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

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Date:   Fri, 19 Mar 2021 15:27:52 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Dmitry Osipenko <digetx@...il.com>
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

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?