[Crash-utility] Re: [External Mail]Re: [BUG FIXED]fix bug of CACHED in kmem -i show memory

[薛国伦 <xueguolun@xxxxxxxxxx>]

Hi kazu:

I found that vmlinux of GKI kernel-6.1 which is newest version in links below, it can make sure that nr_swapper_spaces not found.

https://ci.android.com/builds/submitted/11087000/kernel_aarch64/latest?hl=zh-cn

Download vmlinux in links and run: readelf -a vmlinux | grep nr_swapper_spaces

can not find this symbol.

Thanks！

Best Regards

---

From: 薛国伦
Sent: Friday, December 1, 2023 4:07:08 PM
To: HAGIO KAZUHITO(?尾　一仁); devel@xxxxxxxxxxxxxxxxxxxxxxxxxxx
Cc: Lianbo Jiang
Subject: Re: [External Mail]Re: [BUG FIXED]fix bug of CACHED in kmem -i show memory

 

Hi kazu:

1. I know that kernel have nr_swapper_spaces since kernel 4.11 which brought into kernel with struct address_space *swapper_spaces[]

my team think GKI vmlinux did not have nr_swapper_spaces this symbol, may due to compile rule changed in AOSP code.

we will try to find the root cause of vmlinux without symbol name nr_swappera_space.

     >> RELEASE: 6.1.25-android14-11-maybe-dirty-qki-consolidate

     >> crash> nr_swapper_spaces

     >> crash: command not found: nr_swapper_spaces

2. I printf log of crash when execute kmem -i, it run into branch of "symbol_exists("swapper_spaces")", also can not find nr_swapper_spaces

if (symbol_exists("nr_swapper_spaces") {

    ......

} else if (symbol_exists("swapper_spaces") {

    ......

} else if (symbol_exists("swapper_space") {

    ......

}

3. using my patch, it can fix output log of kmem -i which CACHED show not right.

Fix before:

crash> kmem -i

                 PAGES        TOTAL      PERCENTAGE

    TOTAL MEM  2854115      10.9 GB         ----

         FREE   169699     662.9 MB    5% of TOTAL MEM

         USED  2684416      10.2 GB   94% of TOTAL MEM

       SHARED   891094       3.4 GB   31% of TOTAL MEM

      BUFFERS      329       1.3 MB    0% of TOTAL MEM

       CACHED  873327085626  3331478.4 GB  30598875% of TOTAL MEM

         SLAB   230128     898.9 MB    8% of TOTAL MEM

Fix after:

crash> kmem -i

                 PAGES        TOTAL      PERCENTAGE

    TOTAL MEM  2854115      10.9 GB         ----

         FREE   169699     662.9 MB    5% of TOTAL MEM

         USED  2684416      10.2 GB   94% of TOTAL MEM

       SHARED   891094       3.4 GB   31% of TOTAL MEM

      BUFFERS      329       1.3 MB    0% of TOTAL MEM

       CACHED  1729018       6.6 GB   60% of TOTAL MEM

         SLAB   230128     898.9 MB    8% of TOTAL MEM

I think crash tools without my patch, maybe miss some situation like this which symbol miss in kenrel vmlinux.

I think that using both branch of symbol_exist("nr_swapper_spaces") and symbol_exists("swapper_spaces") means to double check

the situation of all kinds of kernel and vmlinux. 

It seen that bring my patch can deal with more unusual situation and make crash tool more compatible.

Thanks！

Best Regards

---

From: HAGIO KAZUHITO(?尾　一仁) <k-hagio-ab@xxxxxxx>
Sent: Friday, December 1, 2023 3:08:03 PM
To: 薛国伦; devel@xxxxxxxxxxxxxxxxxxxxxxxxxxx
Cc: Lianbo Jiang
Subject: Re: [External Mail]Re: [BUG FIXED]fix bug of CACHED in kmem -i show memory

 

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On 2023/11/30 22:05, 薛国伦 wrote:
> Hi kazu:
>
>
> 1. I found that vmlinux of kernel-6.1 did not have symbol nr_swapper_spaces but only have swapper_spaces
>
> Also check in GKI vmlinux, can not find nr_swapper_spaces

Hmm, upstream kernel 6.1 has it.

$ git show v6.1:mm/swap_state.c

struct address_space *swapper_spaces[MAX_SWAPFILES] __read_mostly;
static unsigned int nr_swapper_spaces[MAX_SWAPFILES] __read_mostly;

>
> It may have some problem in symbol of nr_swapper_spaces
>
>
> 2. I think that crash tools will check nr_swapper_spaces first and then check *swapper_spaces, swaper_space[] last.
>
> so first check nr_swapper_spaces not found, crash tool can use *swapper_spaces to enhance compatibility.
>
> The patch i send can resolve this situation which nr_swapper_spaces symbols can not found.

But I cannot determine whether your patch is correct and should be
applied, without kernel patches or the cause of no nr_swapper_spaces.
Could you please find the information (e.g. links) of the related kernel
patches?

Thanks,
Kazu

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