From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qg0-f44.google.com (mail-qg0-f44.google.com [209.85.192.44]) by kanga.kvack.org (Postfix) with ESMTP id EB46382FA6 for ; Fri, 2 Oct 2015 16:53:17 -0400 (EDT) Received: by qgev79 with SMTP id v79so105243190qge.0 for ; Fri, 02 Oct 2015 13:53:17 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id j16si11959844qge.10.2015.10.02.13.53.17 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 02 Oct 2015 13:53:17 -0700 (PDT) Date: Fri, 2 Oct 2015 13:53:15 -0700 From: Andrew Morton Subject: Re: [PATCH] mm: optimize PageHighMem() check Message-Id: <20151002135315.7ae22edce0bf54e38f69b1b0@linux-foundation.org> In-Reply-To: <560E2F29.5070807@synopsys.com> References: <1443513260-14598-1-git-send-email-vgupta@synopsys.com> <20151001162528.32c5338efdff2bdea838befd@linux-foundation.org> <560E2F29.5070807@synopsys.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: Vineet Gupta Cc: linux-mm@kvack.org, Naoya Horiguchi , Hugh Dickins , "Kirill A. Shutemov" , Michal Hocko , Jennifer Herbert , Konstantin Khlebnikov , linux-kernel@vger.kernel.org On Fri, 2 Oct 2015 12:45:53 +0530 Vineet Gupta wrote: > On Friday 02 October 2015 04:55 AM, Andrew Morton wrote: > > On Tue, 29 Sep 2015 13:24:20 +0530 Vineet Gupta wrote: > > > >> > This came up when implementing HIHGMEM/PAE40 for ARC. > >> > The kmap() / kmap_atomic() generated code seemed needlessly bloated due > >> > to the way PageHighMem() macro is implemented. > >> > It derives the exact zone for page and then does pointer subtraction > >> > with first zone to infer the zone_type. > >> > The pointer arithmatic in turn generates the code bloat. > >> > > >> > PageHighMem(page) > >> > is_highmem(page_zone(page)) > >> > zone_off = (char *)zone - (char *)zone->zone_pgdat->node_zones > >> > > >> > Instead use is_highmem_idx() to work on zone_type available in page flags > >> > > >> > ----- Before ----- > >> > 80756348: mov_s r13,r0 > >> > 8075634a: ld_s r2,[r13,0] > >> > 8075634c: lsr_s r2,r2,30 > >> > 8075634e: mpy r2,r2,0x2a4 > >> > 80756352: add_s r2,r2,0x80aef880 > >> > 80756358: ld_s r3,[r2,28] > >> > 8075635a: sub_s r2,r2,r3 > >> > 8075635c: breq r2,0x2a4,80756378 > >> > 80756364: breq r2,0x548,80756378 > >> > > >> > ----- After ----- > >> > 80756330: mov_s r13,r0 > >> > 80756332: ld_s r2,[r13,0] > >> > 80756334: lsr_s r2,r2,30 > >> > 80756336: sub_s r2,r2,1 > >> > 80756338: brlo r2,2,80756348 > >> > > >> > For x86 defconfig build (32 bit only) it saves around 900 bytes. > >> > For ARC defconfig with HIGHMEM, it saved around 2K bytes. > >> > > >> > ---->8------- > >> > ./scripts/bloat-o-meter x86/vmlinux-defconfig-pre x86/vmlinux-defconfig-post > >> > add/remove: 0/0 grow/shrink: 0/36 up/down: 0/-934 (-934) > >> > function old new delta > >> > saveable_page 162 154 -8 > >> > saveable_highmem_page 154 146 -8 > >> > skb_gro_reset_offset 147 131 -16 > >> > ... > >> > ... > >> > __change_page_attr_set_clr 1715 1678 -37 > >> > setup_data_read 434 394 -40 > >> > mon_bin_event 1967 1927 -40 > >> > swsusp_save 1148 1105 -43 > >> > _set_pages_array 549 493 -56 > >> > ---->8------- > >> > > >> > e.g. For ARC kmap() > >> > > > is_highmem() is deranged. Can't we use a bit in zone->flags or > > something? > > It won't be "a" bit since zone_type is an enum. Yes it will! static inline int is_highmem(struct zone *zone) { return test_bit(ZONE_HIGHMEM, &zone->flags); } > ... > > However this patch still is independent of that since we have struct page as > starting point and zone_type is available from there directly w/o monkeying around > with any zone structs. yup. -- 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