On Saturday 03 October 2015 02:23 AM, Andrew Morton wrote:
> On Fri, 2 Oct 2015 12:45:53 +0530 Vineet Gupta <vgupta@xxxxxxxxxxxx> wrote:
>
>> 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.
> Yes it will!
>
> static inline int is_highmem(struct zone *zone)
> {
> return test_bit(ZONE_HIGHMEM, &zone->flags);
> }
Point is do we want to fix this specific case, or do we want to improve zone_idx()
in general.
#define zone_idx(zone) ((zone) - (zone)->zone_pgdat->node_zones
If former, I can split up zone->flags into 31:1 bit-field. Otherwise I will split
it into 24:8 to hold both zone_flags and 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.
> yup.
Do u want me to carry this as part of the the ARC HIGHMEM/PAE40 patchset or would
you rather prefer merging it via mm tree.
Thx,
-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