From: "孙世龙 sunshilong" <sunshilong369@gmail.com>
To: "Valdis Klētnieks" <valdis.kletnieks@vt.edu>
Cc: Kernelnewbies@kernelnewbies.org
Subject: Re: Why does “page allocation failure” occur whereas there are still “58*4096kB (C)” could be used?
Date: Fri, 19 Jun 2020 14:56:20 +0800 [thread overview]
Message-ID: <CAAvDm6aiqYuRL3=pVq=_j18=o+6z+wb-zdrLnkKRqWnuG_bTrA@mail.gmail.com> (raw)
In-Reply-To: <459330.1592542115@turing-police>
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>> Why does "page allocation failure" occur whereas there are still
"58*4096kB
>> (C)"(*I think it indicates there are 58 order 10 memory could be used*)
>> could be used?
>>
>> Here is the related log:
>>
>> [ 2161.623563] xxxx: page allocation failure: order:10,
>> mode:0x2084020(GFP_ATOMIC|__GFP_COMP)
>
>If you look at the source for alloc_ap_req(), you find it wants
GFP_ATOMIC, not
>CMA. And your box is fresh out of contiguous order-10 spaces that aren't
CMA,
>and you're down to your last 3 order-9 flagged as (UEC).
Thank you for the clarification.
I understand it on a deeper level with your help.
Why doesn't the kernel use two memory blocks whose size is 2048KB(i.e.*oder
9 *)
instead of one block *order 10 *(you see, there are still three free blocks
and
2048KB*2=4096KB equivalent to the memory size of order 10)?
>If you look at the source for alloc_ap_req(), you find it wants
GFP_ATOMIC, not
>CMA.
I followed your advice and read the related source code carefully.
It's corresponding to the log(i.e. mode:0x2084020(GFP_ATOMIC|__GFP_COMP)
).
Thank you for your attention to this matter.
Look forward to hearing from you.
Best regards.
Valdis Klētnieks <valdis.kletnieks@vt.edu> 于2020年6月19日周五 下午12:48写道:
> On Thu, 18 Jun 2020 14:21:05 +0800, sunshiong said:
>
> > Why does "page allocation failure" occur whereas there are still
> "58*4096kB
> > (C)"(*I think it indicates there are 58 order 10 memory could be used*)
> > could be used?
> >
> > Here is the related log:
> >
> > [ 2161.623563] xxxx: page allocation failure: order:10,
> > mode:0x2084020(GFP_ATOMIC|__GFP_COMP)
>
> Most likely, the allocation wanted some other type of allocation.
> The (C) on the order-10 says it's an CMA area.
>
> static const char types[MIGRATE_TYPES] = {
> [MIGRATE_UNMOVABLE] = 'U',
> [MIGRATE_MOVABLE] = 'M',
> [MIGRATE_RECLAIMABLE] = 'E',
> [MIGRATE_HIGHATOMIC] = 'H',
> #ifdef CONFIG_CMA
> [MIGRATE_CMA] = 'C',
> #endif
> #ifdef CONFIG_MEMORY_ISOLATION
> [MIGRATE_ISOLATE] = 'I',
> #endif
>
> If the call was for an unmovable, movable, reclaimable, or highatomic
> allocation, you lose.
>
> If you look at the source for alloc_ap_req(), you find it wants
> GFP_ATOMIC, not
> CMA. And your box is fresh out of contiguous order-10 spaces that aren't
> CMA,
> and you're down to your last 3 order-9 flagged as (UEC).
>
> I admit I find it a tad suspicious that the USB gadget driver asks for a 4M
> chunk of memory. Does USB actually support single transfers that large?
> (I'm
> not a USB expert)
>
>
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next prev parent reply other threads:[~2020-06-19 6:57 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-18 6:21 Why does “page allocation failure” occur whereas there are still “58*4096kB (C)” could be used? 孙世龙
2020-06-19 4:48 ` Valdis Klētnieks
2020-06-19 6:56 ` 孙世龙 sunshilong [this message]
2020-06-19 7:14 ` Valdis Klētnieks
2020-06-20 5:53 ` 孙世龙 sunshilong
2020-06-20 9:51 ` Valdis Klētnieks
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