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Wed, 11 Nov 2020 00:47:17 +0000 Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1]) by aserp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 0AB0Uqti171386; Wed, 11 Nov 2020 00:47:17 GMT Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by aserp3020.oracle.com with ESMTP id 34p5g12s9n-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 11 Nov 2020 00:47:16 +0000 Received: from abhmp0020.oracle.com (abhmp0020.oracle.com [141.146.116.26]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 0AB0l6Su031556; Wed, 11 Nov 2020 00:47:07 GMT Received: from [192.168.2.112] (/50.38.35.18) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 10 Nov 2020 16:47:05 -0800 Subject: Re: [PATCH v3 05/21] mm/hugetlb: Introduce pgtable allocation/freeing helpers To: Muchun Song , 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, osalvador@suse.de, mhocko@suse.com Cc: duanxiongchun@bytedance.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org References: <20201108141113.65450-1-songmuchun@bytedance.com> <20201108141113.65450-6-songmuchun@bytedance.com> From: Mike Kravetz Message-ID: <9dc62874-379f-b126-94a7-5bd477529407@oracle.com> Date: Tue, 10 Nov 2020 16:47:03 -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: <20201108141113.65450-6-songmuchun@bytedance.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9801 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxscore=0 spamscore=0 malwarescore=0 adultscore=0 phishscore=0 bulkscore=0 mlxlogscore=999 suspectscore=2 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011110001 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9801 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 lowpriorityscore=0 priorityscore=1501 clxscore=1015 malwarescore=0 mlxscore=0 spamscore=0 suspectscore=2 mlxlogscore=999 impostorscore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011110001 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 11/8/20 6:10 AM, Muchun Song wrote: > On x86_64, vmemmap is always PMD mapped if the machine has hugepages > support and if we have 2MB contiguos pages and PMD aligned. If we want > to free the unused vmemmap pages, we have to split the huge pmd firstly. > So we should pre-allocate pgtable to split PMD to PTE. > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index a0007902fafb..5c7be2ee7e15 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -1303,6 +1303,108 @@ static inline void destroy_compound_gigantic_page(struct page *page, ... > +static inline void vmemmap_pgtable_init(struct page *page) > +{ > + page_huge_pte(page) = NULL; > +} > + > +static void vmemmap_pgtable_deposit(struct page *page, pgtable_t pgtable) > +{ > + /* FIFO */ > + if (!page_huge_pte(page)) > + INIT_LIST_HEAD(&pgtable->lru); > + else > + list_add(&pgtable->lru, &page_huge_pte(page)->lru); > + page_huge_pte(page) = pgtable; > +} > + > +static pgtable_t vmemmap_pgtable_withdraw(struct page *page) > +{ > + pgtable_t pgtable; > + > + /* FIFO */ > + pgtable = page_huge_pte(page); > + page_huge_pte(page) = list_first_entry_or_null(&pgtable->lru, > + struct page, lru); > + if (page_huge_pte(page)) > + list_del(&pgtable->lru); > + return pgtable; > +} > + > +static int vmemmap_pgtable_prealloc(struct hstate *h, struct page *page) > +{ > + int i; > + pgtable_t pgtable; > + unsigned int nr = pgtable_pages_to_prealloc_per_hpage(h); > + > + if (!nr) > + return 0; > + > + vmemmap_pgtable_init(page); > + > + for (i = 0; i < nr; i++) { > + pte_t *pte_p; > + > + pte_p = pte_alloc_one_kernel(&init_mm); > + if (!pte_p) > + goto out; > + vmemmap_pgtable_deposit(page, virt_to_page(pte_p)); > + } > + > + return 0; > +out: > + while (i-- && (pgtable = vmemmap_pgtable_withdraw(page))) > + pte_free_kernel(&init_mm, page_to_virt(pgtable)); > + return -ENOMEM; > +} > + > +static void vmemmap_pgtable_free(struct hstate *h, struct page *page) > +{ > + pgtable_t pgtable; > + unsigned int nr = pgtable_pages_to_prealloc_per_hpage(h); > + > + if (!nr) > + return; > + > + pgtable = page_huge_pte(page); > + if (!pgtable) > + return; > + > + while (nr-- && (pgtable = vmemmap_pgtable_withdraw(page))) > + pte_free_kernel(&init_mm, page_to_virt(pgtable)); > +} I may be confused. In patch 9 of this series, the first call to vmemmap_pgtable_free() is made: > @@ -1645,6 +1799,10 @@ void free_huge_page(struct page *page) > > static void prep_new_huge_page(struct hstate *h, struct page *page, int nid) > { > + free_huge_page_vmemmap(h, page); > + /* Must be called before the initialization of @page->lru */ > + vmemmap_pgtable_free(h, page); > + > INIT_LIST_HEAD(&page->lru); > set_compound_page_dtor(page, HUGETLB_PAGE_DTOR); > set_hugetlb_cgroup(page, NULL); When I saw that comment in previous patch series, I assumed page->lru was being used to store preallocated pages and pages to free. However, unless I am reading the code incorrectly it does not appear page->lru (of the huge page) is being used for this purpose. Is that correct? If it is correct, would using page->lru of the huge page make this code simpler? I am just missing the reason why you are using page_huge_pte(page)->lru -- Mike Kravetz