From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-186.mta1.migadu.com (out-186.mta1.migadu.com [95.215.58.186]) (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 0776A40DFD6 for ; Thu, 7 May 2026 03:30:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.186 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778124651; cv=none; b=CmQz0JdJfkQQpDw/ByYtdj6k4wDrI3MeI9eCfBFtj26WL9K4fP2mGkefnL7P2cnKTApLt/yQmaIv2NfoC3wTSmBoRZHAF12nWGpx/DKFGl1nO+NjjNAULl2AJ3feiLljSgmaNPIz1NA8roym6PK9pkW4HJXlsZQN9Rveb4lrvec= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778124651; c=relaxed/simple; bh=jqKPQiXpW98oldrpDjDj8FIZFTLmhrpfzebJ9KHHGwI=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=NWFcUaSnItlV5wMRDhBDqdF7KL1d44BEQ+SyODAr+8/u70or18cChKV4akQtrMiUbhylupzSaTW3KC4Dfbx0Ep5DfLB7fyTWW++2js+8vER3ZOK+bMVXf1qcCvA6aczReNwk/YciW7l39aKOiARPhtMNLXg+SbvrX68GRJa2f0U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=wKNe1+eN; arc=none smtp.client-ip=95.215.58.186 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="wKNe1+eN" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1778124646; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=gyZVzRsxXhQaw+/BT2qurWH8p+SNTVYpiB+XsnLougQ=; b=wKNe1+eNgeqPd05y2iLWXfahEWECb2xBV6LFtMbhJ/SgQmjH9tQEUCZeFHpSXAQKhrRJOp Azr0VuQ3gyPGc04emwvgd4V9ks6rWAWm5Z/ewD5QSMupmexgbMlVW5cYJy3E1Q/wRixsWK 2D2oc9njborSjMOUdqtqKxJWTK4j0aA= From: Lance Yang To: npache@redhat.com, ziy@nvidia.com Cc: akpm@linux-foundation.org, david@kernel.org, willy@infradead.org, songliubraving@fb.com, clm@fb.com, dsterba@suse.com, viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz, ljs@kernel.org, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, shuah@kernel.org, linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v5 01/14] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check Date: Thu, 7 May 2026 11:29:56 +0800 Message-Id: <20260507032956.51667-1-lance.yang@linux.dev> In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On Sun, May 03, 2026 at 09:48:40PM -0600, Nico Pache wrote: > > >On 4/29/26 9:29 AM, Zi Yan wrote: >> collapse_file() requires FSes supporting large folio with at least >> PMD_ORDER, so replace the READ_ONLY_THP_FOR_FS check with that. >> MADV_COLLAPSE ignores shmem huge config, so exclude the check for shmem. >> >> While at it, replace VM_BUG_ON with VM_WARN_ON_ONCE. >> >> Add a helper function mapping_pmd_folio_support() for FSes supporting large >> folio with at least PMD_ORDER. >> >> Signed-off-by: Zi Yan >> Reviewed-by: Lance Yang >> Reviewed-by: Baolin Wang >> --- >> include/linux/pagemap.h | 26 ++++++++++++++++++++++++++ >> mm/khugepaged.c | 10 ++++++++-- >> 2 files changed, 34 insertions(+), 2 deletions(-) >> >> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h >> index 1f50991b43e3b..1fed3414fe9b8 100644 >> --- a/include/linux/pagemap.h >> +++ b/include/linux/pagemap.h >> @@ -513,6 +513,32 @@ static inline bool mapping_large_folio_support(const struct address_space *mappi >> return mapping_max_folio_order(mapping) > 0; >> } >> >> +/** >> + * mapping_pmd_folio_support() - Check if a mapping support PMD-sized folio >> + * @mapping: The address_space >> + * >> + * Some file supports large folio but does not support as large as PMD order. >> + * If a PMD-sized pagecache folio is attempted to be created on a filesystem, >> + * this check needs to be performed first. >> + * >> + * Return: true - PMD-sized folio is supported, false - PMD-sized folio is not >> + * supported. >> + */ >> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE >> +static inline bool mapping_pmd_folio_support(const struct address_space *mapping) >> +{ >> + /* AS_FOLIO_ORDER is only reasonable for pagecache folios */ >> + VM_WARN_ON_ONCE((unsigned long)mapping & FOLIO_MAPPING_ANON); >> + >> + return mapping_max_folio_order(mapping) >= PMD_ORDER; > >Probably a stupid question, but I dont know FS thats well. > >Here we are checking that the max allowed folio order is greater than >(or eq) to the PMD_ORDER. Yet the function asks if PMD specifically is >supported. In the future could we have some FS that does not support PMD >orders, but does support larger orders (eg. PUD)? Good point. IIUC, mapping_max_folio_order() means "maximum supported order" not "the only supported order", so mapping_pmd_folio_support() just means "PMD order is within the supported range". Also, mapping_set_large_folios() sets the range to: mapping_set_folio_order_range(mapping, 0, MAX_PAGECACHE_ORDER); and __filemap_get_folio_mpol() treats max as a cap, then falls back down towards min. That said, if we want the helper name to mean "PMD order specifically is supported", the more future-proof test would be: mapping_min_folio_order(mapping) <= PMD_ORDER && mapping_max_folio_order(mapping) >= PMD_ORDER Thoughs?