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[209.132.183.28]) by mx.google.com with ESMTPS id k67si35431916qkf.157.2019.08.01.05.43.55 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 01 Aug 2019 05:43:55 -0700 (PDT) Received-SPF: pass (google.com: domain of oleg@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of oleg@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=oleg@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id B4DDD308FF23; Thu, 1 Aug 2019 12:43:54 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.136]) by smtp.corp.redhat.com (Postfix) with SMTP id DE9E960A9F; Thu, 1 Aug 2019 12:43:52 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Thu, 1 Aug 2019 14:43:54 +0200 (CEST) Date: Thu, 1 Aug 2019 14:43:52 +0200 From: Oleg Nesterov To: Song Liu Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, matthew.wilcox@oracle.com, kirill.shutemov@linux.intel.com, kernel-team@fb.com, william.kucharski@oracle.com, srikar@linux.vnet.ibm.com Subject: Re: [PATCH v2 1/2] khugepaged: enable collapse pmd for pte-mapped THP Message-ID: <20190801124351.GA31538@redhat.com> References: <20190731183331.2565608-1-songliubraving@fb.com> <20190731183331.2565608-2-songliubraving@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190731183331.2565608-2-songliubraving@fb.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.49]); Thu, 01 Aug 2019 12:43:54 +0000 (UTC) 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 07/31, Song Liu wrote: > > +void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long haddr) > +{ > + struct vm_area_struct *vma = find_vma(mm, haddr); > + pmd_t *pmd = mm_find_pmd(mm, haddr); > + struct page *hpage = NULL; > + unsigned long addr; > + spinlock_t *ptl; > + int count = 0; > + pmd_t _pmd; > + int i; > + > + VM_BUG_ON(haddr & ~HPAGE_PMD_MASK); > + > + if (!vma || !pmd || pmd_trans_huge(*pmd)) ^^^^^^^^^^^^^^^^^^^^ mm_find_pmd() returns NULL if pmd_trans_huge() > + /* step 1: check all mapped PTEs are to the right huge page */ > + for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) { > + pte_t *pte = pte_offset_map(pmd, addr); > + struct page *page; > + > + if (pte_none(*pte)) > + continue; > + > + page = vm_normal_page(vma, addr, *pte); > + > + if (!PageCompound(page)) > + return; > + > + if (!hpage) { > + hpage = compound_head(page); > + if (hpage->mapping != vma->vm_file->f_mapping) Hmm. But how can we know this is still the same vma ? If nothing else, why vma->vm_file can't be NULL? Say, a process unmaps this memory after khugepaged_add_pte_mapped_thp() was called, then it does mmap(haddr, MAP_PRIVATE|MAP_ANONYMOUS), then do_huge_pmd_anonymous_page() installs a huge page at the same address, then split_huge_pmd() is called by any reason. No?