Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v4] mm: cma: support sysfs
From:   Dmitry Osipenko <digetx@gmail.com>
To:     Minchan Kim <minchan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-mm <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
        joaodias@google.com, willy@infradead.org, david@redhat.com,
        surenb@google.com, Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        John Hubbard <jhubbard@nvidia.com>,
        Nicolas Chauvet <kwizart@gmail.com>,
        "linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>
References: <20210309062333.3216138-1-minchan@kernel.org>
 <fead70a2-4330-79ff-e79a-d8511eab1256@gmail.com>
 <e8ae901d-9521-8de4-ee45-18cb55b8f29c@gmail.com>
Message-ID: <8d7ae527-e0ff-6fa9-7ba3-899a75abc3fa@gmail.com>
Date:   Fri, 19 Mar 2021 16:45:57 +0300
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.8.1
MIME-Version: 1.0
In-Reply-To: <e8ae901d-9521-8de4-ee45-18cb55b8f29c@gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Precedence: bulk

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.