From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx124.postini.com [74.125.245.124]) by kanga.kvack.org (Postfix) with SMTP id E31D26B0087 for ; Mon, 25 Mar 2013 09:01:59 -0400 (EDT) From: "Kirill A. Shutemov" In-Reply-To: <514C6CE3.5080201@sr71.net> References: <1363283435-7666-1-git-send-email-kirill.shutemov@linux.intel.com> <1363283435-7666-5-git-send-email-kirill.shutemov@linux.intel.com> <514B2D94.8040206@sr71.net> <20130322094745.E20D9E0085@blue.fi.intel.com> <514C6CE3.5080201@sr71.net> Subject: Re: [PATCHv2, RFC 04/30] radix-tree: implement preload for multiple contiguous elements Content-Transfer-Encoding: 7bit Message-Id: <20130325130345.15B3AE0085@blue.fi.intel.com> Date: Mon, 25 Mar 2013 15:03:45 +0200 (EET) Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: "Kirill A. Shutemov" , Andrea Arcangeli , Andrew Morton , Al Viro , Hugh Dickins , Wu Fengguang , Jan Kara , Mel Gorman , linux-mm@kvack.org, Andi Kleen , Matthew Wilcox , "Kirill A. Shutemov" , Hillf Danton , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Dave Hansen wrote: > On 03/22/2013 02:47 AM, Kirill A. Shutemov wrote: > > Dave Hansen wrote: > >> On 03/14/2013 10:50 AM, Kirill A. Shutemov wrote: > >>> +#define RADIX_TREE_PRELOAD_NR 512 /* For THP's benefit */ > >> > >> This eventually boils down to making the radix_tree_preload array > >> larger. Do we really want to do this unconditionally if it's only for > >> THP's benefit? > > > > It will be useful not only for THP. Batching can be useful to solve > > scalability issues. > > Still, it seems like something that little machines with no THP support > probably don't want to pay the cost for. Perhaps you could enable it > for THP||NR_CPUS>$FOO. Okay, I'll disable it for !THP. We always can change it if we'll find good candidate for batching. > >> For those of us too lazy to go compile a kernel and figure this out in > >> practice, how much bigger does this make the nodes[] array? > > > > We have three possible RADIX_TREE_MAP_SHIFT: > > > > #ifdef __KERNEL__ > > #define RADIX_TREE_MAP_SHIFT (CONFIG_BASE_SMALL ? 4 : 6) > > #else > > #define RADIX_TREE_MAP_SHIFT 3 /* For more stressful testing */ > > #endif > > > > On 64-bit system: > > For RADIX_TREE_MAP_SHIFT=3, old array size is 43, new is 107. > > For RADIX_TREE_MAP_SHIFT=4, old array size is 31, new is 63. > > For RADIX_TREE_MAP_SHIFT=6, old array size is 21, new is 30. > > > > On 32-bit system: > > For RADIX_TREE_MAP_SHIFT=3, old array size is 21, new is 84. > > For RADIX_TREE_MAP_SHIFT=4, old array size is 15, new is 46. > > For RADIX_TREE_MAP_SHIFT=6, old array size is 11, new is 19. > > > > On most machines we will have RADIX_TREE_MAP_SHIFT=6. > > Could you stick that in your patch description? Will do. > The total cost is "array size" * sizeof(void*) * NR_CPUS, right? Correct. -- Kirill A. Shutemov -- 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