On Friday 02 October 2015 04:55 AM, Andrew Morton wrote: > On Tue, 29 Sep 2015 13:24:20 +0530 Vineet Gupta <Vineet.Gupta1@xxxxxxxxxxxx> 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 <kmap+0x48> >> > 80756364: breq r2,0x548,80756378 <kmap+0x48> >> > >> > ----- 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 <kmap+0x30> >> > >> > 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. However zone->flags could be split into 2 bitfields to hold enum zone_flags and enum zone_type. 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. -Vineet -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>