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Message-ID: <5dba07eb-88f0-bf84-494e-b979f32ad44d@gmail.com>
Date:   Sun, 8 Oct 2023 19:10:01 +0800
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Subject: Re: [PATCH 2/3] delayacct: convert task->delays to a object
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     bsingharora@gmail.com, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, linux-kernel@vger.kernel.org
References: <cover.1696761522.git.chunguang.xu@shopee.com>
 <531ddc82793a39f4c09316d701a4b1170bcad4ab.1696761522.git.chunguang.xu@shopee.com>
 <20231008105801.GC6320@noisy.programming.kicks-ass.net>
From:   brookxu <brookxu.cn@gmail.com>
In-Reply-To: <20231008105801.GC6320@noisy.programming.kicks-ass.net>
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在 2023/10/8 18:58, Peter Zijlstra 写道:
> On Sun, Oct 08, 2023 at 06:49:37PM +0800, brookxu.cn wrote:
>> From: Chunguang Xu <chunguang.xu@shopee.com>
>>
>> Since in some scenarios we still want to get the task delayacct
>> through taskstats, so commit <0cd7c741f01de> introduces a sysctl to
> This is not the canonical way to reference a commit.
>
>> enable it dynamically. However, since task->delays is allocated
>> during fork(), task->delays will not be reallocated when delayacct
>> is enabled later. This will make we cannot get the delayacct of old
>> tasks, but the new tasks cans. This can easily lead to confusion.
>> Therefore, try to workaround this issue by convert task->delays to
>> an object.
> And grow task_struct for no reason? I think not.
>
>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> index 77f01ac385f7..5cc78184a31f 100644
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -37,6 +37,7 @@
>>   #include <linux/kcsan.h>
>>   #include <linux/rv.h>
>>   #include <linux/livepatch_sched.h>
>> +#include <linux/delayacct.h>
>>   #include <asm/kmap_size.h>
>>   
>>   /* task_struct member predeclarations (sorted alphabetically): */
>> @@ -1331,7 +1332,7 @@ struct task_struct {
>>   	struct page_frag		task_frag;
>>   
>>   #ifdef CONFIG_TASK_DELAY_ACCT
>> -	struct task_delay_info		*delays;
>> +	struct task_delay_info		delays;
>>   #endif
> Yeah, no.
Yes, this way will increase about 80 bytes for task_struct, about 0.85% 
of size of task_struct, I think this just like sched_statistics, so that 
can better support dynamically enable through sysctl.