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 DEAE0C433EF for ; Wed, 6 Jul 2022 03:05:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230042AbiGFDFF (ORCPT ); Tue, 5 Jul 2022 23:05:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56202 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229582AbiGFDFE (ORCPT ); Tue, 5 Jul 2022 23:05:04 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6B2171AF15 for ; Tue, 5 Jul 2022 20:05:02 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.55]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4Ld49G50BNzcg10; Wed, 6 Jul 2022 11:02:58 +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; Wed, 6 Jul 2022 11:04:46 +0800 Subject: Re: [mm-unstable PATCH v4 1/9] mm/hugetlb: check gigantic_page_runtime_supported() in return_unused_surplus_pages() To: =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= CC: Naoya Horiguchi , "linux-mm@kvack.org" , Andrew Morton , David Hildenbrand , Mike Kravetz , 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> From: Miaohe Lin Message-ID: <185c2a5e-8987-c679-b522-418b5072f1bd@huawei.com> Date: Wed, 6 Jul 2022 11:04:46 +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: <20220705063918.GA2508809@hori.linux.bs1.fc.nec.co.jp> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit 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 2022/7/5 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. Thanks. > >> >> 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? > > If pool shrinking is always allowed, we need uptdate max_huge_pages so, > the above if-block should have "goto out;", but it will be removed anyway > so we don't have to care for it. > > Thank you for the valuable comment. > > - Naoya Horiguchi >