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Tue, 21 Sep 2021 13:52:49 +0000 (GMT) X-Mailer: emacs 28.0.50 (via feedmail 11-beta-1 I) From: "Aneesh Kumar K.V" To: Mike Kravetz , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: David Hildenbrand , Michal Hocko , Oscar Salvador , Zi Yan , Muchun Song , Naoya Horiguchi , David Rientjes , Andrew Morton , Mike Kravetz Subject: Re: [PATCH 5/8] hugetlb: document the demote sysfs interfaces In-Reply-To: <20210816224953.157796-6-mike.kravetz@oracle.com> References: <20210816224953.157796-1-mike.kravetz@oracle.com> <20210816224953.157796-6-mike.kravetz@oracle.com> Date: Tue, 21 Sep 2021 19:22:47 +0530 Message-ID: <87bl4m9gsw.fsf@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 0k0bnVnbB0LS0_TUvr9DncwHIw4HtLCL X-Proofpoint-ORIG-GUID: LaEMchr76khInJAkdHFxfn6RVNsPRWY5 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.182.1,Aquarius:18.0.790,Hydra:6.0.391,FMLib:17.0.607.475 definitions=2021-09-21_01,2021-09-20_01,2020-04-07_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 phishscore=0 priorityscore=1501 mlxscore=0 lowpriorityscore=0 malwarescore=0 impostorscore=0 adultscore=0 mlxlogscore=999 clxscore=1011 bulkscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2109030001 definitions=main-2109210083 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 7D1C1B0000B3 Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=ibm.com header.s=pp1 header.b=OX47MZyf; dmarc=pass (policy=none) header.from=ibm.com; spf=pass (imf19.hostedemail.com: domain of aneesh.kumar@linux.ibm.com designates 148.163.158.5 as permitted sender) smtp.mailfrom=aneesh.kumar@linux.ibm.com X-Stat-Signature: w67epifa8saddi4inynsmq7gtcn4ekce X-HE-Tag: 1632232378-898206 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Mike Kravetz writes: > Describe demote and demote_size interfaces. > > Signed-off-by: Mike Kravetz > --- > Documentation/admin-guide/mm/hugetlbpage.rst | 29 ++++++++++++++++++-- > 1 file changed, 27 insertions(+), 2 deletions(-) > > diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst > index 8abaeb144e44..902059a0257b 100644 > --- a/Documentation/admin-guide/mm/hugetlbpage.rst > +++ b/Documentation/admin-guide/mm/hugetlbpage.rst > @@ -234,8 +234,12 @@ will exist, of the form:: > > hugepages-${size}kB > > -Inside each of these directories, the same set of files will exist:: > +Inside each of these directories, the set of files contained in ``/proc`` > +will exist. In addition, two additional interfaces for demoting huge > +pages will exist:: > > + demote > + demote_size > nr_hugepages > nr_hugepages_mempolicy > nr_overcommit_hugepages > @@ -243,7 +247,28 @@ Inside each of these directories, the same set of files will exist:: > resv_hugepages > surplus_hugepages > > -which function as described above for the default huge page-sized case. > +The demote interfaces provide the ability to split a huge page into > +smaller huge pages. For example, the x86 architecture supports both > +1GB and 2MB huge pages sizes. A 1GB huge page can be split into 512 > +2MB huge pages. The demote interfaces are: > + > +demote_size > + is the size of demoted pages. When a page is demoted a corresponding > + number of huge pages of demote_size will be created. For huge pages > + of the smallest supported size (2MB on x86), demote_size will be the > + system page size (PAGE_SIZE). If demote_size is the system page size > + then demoting a page will simply free the huge page. demote_size is > + a read only interface. That is an alternate interface for nr_hugepages. Will it be better to return EINVAL on write to 'demote' file below /sys/kernel/mm/hugepages/hugepages-2048kB ? Or may be not expose demote possibility within 2M hugepage directory at all? > + > +demote > + is used to demote a number of huge pages. A user with root privileges > + can write to this file. It may not be possible to demote the > + requested number of huge pages. To determine how many pages were > + actually demoted, compare the value of nr_hugepages before and after > + writing to the demote interface. demote is a write only interface. > + > +The interfaces which are the same as in ``/proc`` function as described > +above for the default huge page-sized case. > > .. _mem_policy_and_hp_alloc: > > -- > 2.31.1