From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f175.google.com (mail-wi0-f175.google.com [209.85.212.175]) by kanga.kvack.org (Postfix) with ESMTP id EA8036B0070 for ; Tue, 22 Apr 2014 17:37:56 -0400 (EDT) Received: by mail-wi0-f175.google.com with SMTP id cc10so3994376wib.8 for ; Tue, 22 Apr 2014 14:37:56 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTP id iy13si5938958wic.55.2014.04.22.14.37.54 for ; Tue, 22 Apr 2014 14:37:55 -0700 (PDT) Date: Tue, 22 Apr 2014 17:37:26 -0400 From: Luiz Capitulino Subject: Re: [PATCH v3 0/5] hugetlb: add support gigantic page allocation at runtime Message-ID: <20140422173726.738d0635@redhat.com> In-Reply-To: <20140417160110.3f36b972b25525fbbe23681b@linux-foundation.org> References: <1397152725-20990-1-git-send-email-lcapitulino@redhat.com> <20140417160110.3f36b972b25525fbbe23681b@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton 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, 17 Apr 2014 16:01:10 -0700 Andrew Morton wrote: > On Thu, 10 Apr 2014 13:58:40 -0400 Luiz Capitulino wrote: > > > The HugeTLB subsystem uses the buddy allocator to allocate hugepages during > > runtime. This means that hugepages allocation during runtime is limited to > > MAX_ORDER order. For archs supporting gigantic pages (that is, page sizes > > greater than MAX_ORDER), this in turn means that those pages can't be > > allocated at runtime. > > Dumb question: what's wrong with just increasing MAX_ORDER? To be honest I'm not a buddy allocator expert and I'm not familiar with what is involved in increasing MAX_ORDER. What I do know though is that it's not just a matter of increasing a macro's value. For example, for sparsemem support we have this check (include/linux/mmzone.h:1084): #if (MAX_ORDER - 1 + PAGE_SHIFT) > SECTION_SIZE_BITS #error Allocator MAX_ORDER exceeds SECTION_SIZE #endif I _guess_ it's because we can't allocate more pages than what's within a section on sparsemem. Can sparsemem and the other stuff be changed to accommodate a bigger MAX_ORDER? I don't know. Is it worth it to increase MAX_ORDER and do all the required changes, given that a bigger MAX_ORDER is only useful for HugeTLB and the archs supporting gigantic pages? I'd guess not. -- 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