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 AD454C71153 for ; Tue, 29 Aug 2023 03:34:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235583AbjH2DeG (ORCPT ); Mon, 28 Aug 2023 23:34:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59440 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235390AbjH2Ddo (ORCPT ); Mon, 28 Aug 2023 23:33:44 -0400 Received: from out-248.mta0.migadu.com (out-248.mta0.migadu.com [91.218.175.248]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4DC7011C for ; Mon, 28 Aug 2023 20:33:41 -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=1693280017; 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=TbU8Li2pRJ88mITWQeQKv1yZgPCpNOVQ4jVcRFDLRV8=; b=lsH6FSk/Ob/4Bz2BuQiJvTRRTAxO/IJpT9k/r9eGA4q/ZzUHku6pCOkbDNOd3SVMbHc4Ns Ml6suvzSu9UZYuWXilXUnFtVloKwgC5kvh/DCDpTGffbqj2Nfc5yzuLRUUaS5MpScxu9+h TGSl9WcY/IuPR1GBdyO5zgzz9laDDVs= Mime-Version: 1.0 Subject: Re: [v3 4/4] mm: hugetlb: Skip initialization of gigantic tail struct pages if freed by HVO X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Muchun Song In-Reply-To: <20230828210418.GD3290@monkey> Date: Tue, 29 Aug 2023 11:33:10 +0800 Cc: Usama Arif , Linux-MM , Mike Rapoport , LKML , Muchun Song , fam.zheng@bytedance.com, liangma@liangbit.com, punit.agrawal@bytedance.com Content-Transfer-Encoding: quoted-printable Message-Id: References: <20230825111836.1715308-1-usama.arif@bytedance.com> <20230825111836.1715308-5-usama.arif@bytedance.com> <486CFF93-3BB1-44CD-B0A0-A47F560F2CAE@linux.dev> <20230828210418.GD3290@monkey> To: Mike Kravetz X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Aug 29, 2023, at 05:04, Mike Kravetz = wrote: >=20 > On 08/28/23 19:33, Muchun Song wrote: >>=20 >>=20 >>> On Aug 25, 2023, at 19:18, Usama Arif = wrote: >>>=20 >>> The new boot flow when it comes to initialization of gigantic pages >>> is as follows: >>> - At boot time, for a gigantic page during __alloc_bootmem_hugepage, >>> the region after the first struct page is marked as noinit. >>> - This results in only the first struct page to be >>> initialized in reserve_bootmem_region. As the tail struct pages are >>> not initialized at this point, there can be a significant saving >>> in boot time if HVO succeeds later on. >>> - Later on in the boot, HVO is attempted. If its successful, only = the first >>> HUGETLB_VMEMMAP_RESERVE_SIZE / sizeof(struct page) - 1 tail struct = pages >>> after the head struct page are initialized. If it is not successful, >>> then all of the tail struct pages are initialized. >>>=20 >>> Signed-off-by: Usama Arif >>=20 >> This edition is simpler than before ever, thanks for your work. >>=20 >> There is premise that other subsystems do not access vmemmap pages >> before the initialization of vmemmap pages associated withe HugeTLB >> pages allocated from bootmem for your optimization. However, IIUC, = the >> compacting path could access arbitrary struct page when memory fails >> to be allocated via buddy allocator. So we should make sure that >> those struct pages are not referenced in this routine. And I know >> if CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled, it will encounter >> the same issue, but I don't find any code to prevent this from >> happening. I need more time to confirm this, if someone already = knows, >> please let me know, thanks. So I think HugeTLB should adopt the = similar >> way to prevent this. >=20 > In this patch, the call to hugetlb_vmemmap_optimize() is moved BEFORE > __prep_new_hugetlb_folio or prep_new_hugetlb_folio in all code paths. > The prep_new_hugetlb_folio routine(s) are what set the destructor = (soon > to be a flag) that identifies the set of pages as a hugetlb page. So, > there is now a window where a set of pages not identified as hugetlb > will not have vmemmap pages. Thanks for your point it out. Seems this issue is not related to this change? = hugetlb_vmemmap_optimize() is called before the setting of destructor since the initial commit f41f2ed43ca5. Right? >=20 > Recently, I closed the same window in the hugetlb freeing code paths = with > commit 32c877191e02 'hugetlb: do not clear hugetlb dtor until = allocating'. Yes, I saw it.=20 > This patch needs to be reworked so that this window is not opened in = the > allocation paths. So I think the fix should be a separate series. Thanks.