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 X-Spam-Level: X-Spam-Status: No, score=-8.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D3051C5519F for ; Fri, 20 Nov 2020 08:53:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6F0E022253 for ; Fri, 20 Nov 2020 08:53:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=bytedance-com.20150623.gappssmtp.com header.i=@bytedance-com.20150623.gappssmtp.com header.b="N5BsUqRd" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725824AbgKTIwm (ORCPT ); Fri, 20 Nov 2020 03:52:42 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36246 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727061AbgKTIwm (ORCPT ); Fri, 20 Nov 2020 03:52:42 -0500 Received: from mail-pl1-x641.google.com (mail-pl1-x641.google.com [IPv6:2607:f8b0:4864:20::641]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6EE01C061A04 for ; Fri, 20 Nov 2020 00:52:42 -0800 (PST) Received: by mail-pl1-x641.google.com with SMTP id s2so4518764plr.9 for ; Fri, 20 Nov 2020 00:52:42 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=zpNptVEuWzTVs1t2YZA8V1BK1+nQ/xLKMvtlTpvsiNM=; b=N5BsUqRdrzvSw9AHWZZyrIIthOxBDzszxZllUK77vwE59ZQelnxtVCObH/ZZK2Vw7M rLy1RI+ru0XDHzycpGag2P2fSftv+XPBCzQf4DRTy40YMdKx93654iCy1prysMuHfnrd XJYFtOgP3E7SEuxIPL3Gctaltw7yGhhyMeSvyTefv19A3WDZcpbKBVLtR7parCS5NiLG uNpdTmc7TiRt7y3EW/ESytrDvqpv+7dJ2rV7MbLouSFomLdR7rbO1KDMDG3cJuJI3Sf3 skXK1rNeiKWVZZCSBhRQgDTJZW5EEN8yZ1bNVzie05HGjDQ4fZca2TSzpUU5ARswisw0 qvZQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=zpNptVEuWzTVs1t2YZA8V1BK1+nQ/xLKMvtlTpvsiNM=; b=e1Maf/8/nKBYZDC/y5/wY41QOmpqJT/W/uvf5qFDWK/m39Y2Hoi8ROdYqiEkY/MwW9 AvwROGkFeIuw8brLV4B6lFtkk1UlXRCaseakVnw/r+8useJ5HUjbMyIuXS02Rm0pJ4w3 AMC6r/esoingGNEJ4t4zu4ncGNM7vIe2J+9GGgQH+/Wtn6cHoA5XX+GNW+snsKhbvaPS 4XF0jTI5mNZIYniYV8pAjEiehfv9mLjWGYLEdS9hk8bhnmEnMx3xq3AQp4/gUF2zOECb Tukoo1GHjjP3e9ftc0UhS7UV5oe3jo3KpP8wE0JGHRVdQHvQvxLW5xWkoe0VK/RBk1Lr 0EjA== X-Gm-Message-State: AOAM533BLueDsBAYQz8g4yTOvQ3RzxfBQEYmSWiEg7FtPqWmWTENt9NK M/2AC+C1mw7Zd4r+7XkSU61aHpWPj734ejm8SH8kGg== X-Google-Smtp-Source: ABdhPJwlDBHCTerTRacGWw2itZ5Ez5TirD6WZf/c7BEGg462vAoZLIr8yw3+7RDjdDmEuv9EbGXEI9G5aPzAlqKWK8U= X-Received: by 2002:a17:902:76c8:b029:d9:d6c3:357d with SMTP id j8-20020a17090276c8b02900d9d6c3357dmr7764836plt.34.1605862361852; Fri, 20 Nov 2020 00:52:41 -0800 (PST) MIME-Version: 1.0 References: <20201120064325.34492-1-songmuchun@bytedance.com> <20201120064325.34492-12-songmuchun@bytedance.com> <20201120081123.GC3200@dhcp22.suse.cz> In-Reply-To: <20201120081123.GC3200@dhcp22.suse.cz> From: Muchun Song Date: Fri, 20 Nov 2020 16:51:59 +0800 Message-ID: Subject: Re: [External] Re: [PATCH v5 11/21] mm/hugetlb: Allocate the vmemmap pages associated with each hugetlb page To: Michal Hocko Cc: Jonathan Corbet , Mike Kravetz , Thomas Gleixner , mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, Peter Zijlstra , viro@zeniv.linux.org.uk, Andrew Morton , paulmck@kernel.org, mchehab+huawei@kernel.org, pawan.kumar.gupta@linux.intel.com, Randy Dunlap , oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de, Mina Almasry , David Rientjes , Matthew Wilcox , Oscar Salvador , "Song Bao Hua (Barry Song)" , Xiongchun duan , linux-doc@vger.kernel.org, LKML , Linux Memory Management List , linux-fsdevel Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Fri, Nov 20, 2020 at 4:11 PM Michal Hocko wrote: > > On Fri 20-11-20 14:43:15, Muchun Song wrote: > [...] > > diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c > > index eda7e3a0b67c..361c4174e222 100644 > > --- a/mm/hugetlb_vmemmap.c > > +++ b/mm/hugetlb_vmemmap.c > > @@ -117,6 +117,8 @@ > > #define RESERVE_VMEMMAP_NR 2U > > #define RESERVE_VMEMMAP_SIZE (RESERVE_VMEMMAP_NR << PAGE_SHIFT) > > #define TAIL_PAGE_REUSE -1 > > +#define GFP_VMEMMAP_PAGE \ > > + (GFP_KERNEL | __GFP_NOFAIL | __GFP_MEMALLOC) > > This is really dangerous! __GFP_MEMALLOC would allow a complete memory > depletion. I am not even sure triggering the OOM killer is a reasonable > behavior. It is just unexpected that shrinking a hugetlb pool can have > destructive side effects. I believe it would be more reasonable to > simply refuse to shrink the pool if we cannot free those pages up. This > sucks as well but it isn't destructive at least. I find the instructions of __GFP_MEMALLOC from the kernel doc. %__GFP_MEMALLOC allows access to all memory. This should only be used when the caller guarantees the allocation will allow more memory to be freed very shortly. Our situation is in line with the description above. We will free a HugeTLB page to the buddy allocator which is much larger than that we allocated shortly. Thanks. > -- > Michal Hocko > SUSE Labs -- Yours, Muchun