurately reflect whether anonymous shmem actually supports large folios. 2. Calling mapping_set_large_folios() here by default makes anonymous shmem support 'MAX_PAGECACHE_ORDER' by default. However, the range of large orders supported by anonymous shmem is also dynamically configurable via sysfs interfaces, which could cause more confusion. 3. Currently, no users will call mapping_large_folio_support() related functions to determine whether large folios are supported for anonymous shmem. Therefore, rather than having anonymous shmem call mapping_set_large_folios() and introduce so much confusion, I'd prefer to exclude anonymous shmem from calling mapping_set_large_folios().