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Wed, 18 Nov 2020 22:54:31 +0000 Received: from pps.filterd (aserp3030.oracle.com [127.0.0.1]) by aserp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 0AIMfel8052638; Wed, 18 Nov 2020 22:54:31 GMT Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by aserp3030.oracle.com with ESMTP id 34uspvd68x-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 18 Nov 2020 22:54:31 +0000 Received: from abhmp0015.oracle.com (abhmp0015.oracle.com [141.146.116.21]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 0AIMsRgd025515; Wed, 18 Nov 2020 22:54:28 GMT Received: from [192.168.2.112] (/50.38.35.18) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Wed, 18 Nov 2020 14:54:27 -0800 Subject: Re: [PATCH v4 04/21] mm/hugetlb: Introduce nr_free_vmemmap_pages in the struct hstate To: Oscar Salvador , Muchun Song Cc: corbet@lwn.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, paulmck@kernel.org, mchehab+huawei@kernel.org, pawan.kumar.gupta@linux.intel.com, rdunlap@infradead.org, oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de, almasrymina@google.com, rientjes@google.com, willy@infradead.org, mhocko@suse.com, duanxiongchun@bytedance.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org References: <20201113105952.11638-1-songmuchun@bytedance.com> <20201113105952.11638-5-songmuchun@bytedance.com> <20201116133310.GA32129@linux> From: Mike Kravetz Message-ID: Date: Wed, 18 Nov 2020 14:54:25 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20201116133310.GA32129@linux> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9809 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 malwarescore=0 mlxscore=0 bulkscore=0 suspectscore=2 adultscore=0 spamscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011180156 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9809 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 bulkscore=0 clxscore=1015 malwarescore=0 impostorscore=0 lowpriorityscore=0 priorityscore=1501 mlxlogscore=999 adultscore=0 phishscore=0 suspectscore=2 spamscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011180157 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 11/16/20 5:33 AM, Oscar Salvador wrote: > On Fri, Nov 13, 2020 at 06:59:35PM +0800, Muchun Song wrote: >> +void __init hugetlb_vmemmap_init(struct hstate *h) >> +{ >> + unsigned int order = huge_page_order(h); >> + unsigned int vmemmap_pages; >> + >> + vmemmap_pages = ((1 << order) * sizeof(struct page)) >> PAGE_SHIFT; >> + /* >> + * The head page and the first tail page are not to be freed to buddy >> + * system, the others page will map to the first tail page. So there > "the remaining pages" might be more clear. > >> + * are (@vmemmap_pages - RESERVE_VMEMMAP_NR) pages can be freed. > "that can be freed" > >> + * >> + * Could RESERVE_VMEMMAP_NR be greater than @vmemmap_pages? This is >> + * not expected to happen unless the system is corrupted. So on the >> + * safe side, it is only a safety net. >> + */ >> + if (likely(vmemmap_pages > RESERVE_VMEMMAP_NR)) >> + h->nr_free_vmemmap_pages = vmemmap_pages - RESERVE_VMEMMAP_NR; >> + else >> + h->nr_free_vmemmap_pages = 0; > > This made think of something. > Since struct hstate hstates is global, all the fields should be defined to 0. > So, the following assignments in hugetlb_add_hstate: > > h->nr_huge_pages = 0; > h->free_huge_pages = 0; > > should not be needed. > Actually, we do not initialize other values like resv_huge_pages > or surplus_huge_pages. > > If that is the case, the "else" could go. > > Mike? Correct. Those assignments have been in the code for a very long time. > The changes itself look good to me. > I think that putting all the vemmap stuff into hugetlb-vmemmap.* was > the right choice. Agree! -- Mike Kravetz