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 CC19EC43334 for ; Tue, 5 Jul 2022 02:16:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234444AbiGECQo (ORCPT ); Mon, 4 Jul 2022 22:16:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46604 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230364AbiGECQn (ORCPT ); Mon, 4 Jul 2022 22:16:43 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 16F5512610 for ; Mon, 4 Jul 2022 19:16:42 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.53]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4LcR8027vfzkWgn; Tue, 5 Jul 2022 10:14:40 +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; Tue, 5 Jul 2022 10:16:39 +0800 Subject: Re: [mm-unstable PATCH v4 1/9] mm/hugetlb: check gigantic_page_runtime_supported() in return_unused_surplus_pages() To: Naoya Horiguchi , CC: Andrew Morton , David Hildenbrand , Mike Kravetz , Liu Shixin , Yang Shi , Oscar Salvador , Muchun Song , Naoya Horiguchi , References: <20220704013312.2415700-1-naoya.horiguchi@linux.dev> <20220704013312.2415700-2-naoya.horiguchi@linux.dev> From: Miaohe Lin Message-ID: <865207df-b272-c7c9-e90c-5748262d3d87@huawei.com> Date: Tue, 5 Jul 2022 10:16:39 +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: <20220704013312.2415700-2-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: 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 2022/7/4 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. > --- > 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? And it seems it's not allowed to adjust the max_huge_pages now if !gigantic_page_runtime_supported for gigantic huge page. Should we just return for such case as there should be nothing to do now? Or am I miss something? Thanks! > + > /* > * Decrease the pool size > * First return free pages to the buddy allocator (being careful >