From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 11B7CC19759 for ; Thu, 1 Aug 2019 14:50:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D8CC620665 for ; Thu, 1 Aug 2019 14:50:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732280AbfHAOuf (ORCPT ); Thu, 1 Aug 2019 10:50:35 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53308 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731148AbfHAOuf (ORCPT ); Thu, 1 Aug 2019 10:50:35 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 2F8822D0FC7; Thu, 1 Aug 2019 14:50:35 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.136]) by smtp.corp.redhat.com (Postfix) with SMTP id 5531B5C207; Thu, 1 Aug 2019 14:50:33 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Thu, 1 Aug 2019 16:50:34 +0200 (CEST) Date: Thu, 1 Aug 2019 16:50:32 +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: <20190801145032.GB31538@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 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Thu, 01 Aug 2019 14:50:35 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/31, Song Liu wrote: > > +static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm, > + unsigned long addr) > +{ > + struct mm_slot *mm_slot; > + int ret = 0; > + > + /* hold mmap_sem for khugepaged_test_exit() */ > + VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm); > + VM_BUG_ON(addr & ~HPAGE_PMD_MASK); > + > + if (unlikely(khugepaged_test_exit(mm))) > + return 0; > + > + if (!test_bit(MMF_VM_HUGEPAGE, &mm->flags) && > + !test_bit(MMF_DISABLE_THP, &mm->flags)) { > + ret = __khugepaged_enter(mm); > + if (ret) > + return ret; > + } could you explain why do we need mm->mmap_sem, khugepaged_test_exit() check and __khugepaged_enter() ? > + spin_lock(&khugepaged_mm_lock); > + mm_slot = get_mm_slot(mm); > + if (likely(mm_slot && mm_slot->nr_pte_mapped_thp < MAX_PTE_MAPPED_THP)) > + mm_slot->pte_mapped_thp[mm_slot->nr_pte_mapped_thp++] = addr; if get_mm_slot() returns mm_slot != NULL we can safely modify ->pte_mapped_thp. We do not care even if this task has already passed __mmput/__khugepaged_exit, this slot can't go away. No? Oleg.