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 BDB61C433EF for ; Thu, 7 Jul 2022 02:59:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234728AbiGGC7f (ORCPT ); Wed, 6 Jul 2022 22:59:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59968 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234102AbiGGC7d (ORCPT ); Wed, 6 Jul 2022 22:59:33 -0400 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8A15B29822 for ; Wed, 6 Jul 2022 19:59:32 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.57]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4Ldh001dXtz1L8y9; Thu, 7 Jul 2022 10:57:04 +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; Thu, 7 Jul 2022 10:59:29 +0800 Subject: Re: [mm-unstable PATCH v4 1/9] mm/hugetlb: check gigantic_page_runtime_supported() in return_unused_surplus_pages() To: Mike Kravetz , CC: =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= , Naoya Horiguchi , "linux-mm@kvack.org" , Andrew Morton , David Hildenbrand , Liu Shixin , Yang Shi , Oscar Salvador , Muchun Song , "linux-kernel@vger.kernel.org" References: <20220704013312.2415700-1-naoya.horiguchi@linux.dev> <20220704013312.2415700-2-naoya.horiguchi@linux.dev> <865207df-b272-c7c9-e90c-5748262d3d87@huawei.com> <20220705063918.GA2508809@hori.linux.bs1.fc.nec.co.jp> <185c2a5e-8987-c679-b522-418b5072f1bd@huawei.com> From: Miaohe Lin Message-ID: Date: Thu, 7 Jul 2022 10:59:29 +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: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) 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 2022/7/6 11:22, Mike Kravetz wrote: > On 07/06/22 11:04, Miaohe Lin wrote: >> On 2022/7/5 14:39, HORIGUCHI NAOYA(堀口 直也) wrote: >>> On Tue, Jul 05, 2022 at 10:16:39AM +0800, Miaohe Lin wrote: >>>> On 2022/7/4 9:33, Naoya Horiguchi wrote: >>>>> From: Naoya Horiguchi >>>>> >>>>> I found a weird state of 1GB hugepage pool, caused by the following >>>>> procedure: >>>>> >>>>> - run a process reserving all free 1GB hugepages, >>>>> - shrink free 1GB hugepage pool to zero (i.e. writing 0 to >>>>> /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages), then >>>>> - kill the reserving process. >>>>> >>>>> , then all the hugepages are free *and* surplus at the same time. >>>>> >>>>> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages >>>>> 3 >>>>> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/free_hugepages >>>>> 3 >>>>> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/resv_hugepages >>>>> 0 >>>>> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/surplus_hugepages >>>>> 3 >>>>> >>>>> This state is resolved by reserving and allocating the pages then >>>>> freeing them again, so this seems not to result in serious problem. >>>>> But it's a little surprising (shrinking pool suddenly fails). >>>>> >>>>> This behavior is caused by hstate_is_gigantic() check in >>>>> return_unused_surplus_pages(). This was introduced so long ago in 2008 >>>>> by commit aa888a74977a ("hugetlb: support larger than MAX_ORDER"), and >>>>> at that time the gigantic pages were not supposed to be allocated/freed >>>>> at run-time. Now kernel can support runtime allocation/free, so let's >>>>> check gigantic_page_runtime_supported() together. >>>>> >>>>> Signed-off-by: Naoya Horiguchi >>>> >>>> This patch looks good to me with a few question below. >>> >>> Thank you for reviewing. >>> >>>> >>>>> --- >>>>> v2 -> v3: >>>>> - Fixed typo in patch description, >>>>> - add !gigantic_page_runtime_supported() check instead of removing >>>>> hstate_is_gigantic() check (suggested by Miaohe and Muchun) >>>>> - add a few more !gigantic_page_runtime_supported() check in >>>>> set_max_huge_pages() (by Mike). >>>>> --- >>>>> mm/hugetlb.c | 19 ++++++++++++++++--- >>>>> 1 file changed, 16 insertions(+), 3 deletions(-) >>>>> >>>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >>>>> index 2a554f006255..bdc4499f324b 100644 >>>>> --- a/mm/hugetlb.c >>>>> +++ b/mm/hugetlb.c >>>>> @@ -2432,8 +2432,7 @@ static void return_unused_surplus_pages(struct hstate *h, >>>>> /* Uncommit the reservation */ >>>>> h->resv_huge_pages -= unused_resv_pages; >>>>> >>>>> - /* Cannot return gigantic pages currently */ >>>>> - if (hstate_is_gigantic(h)) >>>>> + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) >>>>> goto out; >>>>> >>>>> /* >>>>> @@ -3315,7 +3314,8 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid, >>>>> * the user tries to allocate gigantic pages but let the user free the >>>>> * boottime allocated gigantic pages. >>>>> */ >>>>> - if (hstate_is_gigantic(h) && !IS_ENABLED(CONFIG_CONTIG_ALLOC)) { >>>>> + if (hstate_is_gigantic(h) && (!IS_ENABLED(CONFIG_CONTIG_ALLOC) || >>>>> + !gigantic_page_runtime_supported())) { >>>>> if (count > persistent_huge_pages(h)) { >>>>> spin_unlock_irq(&hugetlb_lock); >>>>> mutex_unlock(&h->resize_lock); >>>>> @@ -3363,6 +3363,19 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid, >>>>> goto out; >>>>> } >>>>> >>>>> + /* >>>>> + * We can not decrease gigantic pool size if runtime modification >>>>> + * is not supported. >>>>> + */ >>>>> + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) { >>>>> + if (count < persistent_huge_pages(h)) { >>>>> + spin_unlock_irq(&hugetlb_lock); >>>>> + mutex_unlock(&h->resize_lock); >>>>> + NODEMASK_FREE(node_alloc_noretry); >>>>> + return -EINVAL; >>>>> + } >>>>> + } >>>> >>>> With above change, we're not allowed to decrease the pool size now. But it was allowed previously >>>> even if !gigantic_page_runtime_supported. Does this will break user? >>> >>> Yes, it does. I might get the wrong idea about the definition of >>> gigantic_page_runtime_supported(), which shows that runtime pool *extension* >>> is supported or not (implying that pool shrinking is always possible). >>> If this is right, this new if-block is not necessary. >> >> I tend to remove above new if-block to keep pool shrinking available. >> > > Not sure I am following the questions. > > Take a look at __update_and_free_page which will refuse to 'free' a > gigantic page if !gigantic_page_runtime_supported. I 'think' attempting > to shrink the pool when !gigantic_page_runtime_supported will result in > leaking gigantic pages. i.e. Memory will remain allocated for the It seems the commit 4eb0716e868e ("hugetlb: allow to free gigantic pages regardless of the configuration") adds the ability to free gigantic pages even if !gigantic_page_supported(). If the gigantic pages can't be freed due to gigantic_page_runtime_supported check if __update_and_free_page, there might be something need to do -- disallow trying to free gigantic pages when !gigantic_page_supported or succeeds to free gigantic pages regardless of gigantic_page_supported. Maybe I am missing something important. Add Alexandre to help confirm. Thanks! > gigantic page, but it can not be used. > > I can take a closer look during my tomorrow. > > IIRC, the only way gigantic_page_runtime_supported is not set to day is > in the case of powerpc using 16GB pages allocated/managed by firmware. >