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 D017EEE14C3 for ; Thu, 7 Sep 2023 03:34:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232432AbjIGDeH (ORCPT ); Wed, 6 Sep 2023 23:34:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52850 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229782AbjIGDeF (ORCPT ); Wed, 6 Sep 2023 23:34:05 -0400 Received: from out-218.mta1.migadu.com (out-218.mta1.migadu.com [IPv6:2001:41d0:203:375::da]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 99F7E1998 for ; Wed, 6 Sep 2023 20:34:01 -0700 (PDT) Content-Type: text/plain; charset=us-ascii DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1694057639; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=jhW4OFUYeYRsLujjWh8342NpTRqCb5qwMPST593N+Iw=; b=aFoKOlEEH0sST0kn8dxBc0tsmYKz+BnvyyHmV4ygebRCBEnCQL5+3u+WZIl9rcaMYtGyZj tyFreW/Fuo9S3b4n8OJMHOzHICpMRqqN6uj+usWWIDK9KigDtQqMjvpj2ApGkkiDHWyZKK dvkHNUtcfzH/LtcBDTAfTx93QYLEnQ0= Mime-Version: 1.0 Subject: Re: [PATCH v2 07/11] hugetlb: perform vmemmap restoration on a list of pages X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Muchun Song In-Reply-To: <20230906211234.GC3612@monkey> Date: Thu, 7 Sep 2023 11:33:18 +0800 Cc: Linux-MM , LKML , Muchun Song , Joao Martins , Oscar Salvador , David Hildenbrand , Miaohe Lin , David Rientjes , Anshuman Khandual , Naoya Horiguchi , Barry Song , Michal Hocko , Matthew Wilcox , Xiongchun Duan , Andrew Morton Content-Transfer-Encoding: quoted-printable Message-Id: References: <20230905214412.89152-1-mike.kravetz@oracle.com> <20230905214412.89152-8-mike.kravetz@oracle.com> <5e091211-9a32-8480-55fb-faff6a0fadef@linux.dev> <38E2F051-E00B-4104-A616-0EEB2729386F@linux.dev> <20230906211234.GC3612@monkey> To: Mike Kravetz X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Sep 7, 2023, at 05:12, Mike Kravetz = wrote: >=20 > On 09/06/23 16:07, Muchun Song wrote: >>> On Sep 6, 2023, at 15:33, Muchun Song wrote: >>> On 2023/9/6 05:44, Mike Kravetz wrote: >>>> When removing hugetlb pages from the pool, we first create a list >>>> of removed pages and then free those pages back to low level = allocators. >>>> Part of the 'freeing process' is to restore vmemmap for all base = pages >>>> if necessary. Pass this list of pages to a new routine >>>> hugetlb_vmemmap_restore_folios() so that vmemmap restoration can be >>>> performed in bulk. >>>>=20 >>>> Signed-off-by: Mike Kravetz >>>> --- >>>> mm/hugetlb.c | 3 +++ >>>> mm/hugetlb_vmemmap.c | 13 +++++++++++++ >>>> mm/hugetlb_vmemmap.h | 5 +++++ >>>> 3 files changed, 21 insertions(+) >>>>=20 >>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >>>> index 554be94b07bd..dd2dbc256172 100644 >>>> --- a/mm/hugetlb.c >>>> +++ b/mm/hugetlb.c >>>> @@ -1838,6 +1838,9 @@ static void update_and_free_pages_bulk(struct = hstate *h, struct list_head *list) >>>> { >>>> struct folio *folio, *t_folio; >>>> + /* First restore vmemmap for all pages on list. */ >>>> + hugetlb_vmemmap_restore_folios(h, list); >>>> + >>>> list_for_each_entry_safe(folio, t_folio, list, lru) { >>>> update_and_free_hugetlb_folio(h, folio, false); >>>> cond_resched(); >>>> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c >>>> index ac5577d372fe..79de984919ef 100644 >>>> --- a/mm/hugetlb_vmemmap.c >>>> +++ b/mm/hugetlb_vmemmap.c >>>> @@ -481,6 +481,19 @@ int hugetlb_vmemmap_restore(const struct = hstate *h, struct page *head) >>>> return ret; >>>> } >>>> +/* >>>> + * This function will attempt to resore vmemmap for a list of = folios. There >>>> + * is no guarantee that restoration will be successful for all or = any folios. >>>> + * This is used in bulk operations, and no feedback is given to = the caller. >>>> + */ >>>> +void hugetlb_vmemmap_restore_folios(const struct hstate *h, struct = list_head *folio_list) >>>> +{ >>>> + struct folio *folio; >>>> + >>>> + list_for_each_entry(folio, folio_list, lru) >>>> + (void)hugetlb_vmemmap_restore(h, &folio->page); >>>=20 >>> I am curious about the purpose of "void" here, seems it it not = necessnary, >>> ritgh? We cound see so many palces where we do not add the void if = the caller >>> does not care about the return value of the callee. >>=20 >> Another question: should we stop restoring vmemmap pages when >> hugetlb_vmemmap_restore() fails? In which case, I suspect there >> is no memory probably, there is no need to continue, right? >=20 > Recall that the list of hugetlb pages may be from multiple nodes. My = first > thought was that we should continue because memory allocation may fail = on one > node but succeed on another. However, with > = https://lore.kernel.org/linux-mm/20230905031312.91929-1-yuancan@huawei.com= / > memory allocation should fall back to other nodes. So, yes I do = believe it > would make sense to stop when hugetlb_vmemmap_restore returns ENOMEM = as > we are unlikely to make forward progress. Agree. >=20 > Today's behavior will try to restore vmemmap for all pages. No = stopping > on error. >=20 > I have mixed thoughts on this. Quitting on error 'seems reasonable'. > However, if we continue we 'might' be able to allocate vmemmap for one > hugetlb page. And, if we free one hugetlb page that should provide > vmemmap for several more and we may be able to free most pages on the > list. Yes. A good point. But there should be a non-optimized huge page been freed somewhere in parallel, otherwise we still cannot allocate memory. However, the freeing operation happens after = hugetlb_vmemmap_restore_folios. If we want to handle this, we should rework update_and_free_pages_bulk() to do a try when at least a huge pages is freed. Thanks. > --=20 > Mike Kravetz