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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: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 790F4A008B X-Stat-Signature: o6strxaeddg615sbsbima7fd45przcng X-Rspam-User: Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=bytedance-com.20210112.gappssmtp.com header.s=20210112 header.b=rXiO+G2R; spf=pass (imf15.hostedemail.com: domain of songmuchun@bytedance.com designates 209.85.216.51 as permitted sender) smtp.mailfrom=songmuchun@bytedance.com; dmarc=pass (policy=none) header.from=bytedance.com X-HE-Tag: 1651737748-307233 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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);