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SubjectRe: [PATCH 2/3] mm: cma: introduce /proc/cmainfo


2014-12-29 오후 11:09에 Stefan Strogin 이(가) 쓴 글:
> Thanks for review Michał,
>
> On 12/26/2014 07:02 PM, Michal Nazarewicz wrote:
>> On Fri, Dec 26 2014, "Stefan I. Strogin" <s.strogin@partner.samsung.com> wrote:
>>> /proc/cmainfo contains a list of currently allocated CMA buffers for every
>>> CMA area when CONFIG_CMA_DEBUG is enabled.
>>>
>>> Format is:
>>>
>>> <base_phys_addr> - <end_phys_addr> (<size> kB), allocated by <PID>\
>>> (<command name>), latency <allocation latency> us
>>> <stack backtrace when the buffer had been allocated>
>>>
>>> Signed-off-by: Stefan I. Strogin <s.strogin@partner.samsung.com>
>>> ---
>>> mm/cma.c | 202 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>> 1 file changed, 202 insertions(+)
>>>
>>> diff --git a/mm/cma.c b/mm/cma.c
>>> index a85ae28..ffaea26 100644
>>> --- a/mm/cma.c
>>> +++ b/mm/cma.c
>>> @@ -347,6 +372,86 @@ err:
>>> return ret;
>>> }
>>>
>>> +#ifdef CONFIG_CMA_DEBUG
>>> +/**
>>> + * cma_buffer_list_add() - add a new entry to a list of allocated buffers
>>> + * @cma: Contiguous memory region for which the allocation is performed.
>>> + * @pfn: Base PFN of the allocated buffer.
>>> + * @count: Number of allocated pages.
>>> + * @latency: Nanoseconds spent to allocate the buffer.
>>> + *
>>> + * This function adds a new entry to the list of allocated contiguous memory
>>> + * buffers in a CMA area. It uses the CMA area specificated by the device
>>> + * if available or the default global one otherwise.
>>> + */
>>> +static int cma_buffer_list_add(struct cma *cma, unsigned long pfn,
>>> + int count, s64 latency)
>>> +{
>>> + struct cma_buffer *cmabuf;
>>> + struct stack_trace trace;
>>> +
>>> + cmabuf = kmalloc(sizeof(struct cma_buffer), GFP_KERNEL);
>>
>> cmabuf = kmalloc(sizeof *cmabuf, GFP_KERNEL);
>
> cmabuf = kmalloc(sizeof(*cmabuf), GFP_KERNEL);
>
>>
>>> + if (!cmabuf)
>>> + return -ENOMEM;
>>> +
>>> + trace.nr_entries = 0;
>>> + trace.max_entries = ARRAY_SIZE(cmabuf->trace_entries);
>>> + trace.entries = &cmabuf->trace_entries[0];
>>> + trace.skip = 2;
>>> + save_stack_trace(&trace);
>>> +
>>> + cmabuf->pfn = pfn;
>>> + cmabuf->count = count;
>>> + cmabuf->pid = task_pid_nr(current);
>>> + cmabuf->nr_entries = trace.nr_entries;
>>> + get_task_comm(cmabuf->comm, current);
>>> + cmabuf->latency = (unsigned int) div_s64(latency, NSEC_PER_USEC);
>>> +
>>> + mutex_lock(&cma->list_lock);
>>> + list_add_tail(&cmabuf->list, &cma->buffers_list);
>>> + mutex_unlock(&cma->list_lock);
>>> +
>>> + return 0;
>>> +}

Is it ok if the information is too big?
I'm not sure but I remember that seq_printf has 4K limitation.

So I made seq_operations with seq_list_start/next functions.

EX)

static void *debug_seq_start(struct seq_file *s, loff_t *pos)
{
» mutex_lock(&debug_lock);
» return seq_list_start(&debug_list, *pos);
}

static void debug_seq_stop(struct seq_file *s, void *data)
{
» struct debug_header *header = data;

» if (header == NULL || &header->head_list == &debug_list) {
» » seq_printf(s, "end of info");
» }

» mutex_unlock(&debug_lock);
}

static void *debug_seq_next(struct seq_file *s, void *data, loff_t *pos)
{
» return seq_list_next(data, &debug_list, pos);
}

static int debug_seq_show(struct seq_file *sfile, void *data)
{
» struct debug_header *header;
» char *p;

» header= list_entry(data,
» » » struct debug_header,
» » » head_list);

» seq_printf(sfile, "print info");
» return 0;
}
static const struct seq_operations debug_seq_ops = {
» .start = debug_seq_start,
» .next = debug_seq_next,
» .stop = debug_seq_stop,
» .show = debug_seq_show,
};

>> You do not have guarantee that CMA deallocations will match allocations
>> exactly. User may allocate CMA region and then free it chunks. I'm not
>> saying that the debug code must handle than case but at least I would
>> like to see a comment describing this shortcoming.
>
> Thanks, I'll fix it. If a number of released pages is less than there
> were allocated then the list entry shouldn't be deleted, but it's fields
> should be updated.
>
>>
>>> @@ -361,11 +466,15 @@ struct page *cma_alloc(struct cma *cma, int count, unsigned int align)
>>> unsigned long mask, offset, pfn, start = 0;
>>> unsigned long bitmap_maxno, bitmap_no, bitmap_count;
>>> struct page *page = NULL;
>>> + struct timespec ts1, ts2;
>>> + s64 latency;
>>> int ret;
>>>
>>> if (!cma || !cma->count)
>>> return NULL;
>>>
>>> + getnstimeofday(&ts1);
>>> +
>>
>> If CMA_DEBUG is disabled, you waste time on measuring latency. Either
>> use #ifdef or IS_ENABLED, e.g.:
>>
>> if (IS_ENABLED(CMA_DEBUG))
>> getnstimeofday(&ts1);
>
> Obviously! :)
>
>>
>>> @@ -413,6 +522,19 @@ struct page *cma_alloc(struct cma *cma, int count, unsigned int align)
>>> start = bitmap_no + mask + 1;
>>> }
>>>
>>> + getnstimeofday(&ts2);
>>> + latency = timespec_to_ns(&ts2) - timespec_to_ns(&ts1);
>>> +
>>> + if (page) {
>>
>> if (IS_ENABLED(CMA_DEBUG) && page) {
>> getnstimeofday(&ts2);
>> latency = timespec_to_ns(&ts2) - timespec_to_ns(&ts1);
>>
>>> + ret = cma_buffer_list_add(cma, pfn, count, latency);
>>
>> You could also change cma_buffer_list_add to take ts1 as an argument
>> instead of latency and then latency calculating would be hidden inside
>> of that function. Initialising ts1 should still be guarded with
>> IS_ENABLED of course.
>
> if (IS_ENABLED(CMA_DEBUG) && page) {
> getnstimeofday(&ts2);
> latency = timespec_to_ns(&ts2) - timespec_to_ns(&ts1);
>
> It seem to me this variant is better readable, thanks.
>
>>
>>> + if (ret) {
>>> + pr_warn("%s(): cma_buffer_list_add() returned %d\n",
>>> + __func__, ret);
>>> + cma_release(cma, page, count);
>>> + page = NULL;
>>
>> Harsh, but ok, if you want.
>
> Excuse me, maybe you could suggest how to make a nicer fallback?
> Or sure OK?
>
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