linux-kernel - Re: [PATCH v4] mm: cma: support sysfs

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Message-ID: <78883205-e6da-5bc4-dcec-b6eb921567b1@gmail.com>
Date:   Fri, 19 Mar 2021 18:38:00 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, joaodias@...gle.com,
        willy@...radead.org, david@...hat.com, surenb@...gle.com,
        John Hubbard <jhubbard@...dia.com>,
        Nicolas Chauvet <kwizart@...il.com>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v4] mm: cma: support sysfs

19.03.2021 17:27, Greg Kroah-Hartman пишет:
> On Fri, Mar 19, 2021 at 05:19:47PM +0300, Dmitry Osipenko wrote:
>> 19.03.2021 16:51, Dmitry Osipenko пишет:
>>> 19.03.2021 16:47, Greg Kroah-Hartman пишет:
>>>> On Fri, Mar 19, 2021 at 04:45:21PM +0300, Dmitry Osipenko wrote:
>>>>> 19.03.2021 16:42, Greg Kroah-Hartman пишет:
>>>>>> On Fri, Mar 19, 2021 at 04:39:41PM +0300, Dmitry Osipenko wrote:
>>>>>>> 19.03.2021 15:44, Dmitry Osipenko пишет:
>>>>>>> ...
>>>>>>>>>  #include <linux/debugfs.h>
>>>>>>>>> +#include <linux/kobject.h>
>>>>>>>>> +
>>>>>>>>> +struct cma_stat {
>>>>>>>>> +	spinlock_t lock;
>>>>>>>>> +	/* the number of CMA page successful allocations */
>>>>>>>>> +	unsigned long nr_pages_succeeded;
>>>>>>>>> +	/* the number of CMA page allocation failures */
>>>>>>>>> +	unsigned long nr_pages_failed;
>>>>>>>>> +	struct kobject kobj;
>>>>>>>>> +};
>>>>>>>>>  
>>>>>>>>>  struct cma {
>>>>>>>>>  	unsigned long   base_pfn;
>>>>>>>>> @@ -16,6 +26,9 @@ struct cma {
>>>>>>>>>  	struct debugfs_u32_array dfs_bitmap;
>>>>>>>>>  #endif
>>>>>>>>>  	char name[CMA_MAX_NAME];
>>>>>>>>> +#ifdef CONFIG_CMA_SYSFS
>>>>>>>>> +	struct cma_stat	*stat;
>>>>>>>>> +#endif
>>>>>>>
>>>>>>> What is the point of allocating stat dynamically?
>>>>>>
>>>>>> Because static kobjects make me cry.
>>>>>>
>>>>>
>>>>> I meant that it's already a part of struct cma, it looks like the stat
>>>>> could be embedded into struct cma and then kobj could be initialized
>>>>> separately.
>>>>
>>>> But that structure is statically allocated, so it can not be.  This has
>>>> been discussed in the past threads for when this was reviewed if you are
>>>> curious :)
>>>
>>> Indeed, I missed that cma_areas[] is static, thank you.
>>>
>>
>> And in this case should be better to make only the kobj allocated
>> dynamically instead of the whole cma_stat.
> 
> Why does it matter?
> 

Then initialization order won't be a problem.