From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f49.google.com (mail-pa0-f49.google.com [209.85.220.49]) by kanga.kvack.org (Postfix) with ESMTP id 3326B6B0031 for ; Thu, 17 Apr 2014 19:00:43 -0400 (EDT) Received: by mail-pa0-f49.google.com with SMTP id lj1so846762pab.8 for ; Thu, 17 Apr 2014 16:00:42 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTP id py5si9266778pbc.400.2014.04.17.16.00.41 for ; Thu, 17 Apr 2014 16:00:42 -0700 (PDT) Date: Thu, 17 Apr 2014 16:00:39 -0700 From: Andrew Morton Subject: Re: [PATCH 5/5] hugetlb: add support for gigantic page allocation at runtime Message-Id: <20140417160039.28e031760e7546ee54c6fc7b@linux-foundation.org> In-Reply-To: <1397152725-20990-6-git-send-email-lcapitulino@redhat.com> References: <1397152725-20990-1-git-send-email-lcapitulino@redhat.com> <1397152725-20990-6-git-send-email-lcapitulino@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Luiz Capitulino Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, mtosatti@redhat.com, aarcange@redhat.com, mgorman@suse.de, andi@firstfloor.org, davidlohr@hp.com, rientjes@google.com, isimatu.yasuaki@jp.fujitsu.com, yinghai@kernel.org, riel@redhat.com, n-horiguchi@ah.jp.nec.com, kirill@shutemov.name On Thu, 10 Apr 2014 13:58:45 -0400 Luiz Capitulino wrote: > HugeTLB is limited to allocating hugepages whose size are less than > MAX_ORDER order. This is so because HugeTLB allocates hugepages via > the buddy allocator. Gigantic pages (that is, pages whose size is > greater than MAX_ORDER order) have to be allocated at boottime. > > However, boottime allocation has at least two serious problems. First, > it doesn't support NUMA and second, gigantic pages allocated at > boottime can't be freed. > > This commit solves both issues by adding support for allocating gigantic > pages during runtime. It works just like regular sized hugepages, > meaning that the interface in sysfs is the same, it supports NUMA, > and gigantic pages can be freed. > > For example, on x86_64 gigantic pages are 1GB big. To allocate two 1G > gigantic pages on node 1, one can do: > > # echo 2 > \ > /sys/devices/system/node/node1/hugepages/hugepages-1048576kB/nr_hugepages > > And to free them all: > > # echo 0 > \ > /sys/devices/system/node/node1/hugepages/hugepages-1048576kB/nr_hugepages > > The one problem with gigantic page allocation at runtime is that it > can't be serviced by the buddy allocator. To overcome that problem, this > commit scans all zones from a node looking for a large enough contiguous > region. When one is found, it's allocated by using CMA, that is, we call > alloc_contig_range() to do the actual allocation. For example, on x86_64 > we scan all zones looking for a 1GB contiguous region. When one is found, > it's allocated by alloc_contig_range(). > > One expected issue with that approach is that such gigantic contiguous > regions tend to vanish as runtime goes by. The best way to avoid this for > now is to make gigantic page allocations very early during system boot, say > from a init script. Other possible optimization include using compaction, > which is supported by CMA but is not explicitly used by this commit. Why aren't we using compaction? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org