From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-101.freemail.mail.aliyun.com (out30-101.freemail.mail.aliyun.com [115.124.30.101]) (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 DC72D1482F3 for ; Thu, 28 Nov 2024 07:41:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.101 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732779669; cv=none; b=G1PY/RwuWf8HzoiJei5Ba7oU36ijefuMGgklF+cAyQz3Xd0cCB3qZdJ/uKOKVdo3N+1OTkziipAHZs2yu+NwNRM6mQBk88sge4Ec8DUZn4xs7qozUwxEGhmwtYVVElNLnnEhJVyQ8e3o2QbRzPYbLiSiIa6cjTzMn8m0SlWSjzI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732779669; c=relaxed/simple; bh=1VTUoG2V0gyervSpFGg9a7iaCwc6rFfs5nzrk8u2P+U=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=EoclGHhq9BThDF7A/X4WILUX+3+YdsomI2SW9v8Y8b+PdkackN2ax4zkZotg47JejS1tAGnkZV3pAsGEzf+Dy3bTL8w1Yt6XnLHpmNKddPMjn8wSwiHeIX2nf/Z/REMy/L9fpTHI+yzbCjSnqq+qcv+cwXfRJgSu8tWZH8yq1nc= 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=aJpe0Hmg; arc=none smtp.client-ip=115.124.30.101 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="aJpe0Hmg" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1732779660; h=From:To:Subject:Date:Message-Id:MIME-Version; bh=4geB5O7mEfI/X7677yTwrrvC9HQS1VjRPAOpYyMK/zg=; b=aJpe0Hmg0o3VTImpuD6hAmY2tJNdzR4FocU5j+RovPSRXoJDhknGhgcBRlsvgFSc6u5i27C8sTopDd6mkSDV+ZhpumMfMnv1rqQYKev8MsC7JsaAVum044jpMxR+UgVsKNN9vfbwH+QHyZjlSdbGNTTkYc4/L4lNKpu5IklA2aI= Received: from localhost(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0WKOx1qd_1732779658 cluster:ay36) by smtp.aliyun-inc.com; Thu, 28 Nov 2024 15:40:59 +0800 From: Baolin Wang To: akpm@linux-foundation.org, hughd@google.com Cc: willy@infradead.org, david@redhat.com, wangkefeng.wang@huawei.com, 21cnbao@gmail.com, ryan.roberts@arm.com, ioworker0@gmail.com, da.gomez@samsung.com, baolin.wang@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v3 5/6] docs: tmpfs: update the large folios policy for tmpfs and shmem Date: Thu, 28 Nov 2024 15:40:43 +0800 Message-Id: <9b7418af30e300d1eb05721b81d79074d0bb0ec9.1732779148.git.baolin.wang@linux.alibaba.com> X-Mailer: git-send-email 2.39.3 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: David Hildenbrand Update the large folios policy for tmpfs and shmem. Signed-off-by: David Hildenbrand Signed-off-by: Baolin Wang --- Documentation/admin-guide/mm/transhuge.rst | 58 +++++++++++++++------- 1 file changed, 41 insertions(+), 17 deletions(-) diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst index 9ae775eaacbe..ba6edff728ed 100644 --- a/Documentation/admin-guide/mm/transhuge.rst +++ b/Documentation/admin-guide/mm/transhuge.rst @@ -358,8 +358,21 @@ default to ``never``. Hugepages in tmpfs/shmem ======================== -You can control hugepage allocation policy in tmpfs with mount option -``huge=``. It can have following values: +Traditionally, tmpfs only supported a single huge page size ("PMD"). Today, +it also supports smaller sizes just like anonymous memory, often referred +to as "multi-size THP" (mTHP). Huge pages of any size are commonly +represented in the kernel as "large folios". + +While there is fine control over the huge page sizes to use for the internal +shmem mount (see below), ordinary tmpfs mounts will make use of all available +huge page sizes without any control over the exact sizes, behaving more like +other file systems. + +tmpfs mounts +------------ + +The THP allocation policy for tmpfs mounts can be adjusted using the mount +option: ``huge=``. It can have following values: always Attempt to allocate huge pages every time we need a new page; @@ -374,19 +387,19 @@ within_size advise Only allocate huge pages if requested with fadvise()/madvise(); -The default policy is ``never``. +Remember, that the kernel may use huge pages of all available sizes, and +that no fine control as for the internal tmpfs mount is available. + +The default policy in the past was ``never``, but it can now be adjusted +using the kernel parameter ``transparent_hugepage_tmpfs=``. ``mount -o remount,huge= /mountpoint`` works fine after mount: remounting ``huge=never`` will not attempt to break up huge pages at all, just stop more from being allocated. -There's also sysfs knob to control hugepage allocation policy for internal -shmem mount: /sys/kernel/mm/transparent_hugepage/shmem_enabled. The mount -is used for SysV SHM, memfds, shared anonymous mmaps (of /dev/zero or -MAP_ANONYMOUS), GPU drivers' DRM objects, Ashmem. - -In addition to policies listed above, shmem_enabled allows two further -values: +In addition to policies listed above, the sysfs knob +/sys/kernel/mm/transparent_hugepage/shmem_enabled will affect the +allocation policy of tmpfs mounts, when set to the following values: deny For use in emergencies, to force the huge option off from @@ -394,13 +407,24 @@ deny force Force the huge option on for all - very useful for testing; -Shmem can also use "multi-size THP" (mTHP) by adding a new sysfs knob to -control mTHP allocation: -'/sys/kernel/mm/transparent_hugepage/hugepages-kB/shmem_enabled', -and its value for each mTHP is essentially consistent with the global -setting. An 'inherit' option is added to ensure compatibility with these -global settings. Conversely, the options 'force' and 'deny' are dropped, -which are rather testing artifacts from the old ages. +shmem / internal tmpfs +---------------------- +The mount internal tmpfs mount is used for SysV SHM, memfds, shared anonymous +mmaps (of /dev/zero or MAP_ANONYMOUS), GPU drivers' DRM objects, Ashmem. + +To control the THP allocation policy for this internal tmpfs mount, the +sysfs knob /sys/kernel/mm/transparent_hugepage/shmem_enabled and the knobs +per THP size in +'/sys/kernel/mm/transparent_hugepage/hugepages-kB/shmem_enabled' +can be used. + +The global knob has the same semantics as the ``huge=`` mount options +for tmpfs mounts, except that the different huge page sizes can be controlled +individually, and will only use the setting of the global knob when the +per-size knob is set to 'inherit'. + +The options 'force' and 'deny' are dropped for the individual sizes, which +are rather testing artifacts from the old ages. always Attempt to allocate huge pages every time we need a new page; -- 2.39.3