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 D143AC433F5 for ; Thu, 5 May 2022 08:02:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346189AbiEEIGP (ORCPT ); Thu, 5 May 2022 04:06:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38262 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346224AbiEEIGP (ORCPT ); Thu, 5 May 2022 04:06:15 -0400 Received: from mail-pl1-x633.google.com (mail-pl1-x633.google.com [IPv6:2607:f8b0:4864:20::633]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 33972338A4 for ; Thu, 5 May 2022 01:02:36 -0700 (PDT) Received: by mail-pl1-x633.google.com with SMTP id j14so3697919plx.3 for ; Thu, 05 May 2022 01:02:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20210112.gappssmtp.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=PShkJzVucYzHmTWOWA19iZ2R7/CUl/du8x+v8/m6eak=; b=rXiO+G2RVXc79XKg+DxGCyvWynPSvXSf5jHVcLN6vb8WTIXeDgIGVT9fXj2f7csWGP hgBzSRld+vHsk8GHK0BCXG0OTatp1gKjEN/+drDy44zoWmUKOJbZtYd3W32uXzIebLrJ LZLVxRpSkwc7TfRK/qKQLZos1PlfwEQv7hC14IxjPLY00C0+JbHSwcR6BettVHJLH8jJ 0mHVxHwTyPXk8yqvjcCLskCITBkRQo2vU1Yqpo+pSNugqCxyjcfn2cG1cFaVw4k5Or4v YKTDltG7pWJ99XQ9JeSowH8FY4RaAoyI2zSRNCxXgchnAnAp4beFlmJROU1f//FlC1bN 3tAw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=PShkJzVucYzHmTWOWA19iZ2R7/CUl/du8x+v8/m6eak=; b=PXJgLr+OqJqqHW8BhUOXOi4zKPJ9Nn8omGnon++EnYgBPigKGd0JXZmUBzyg1jDI2V zCrfSI+cG8CscZ5o3PGPeiRkmT3+DtwPf0DokoOeX42GMBVej9hqfF1LYSjayJB00eHn HZlnMdhn22sueWP9GjkvF1SC5dMB70CXPbXt2DKnBKEoPsHYQQ7uLiw93Y21+OHypaaq KNGFs1NjJ8hSTulpKxejyfX1MLNp8lZTs8HrB3mhVa6JtW84+TGRaBDYQ63PYMtjS8wA n1aMwmdkNvcXvOTdYGNJPBtAz1drRZUeVZIL18SGNjZ4gM4sLiui1U+6W8w0XZk1LFeD 6PYQ== X-Gm-Message-State: AOAM530v7kftNBa/S+dz+vWeuhNE9J8T/8/CByrWkJ/jZzzAmuoS2SLx anmkPh15N1P8sbj4zGv3NAzdVw== X-Google-Smtp-Source: ABdhPJzcmP/gFjk5XJNOBaDdYfBOx/5hGLiE7KzRJVfV8g6ITCklmhjuG/AU1KnZXR3qk8hUmvtw3g== X-Received: by 2002:a17:902:e494:b0:15a:4b81:1c16 with SMTP id i20-20020a170902e49400b0015a4b811c16mr26803407ple.10.1651737755636; Thu, 05 May 2022 01:02:35 -0700 (PDT) Received: from localhost ([139.177.225.234]) by smtp.gmail.com with ESMTPSA id p9-20020a170902a40900b0015e8d4eb2acsm793721plq.246.2022.05.05.01.02.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 May 2022 01:02:35 -0700 (PDT) Date: Thu, 5 May 2022 16:02:31 +0800 From: Muchun Song To: Mike Kravetz Cc: corbet@lwn.net, akpm@linux-foundation.org, mcgrof@kernel.org, keescook@chromium.org, yzaikin@google.com, osalvador@suse.de, david@redhat.com, masahiroy@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, duanxiongchun@bytedance.com, smuchun@gmail.com Subject: Re: [PATCH v9 4/4] mm: hugetlb_vmemmap: add hugetlb_optimize_vmemmap sysctl Message-ID: References: <20220429121816.37541-1-songmuchun@bytedance.com> <20220429121816.37541-5-songmuchun@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Wed, May 04, 2022 at 08:36:00PM -0700, Mike Kravetz wrote: > On 5/4/22 19:35, Muchun Song wrote: > > On Wed, May 04, 2022 at 03:12:39PM -0700, Mike Kravetz wrote: > >> On 4/29/22 05:18, Muchun Song wrote: > >>> +static void vmemmap_optimize_mode_switch(enum vmemmap_optimize_mode to) > >>> +{ > >>> + if (vmemmap_optimize_mode == to) > >>> + return; > >>> + > >>> + if (to == VMEMMAP_OPTIMIZE_OFF) > >>> + static_branch_dec(&hugetlb_optimize_vmemmap_key); > >>> + else > >>> + static_branch_inc(&hugetlb_optimize_vmemmap_key); > >>> + vmemmap_optimize_mode = to; > >>> +} > >>> + > >>> static int __init hugetlb_vmemmap_early_param(char *buf) > >>> { > >>> bool enable; > >>> + enum vmemmap_optimize_mode mode; > >>> > >>> if (kstrtobool(buf, &enable)) > >>> return -EINVAL; > >>> > >>> - if (enable) > >>> - static_branch_enable(&hugetlb_optimize_vmemmap_key); > >>> - else > >>> - static_branch_disable(&hugetlb_optimize_vmemmap_key); > >>> + mode = enable ? VMEMMAP_OPTIMIZE_ON : VMEMMAP_OPTIMIZE_OFF; > >>> + vmemmap_optimize_mode_switch(mode); > >>> > >>> return 0; > >>> } > >>> @@ -60,6 +80,8 @@ int hugetlb_vmemmap_alloc(struct hstate *h, struct page *head) > >>> vmemmap_end = vmemmap_addr + (vmemmap_pages << PAGE_SHIFT); > >>> vmemmap_reuse = vmemmap_addr - PAGE_SIZE; > >>> > >>> + VM_BUG_ON_PAGE(!vmemmap_pages, head); > >>> + > >>> /* > >>> * The pages which the vmemmap virtual address range [@vmemmap_addr, > >>> * @vmemmap_end) are mapped to are freed to the buddy allocator, and > >>> @@ -69,8 +91,10 @@ int hugetlb_vmemmap_alloc(struct hstate *h, struct page *head) > >>> */ > >>> ret = vmemmap_remap_alloc(vmemmap_addr, vmemmap_end, vmemmap_reuse, > >>> GFP_KERNEL | __GFP_NORETRY | __GFP_THISNODE); > >>> - if (!ret) > >>> + if (!ret) { > >>> ClearHPageVmemmapOptimized(head); > >>> + static_branch_dec(&hugetlb_optimize_vmemmap_key); > >>> + } > >>> > >>> return ret; > >>> } > >>> @@ -84,6 +108,8 @@ void hugetlb_vmemmap_free(struct hstate *h, struct page *head) > >>> if (!vmemmap_pages) > >>> return; > >>> > >>> + static_branch_inc(&hugetlb_optimize_vmemmap_key); > >> > >> Can you explain the reasoning behind doing the static_branch_inc here in free, > >> and static_branch_dec in alloc? > >> IIUC, they may not be absolutely necessary but you could use the count to > >> know how many optimized pages are in use? Or, I may just be missing > >> something. > >> > > > > Partly right. One 'count' is not enough. I have implemented this with similar > > approach in v6 [1]. Except the 'count', we also need a lock to do synchronization. > > However, both count and synchronization are included in static_key_inc/dec > > infrastructure. It is simpler to use static_key_inc/dec directly, right? > > > > [1] https://lore.kernel.org/all/20220330153745.20465-5-songmuchun@bytedance.com/ > > > > Sorry, but I am a little confused. > > vmemmap_optimize_mode_switch will static_key_inc to enable and static_key_dec > to disable. In addition each time we optimize (allocate) a hugetlb page after > enabling we will static_key_inc. > > Suppose we have 1 hugetlb page optimized. So static count == 2 IIUC. > The someone turns off optimization via sysctl. static count == 1 ??? Definitely right. > If we then add another hugetlb page via nr_hugepages it seems that it > would be optimized as static count == 1. Is that correct? Do we need I'm wrong. > to free all hugetlb pages with optimization before we can add new pages > without optimization? > My bad. I think the following code would fix this. Thanks for your review carefully. diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c index 5820a681a724..997e192aeed7 100644 --- a/mm/hugetlb_vmemmap.c +++ b/mm/hugetlb_vmemmap.c @@ -105,7 +105,7 @@ void hugetlb_vmemmap_free(struct hstate *h, struct page *head) unsigned long vmemmap_end, vmemmap_reuse, vmemmap_pages; vmemmap_pages = hugetlb_optimize_vmemmap_pages(h); - if (!vmemmap_pages) + if (!vmemmap_pages || READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF) return; static_branch_inc(&hugetlb_optimize_vmemmap_key);