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Shutemov" , Zi Yan , Michal Hocko , Huang Ying , Hugh Dickins , hca@linux.ibm.com, gor@linux.ibm.com, borntraeger@de.ibm.com, Andrew Morton , Linux MM , linux-s390@vger.kernel.org, Linux Kernel Mailing List , Alexander Gordeev Subject: Re: [RFC PATCH 0/6] mm: thp: use generic THP migration for NUMA hinting fault Message-ID: <20210406140251.2779c400@thinkpad> In-Reply-To: References: <20210329183312.178266-1-shy828301@gmail.com> <20210330164200.01a4b78f@thinkpad> <20210331134727.47bc1e6d@thinkpad> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: q_zihSF78QLKrq41D9xh6d-N3kDj0peG X-Proofpoint-GUID: vq66MAHLKvi_HZbyGR0D4zY8xfe448cU X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.369,18.0.761 definitions=2021-04-06_02:2021-04-01,2021-04-06 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 priorityscore=1501 adultscore=0 suspectscore=0 spamscore=0 phishscore=0 mlxlogscore=863 impostorscore=0 lowpriorityscore=0 bulkscore=0 malwarescore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104030000 definitions=main-2104060080 X-Rspamd-Queue-Id: DE947A0003A5 X-Stat-Signature: se4qcfc18qd3xcwx78rojbt3bq1wz9jt X-Rspamd-Server: rspam02 Received-SPF: none (linux.ibm.com>: No applicable sender policy available) receiver=imf15; identity=mailfrom; envelope-from=""; helo=mx0a-001b2d01.pphosted.com; client-ip=148.163.158.5 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617710581-799389 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: On Thu, 1 Apr 2021 13:10:49 -0700 Yang Shi wrote: [...] > > > > > > Yes, it could be. The old behavior of migration was to return -ENOMEM > > > if THP migration is not supported then split THP. That behavior was > > > not very friendly to some usecases, for example, memory policy and > > > migration lieu of reclaim (the upcoming). But I don't mean we restore > > > the old behavior. We could split THP if it returns -ENOSYS and the > > > page is THP. > > > > OK, as long as we don't get any broken PMD migration entries established > > for s390, some extra THP splitting would be acceptable I guess. > > There will be no migration PMD installed. The current behavior is a > no-op if THP migration is not supported. Ok, just for completeness, since Mel also replied that the split was not done on other architectures "because the loss from splitting exceeded the gain of improved locality": I did not mean to request extra splitting functionality for s390, simply skipping / ignoring large PMDs would also be fine for s390, no need to add extra complexity.