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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 31ABCC433EF for ; Sat, 25 Jun 2022 09:42:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232363AbiFYJmZ (ORCPT ); Sat, 25 Jun 2022 05:42:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42770 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231768AbiFYJmX (ORCPT ); Sat, 25 Jun 2022 05:42:23 -0400 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 382F336148 for ; Sat, 25 Jun 2022 02:42:22 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.53]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4LVTXQ3Ym2zDsSD; Sat, 25 Jun 2022 17:41:42 +0800 (CST) Received: from [10.174.177.76] (10.174.177.76) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Sat, 25 Jun 2022 17:42:18 +0800 Subject: Re: [PATCH v2 3/9] mm/hugetlb: make pud_huge() and huge_pud() aware of non-present pud entry To: Naoya Horiguchi CC: Andrew Morton , David Hildenbrand , Mike Kravetz , Liu Shixin , Yang Shi , Oscar Salvador , Muchun Song , Naoya Horiguchi , , Linux-MM References: <20220623235153.2623702-1-naoya.horiguchi@linux.dev> <20220623235153.2623702-4-naoya.horiguchi@linux.dev> From: Miaohe Lin Message-ID: <098b5a5c-2c05-4e22-b1ba-81f858391cd6@huawei.com> Date: Sat, 25 Jun 2022 17:42:17 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20220623235153.2623702-4-naoya.horiguchi@linux.dev> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/6/24 7:51, Naoya Horiguchi wrote: > From: Naoya Horiguchi > > follow_pud_mask() does not support non-present pud entry now. As long as > I tested on x86_64 server, follow_pud_mask() still simply returns > no_page_table() for non-present_pud_entry() due to pud_bad(), so no severe > user-visible effect should happen. But generally we should call > follow_huge_pud() for non-present pud entry for 1GB hugetlb page. > > Update pud_huge() and huge_pud() to handle non-present pud entries. The > changes are similar to previous works for pud entries commit e66f17ff7177 > ("mm/hugetlb: take page table lock in follow_huge_pmd()") and commit > cbef8478bee5 ("mm/hugetlb: pmd_huge() returns true for non-present hugepage"). > > Signed-off-by: Naoya Horiguchi > --- > arch/x86/mm/hugetlbpage.c | 3 ++- > mm/hugetlb.c | 26 +++++++++++++++++++++++++- > 2 files changed, 27 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c > index a0d023cb4292..5fb86fb49ba8 100644 > --- a/arch/x86/mm/hugetlbpage.c > +++ b/arch/x86/mm/hugetlbpage.c > @@ -70,7 +70,8 @@ int pmd_huge(pmd_t pmd) > No strong opinion but a comment similar to pmd_huge might be better? /* * pmd_huge() returns 1 if @pmd is hugetlb related entry, that is normal * hugetlb entry or non-present (migration or hwpoisoned) hugetlb entry. * Otherwise, returns 0. */ > int pud_huge(pud_t pud) > { > - return !!(pud_val(pud) & _PAGE_PSE); > + return !pud_none(pud) && > + (pud_val(pud) & (_PAGE_PRESENT|_PAGE_PSE)) != _PAGE_PRESENT; > } > #endif > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index f59f43c06601..b7ae5f73f3b2 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -6946,10 +6946,34 @@ struct page * __weak > follow_huge_pud(struct mm_struct *mm, unsigned long address, > pud_t *pud, int flags) > { > + struct page *page = NULL; > + spinlock_t *ptl; > + pte_t pte; > + > if (flags & (FOLL_GET | FOLL_PIN)) > return NULL; Should the above check be modified? It seems the below try_grab_page might not grab the page as expected (as Mike pointed out). Or the extra page refcnt is unneeded? > > - return pte_page(*(pte_t *)pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT); > +retry: > + ptl = huge_pte_lock(hstate_sizelog(PUD_SHIFT), mm, (pte_t *)pud); > + if (!pud_huge(*pud)) > + goto out; > + pte = huge_ptep_get((pte_t *)pud); > + if (pte_present(pte)) { > + page = pud_page(*pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT); > + if (WARN_ON_ONCE(!try_grab_page(page, flags))) { > + page = NULL; > + goto out; > + } > + } else { > + if (is_hugetlb_entry_migration(pte)) { > + spin_unlock(ptl); > + __migration_entry_wait(mm, (pte_t *)pud, ptl); > + goto retry; > + } Again. No strong opinion but a comment similar to follow_huge_pmd might be better? /* * hwpoisoned entry is treated as no_page_table in * follow_page_mask(). */ Thanks! > + } > +out: > + spin_unlock(ptl); > + return page; > } > > struct page * __weak >