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

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Message-ID: <8d7ae527-e0ff-6fa9-7ba3-899a75abc3fa@gmail.com>
Date:   Fri, 19 Mar 2021 16:45:57 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
        joaodias@...gle.com, willy@...radead.org, david@...hat.com,
        surenb@...gle.com, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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 16:39, Dmitry Osipenko пишет:
> 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?
> 
> ...
>>> +void cma_sysfs_alloc_pages_count(struct cma *cma, size_t count)
>>> +{
>>> +	spin_lock(&cma->stat->lock);
>>> +	cma->stat->nr_pages_succeeded += count;
>>> +	spin_unlock(&cma->stat->lock);
>>> +}
>>> +
>>> +void cma_sysfs_fail_pages_count(struct cma *cma, size_t count)
>>> +{
>>> +	spin_lock(&cma->stat->lock);
>>> +	cma->stat->nr_pages_failed += count;
>>> +	spin_unlock(&cma->stat->lock);
>>> +}
> 
> You could use atomic increment and then locking isn't needed.
> 

Actually, the counter should be u64 in order not to worry about overflow.