linux-kernel - Re: [PATCH] vmscan: prevent background aging of anon page in no swap system

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Date:	Tue, 31 Aug 2010 10:36:25 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Ying Han <yinghan@...gle.com>, Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Venkatesh Pallipadi <venki@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH] vmscan: prevent background aging of anon page in no swap system

On Tue, Aug 31, 2010 at 10:18 AM, KOSAKI Motohiro
<kosaki.motohiro@...fujitsu.com> wrote:
>> Hi, KOSAKI.
>>
>> On Tue, Aug 31, 2010 at 9:56 AM, KOSAKI Motohiro
>> <kosaki.motohiro@...fujitsu.com> wrote:
>> >> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> >> index 1b145e6..0b8a3ce 100644
>> >> --- a/mm/vmscan.c
>> >> +++ b/mm/vmscan.c
>> >> @@ -1747,7 +1747,7 @@ static void shrink_zone(int priority, struct zone *zone,
>> >>          * Even if we did not try to evict anon pages at all, we want to
>> >>          * rebalance the anon lru active/inactive ratio.
>> >>          */
>> >> -       if (inactive_anon_is_low(zone, sc) && nr_swap_pages > 0)
>> >> +       if (nr_swap_pges > 0 && inactive_anon_is_low(zone, sc))
>> >
>> > Sorry, I don't find any difference. What is your intention?
>> >
>>
>> My intention is that smart gcc can compile out inactive_anon_is_low
>> call in case of non swap configurable system.
>
> Do you really check it on your gcc? nr_swap_pages is not file scope variable, it's
> global variable. afaik, current gcc's link time optimization is not so cool.

#else /* CONFIG_SWAP */

#define nr_swap_pages                           0L
#define total_swap_pages                        0L
#define total_swapcache_pages                   0UL

>
> Do you have a disassemble list?
>

environment for test :
gcc : arm-none-linux-gnueabi-gcc (Sourcery G++ Lite 2009q3-67) 4.4.1
kernel : 2.6.28(for test, I used my working kernel version with my patch)
assembled function is shrink_zone.
(Please understand web gmail's contents mangling. Google guys! Please
repair for like me who can't use SMTP in company. :( )

1. swap configurable version

    1cd0:       e51b303c        ldr     r3, [fp, #-60]  ; 0x3c
    1cd4:       e3530000        cmp     r3, #0
    1cd8:       1affffd1        bne     1c24 <shrink_zone+0x23c>
    1cdc:       e5879004        str     r9, [r7, #4]
    1ce0:       e1a00008        mov     r0, r8
    1ce4:       e1a01007        mov     r1, r7
    1ce8:       e1a04008        mov     r4, r8
    1cec:       ebfff8eb        bl      a0 <inactive_anon_is_low>     <==
    1cf0:       e1a05007        mov     r5, r7
    1cf4:       e3500000        cmp     r0, #0
    1cf8:       0a000006        beq     1d18 <shrink_zone+0x330>
    1cfc:       e1a01008        mov     r1, r8
    1d00:       e1a03006        mov     r3, r6
    1d04:       e3a00020        mov     r0, #32
    1d08:       e1a02007        mov     r2, r7
    1d0c:       e3a0c000        mov     ip, #0
    1d10:       e58dc000        str     ip, [sp]
    1d14:       ebfffa98        bl      77c <shrink_active_list>
    1d18:       e5950008        ldr     r0, [r5, #8]
    1d1c:       ebfffffe        bl      0 <throttle_vm_writeout>
    1d20:       e24bd028        sub     sp, fp, #40     ; 0x28

2. non swap configurable version

    1994:       e3530000        cmp     r3, #0
    1998:       0a000003        beq     19ac <shrink_zone+0x170>
    199c:       e598300c        ldr     r3, [r8, #12]
    19a0:       e593300c        ldr     r3, [r3, #12]
    19a4:       e3130701        tst     r3, #262144     ; 0x40000
    19a8:       0a000008        beq     19d0 <shrink_zone+0x194>
    19ac:       e51b3044        ldr     r3, [fp, #-68]  ; 0x44
    19b0:       e3530000        cmp     r3, #0
    19b4:       1affffd7        bne     1918 <shrink_zone+0xdc>
    19b8:       e51b3038        ldr     r3, [fp, #-56]  ; 0x38
    19bc:       e3530000        cmp     r3, #0
    19c0:       1affffd4        bne     1918 <shrink_zone+0xdc>
    19c4:       e51b303c        ldr     r3, [fp, #-60]  ; 0x3c
    19c8:       e3530000        cmp     r3, #0
    19cc:       1affffd1        bne     1918 <shrink_zone+0xdc>
    19d0:       e586a004        str     sl, [r6, #4]
    19d4:       e1a04006        mov     r4, r6
    19d8:       e5960008        ldr     r0, [r6, #8]
    19dc:       ebfffffe        bl      0 <throttle_vm_writeout>
    19e0:       e24bd028        sub     sp, fp, #40     ; 0x28

-- 
Kind regards,
Minchan Kim
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