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? -- 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>