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Thu, 8 Aug 2024 16:10:28 GMT Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4942F20040; Thu, 8 Aug 2024 16:10:26 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 07EF920067; Thu, 8 Aug 2024 16:10:26 +0000 (GMT) Received: from li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com (unknown [9.155.204.135]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTPS; Thu, 8 Aug 2024 16:10:25 +0000 (GMT) Date: Thu, 8 Aug 2024 18:10:24 +0200 From: Alexander Gordeev To: Wei Yang Cc: gerald.schaefer@linux.ibm.com, hca@linux.ibm.com, rppt@kernel.org, akpm@linux-foundation.org, brauner@kernel.org, oleg@redhat.com, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, David Hildenbrand Subject: Re: [PATCH v6 1/3] mm/memblock: introduce a new helper memblock_estimated_nr_free_pages() Message-ID: References: <20240808001415.6298-1-richard.weiyang@gmail.com> <20240808142405.ttlcfkximywtde6i@master> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240808142405.ttlcfkximywtde6i@master> X-TM-AS-GCONF: 00 X-Proofpoint-GUID: I88Rgv0M3bv42Qfs8v2efCUYJ-hx4yuQ X-Proofpoint-ORIG-GUID: lyNApa4Ov3JeXE1Hu1WbH0xjvn8aptV0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1039,Hydra:6.0.680,FMLib:17.12.28.16 definitions=2024-08-08_16,2024-08-07_01,2024-05-17_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 mlxscore=0 priorityscore=1501 bulkscore=0 lowpriorityscore=0 malwarescore=0 suspectscore=0 mlxlogscore=862 spamscore=0 clxscore=1015 impostorscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2407110000 definitions=main-2408080114 X-Stat-Signature: 3wnbec9du4mdw9pppd6y4fiabrqhaghn X-Rspamd-Queue-Id: 6569F180034 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1723133444-229043 X-HE-Meta: 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 MOgTDUDu 0UfAt00SezMRNPDG7tYbT6ifi/bf+F+hSClCbky3uTGib+dHFsT4k8G1OIx8HJEWz6+x8QAwQiGSwgzl6hQwNjtiipyusocmlhJv6x1dNnJjw9B9MhdQWoy99QqMH2uJg2EKIJAq1E7s4aFwdtzFciqpq0DjKs16GGqXVwU7puY9kntHjRjbqyXVpYzKgueVFUvyPOAbAb6htAqPqKFV+JmomxekZb4N7HIkbo19XuqcP0uQ7drD8KJKbDCrqO1wcudX/omg8L/+XgZbLYeczUfdtrq39UMcEj8XSxzHXYPNfzm648Ys0Q/2k2m9Hg0qGaAgw X-Bogosity: Ham, tests=bogofilter, spamicity=0.000102, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Aug 08, 2024 at 02:24:05PM +0000, Wei Yang wrote: > >> + * An estimated number of free pages from memblock point of view. > >> + */ > >> +unsigned long __init memblock_estimated_nr_free_pages(void) > >> +{ > >> + return PHYS_PFN(memblock_phys_mem_size() - memblock_reserved_size()); > >> +} > > > >This could possibly be short on up to two pages due to lack of alignment. > >The current uses are okay, but since you make it generic it probably matters. > > > > I don't follow, would you mind giving more detail? memblock_estimated_nr_free_pages() returns number of pages, not bytes. Yet, both memblock_phys_mem_size() and memblock_reserved_size() return a value which is not aligned on PAGE_SIZE. Therefore, the result of PHYS_PFN() applied to the difference between the two functions might be short on one (two?) page(s). > >Also, the returned value is not an estimation. Meaning the function name > >is rather unfortunate AFAICT. > > From my point of view, this is an estimation for two reasons: > > * value from memblock_xxx is not page size aligned > * reserved memory maybe released during boot stage > > It is not that easy to get the exact number of free pages here. Do I miss > something? No, with this reasoning it makes sense to me. > -- > Wei Yang > Help you, Help me Thank you for the clarification!