* [PATCH] mm: optimize PageHighMem() check
@ 2015-09-29 7:54 Vineet Gupta
2015-10-01 13:12 ` Michal Hocko
2015-10-01 23:25 ` Andrew Morton
0 siblings, 2 replies; 7+ messages in thread
From: Vineet Gupta @ 2015-09-29 7:54 UTC (permalink / raw)
To: Andrew Morton
Cc: linux-mm, Vineet Gupta, Naoya Horiguchi, Hugh Dickins,
Kirill A. Shutemov, Michal Hocko, Jennifer Herbert,
Konstantin Khlebnikov, linux-kernel
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()
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Jennifer Herbert <jennifer.herbert@citrix.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
---
include/linux/page-flags.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 41c93844fb1d..2953aaa06d67 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -252,7 +252,7 @@ PAGEFLAG(Readahead, reclaim) TESTCLEARFLAG(Readahead, reclaim)
* Must use a macro here due to header dependency issues. page_zone() is not
* available at this point.
*/
-#define PageHighMem(__p) is_highmem(page_zone(__p))
+#define PageHighMem(__p) is_highmem_idx(page_zonenum(__p))
#else
PAGEFLAG_FALSE(HighMem)
#endif
--
1.9.1
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^ permalink raw reply related [flat|nested] 7+ messages in thread* Re: [PATCH] mm: optimize PageHighMem() check
2015-09-29 7:54 [PATCH] mm: optimize PageHighMem() check Vineet Gupta
@ 2015-10-01 13:12 ` Michal Hocko
2015-10-01 23:25 ` Andrew Morton
1 sibling, 0 replies; 7+ messages in thread
From: Michal Hocko @ 2015-10-01 13:12 UTC (permalink / raw)
To: Vineet Gupta
Cc: Andrew Morton, linux-mm, Naoya Horiguchi, Hugh Dickins,
Kirill A. Shutemov, Jennifer Herbert, Konstantin Khlebnikov,
linux-kernel
On Tue 29-09-15 13:24:20, 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 <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()
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> Cc: Michal Hocko <mhocko@suse.cz>
> Cc: Jennifer Herbert <jennifer.herbert@citrix.com>
> Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Looks reasonably to me.
Acked-by: Michal Hocko <mhocko@suse.com>
> ---
> include/linux/page-flags.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 41c93844fb1d..2953aaa06d67 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -252,7 +252,7 @@ PAGEFLAG(Readahead, reclaim) TESTCLEARFLAG(Readahead, reclaim)
> * Must use a macro here due to header dependency issues. page_zone() is not
> * available at this point.
> */
> -#define PageHighMem(__p) is_highmem(page_zone(__p))
> +#define PageHighMem(__p) is_highmem_idx(page_zonenum(__p))
> #else
> PAGEFLAG_FALSE(HighMem)
> #endif
> --
> 1.9.1
--
Michal Hocko
SUSE Labs
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^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] mm: optimize PageHighMem() check
2015-09-29 7:54 [PATCH] mm: optimize PageHighMem() check Vineet Gupta
2015-10-01 13:12 ` Michal Hocko
@ 2015-10-01 23:25 ` Andrew Morton
2015-10-02 7:15 ` Vineet Gupta
1 sibling, 1 reply; 7+ messages in thread
From: Andrew Morton @ 2015-10-01 23:25 UTC (permalink / raw)
To: Vineet Gupta
Cc: linux-mm, Naoya Horiguchi, Hugh Dickins, Kirill A. Shutemov,
Michal Hocko, Jennifer Herbert, Konstantin Khlebnikov,
linux-kernel
On Tue, 29 Sep 2015 13:24:20 +0530 Vineet Gupta <Vineet.Gupta1@synopsys.com> 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?
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^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] mm: optimize PageHighMem() check
2015-10-01 23:25 ` Andrew Morton
@ 2015-10-02 7:15 ` Vineet Gupta
2015-10-02 20:53 ` Andrew Morton
0 siblings, 1 reply; 7+ messages in thread
From: Vineet Gupta @ 2015-10-02 7:15 UTC (permalink / raw)
To: Andrew Morton
Cc: linux-mm, Naoya Horiguchi, Hugh Dickins, Kirill A. Shutemov,
Michal Hocko, Jennifer Herbert, Konstantin Khlebnikov,
linux-kernel
On Friday 02 October 2015 04:55 AM, Andrew Morton wrote:
> On Tue, 29 Sep 2015 13:24:20 +0530 Vineet Gupta <Vineet.Gupta1@synopsys.com> 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
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^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] mm: optimize PageHighMem() check
2015-10-02 7:15 ` Vineet Gupta
@ 2015-10-02 20:53 ` Andrew Morton
2015-10-03 10:19 ` Vineet Gupta
0 siblings, 1 reply; 7+ messages in thread
From: Andrew Morton @ 2015-10-02 20:53 UTC (permalink / raw)
To: Vineet Gupta
Cc: linux-mm, Naoya Horiguchi, Hugh Dickins, Kirill A. Shutemov,
Michal Hocko, Jennifer Herbert, Konstantin Khlebnikov,
linux-kernel
On Fri, 2 Oct 2015 12:45:53 +0530 Vineet Gupta <vgupta@synopsys.com> 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@synopsys.com> 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);
}
> ...
>
> 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.
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^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] mm: optimize PageHighMem() check
2015-10-02 20:53 ` Andrew Morton
@ 2015-10-03 10:19 ` Vineet Gupta
2015-11-06 10:21 ` Vineet Gupta
0 siblings, 1 reply; 7+ messages in thread
From: Vineet Gupta @ 2015-10-03 10:19 UTC (permalink / raw)
To: Andrew Morton
Cc: linux-mm@kvack.org, Naoya Horiguchi, Hugh Dickins,
Kirill A. Shutemov, Michal Hocko, Jennifer Herbert,
Konstantin Khlebnikov, linux-kernel@vger.kernel.org
On Saturday 03 October 2015 02:23 AM, Andrew Morton wrote:
> On Fri, 2 Oct 2015 12:45:53 +0530 Vineet Gupta <vgupta@synopsys.com> 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@synopsys.com> 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
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^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] mm: optimize PageHighMem() check
2015-10-03 10:19 ` Vineet Gupta
@ 2015-11-06 10:21 ` Vineet Gupta
0 siblings, 0 replies; 7+ messages in thread
From: Vineet Gupta @ 2015-11-06 10:21 UTC (permalink / raw)
To: Andrew Morton
Cc: linux-mm@kvack.org, Naoya Horiguchi, Hugh Dickins,
Kirill A. Shutemov, Michal Hocko, Jennifer Herbert,
Konstantin Khlebnikov, linux-kernel@vger.kernel.org, arcml
On Saturday 03 October 2015 03:49 PM, Vineet Gupta wrote:
> On Saturday 03 October 2015 02:23 AM, Andrew Morton wrote:
>> > On Fri, 2 Oct 2015 12:45:53 +0530 Vineet Gupta <vgupta@synopsys.com> 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@synopsys.com> 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
Andrew, what do u think. Do we need to shoehorn type (idx) and flags into same
placeholder or simply add a new zone_idx field.
There will be slight complications with former to avoid any possible collisions
when someone calls set_bit() for flags holder bitfield.
IMHO zone struct is already so bloated, adding another word would be OK specially
when number of zone structures is not too many !
-Vineet
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Thread overview: 7+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2015-09-29 7:54 [PATCH] mm: optimize PageHighMem() check Vineet Gupta
2015-10-01 13:12 ` Michal Hocko
2015-10-01 23:25 ` Andrew Morton
2015-10-02 7:15 ` Vineet Gupta
2015-10-02 20:53 ` Andrew Morton
2015-10-03 10:19 ` Vineet Gupta
2015-11-06 10:21 ` Vineet Gupta
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