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SubjectRe: [PATCH 2/3] mm: cma: introduce /proc/cmainfo
On Fri, Dec 26, 2014 at 05:39:03PM +0300, Stefan I. Strogin wrote:
> /proc/cmainfo contains a list of currently allocated CMA buffers for every
> CMA area when CONFIG_CMA_DEBUG is enabled.

Hello,

I think that providing these information looks useful, but, we need better
implementation. As Laura said, it is better to use debugfs. And,
instead of re-implementing the wheel, how about using tracepoint
to print these information? See below comments.

>
> 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
> @@ -34,6 +34,10 @@
> #include <linux/cma.h>
> #include <linux/highmem.h>
> #include <linux/io.h>
> +#include <linux/list.h>
> +#include <linux/proc_fs.h>
> +#include <linux/uaccess.h>
> +#include <linux/time.h>
>
> struct cma {
> unsigned long base_pfn;
> @@ -41,8 +45,25 @@ struct cma {
> unsigned long *bitmap;
> unsigned int order_per_bit; /* Order of pages represented by one bit */
> struct mutex lock;
> +#ifdef CONFIG_CMA_DEBUG
> + struct list_head buffers_list;
> + struct mutex list_lock;
> +#endif
> };
>
> +#ifdef CONFIG_CMA_DEBUG
> +struct cma_buffer {
> + unsigned long pfn;
> + unsigned long count;
> + pid_t pid;
> + char comm[TASK_COMM_LEN];
> + unsigned int latency;
> + unsigned long trace_entries[16];
> + unsigned int nr_entries;
> + struct list_head list;
> +};
> +#endif
> +
> static struct cma cma_areas[MAX_CMA_AREAS];
> static unsigned cma_area_count;
> static DEFINE_MUTEX(cma_mutex);
> @@ -132,6 +153,10 @@ static int __init cma_activate_area(struct cma *cma)
> } while (--i);
>
> mutex_init(&cma->lock);
> +#ifdef CONFIG_CMA_DEBUG
> + INIT_LIST_HEAD(&cma->buffers_list);
> + mutex_init(&cma->list_lock);
> +#endif
> return 0;
>
> err:
> @@ -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);
> + 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;
> +}
> +
> +/**
> + * cma_buffer_list_del() - delete an entry from a list of allocated buffers
> + * @cma: Contiguous memory region for which the allocation was performed.
> + * @pfn: Base PFN of the released buffer.
> + *
> + * This function deletes a list entry added by cma_buffer_list_add().
> + */
> +static void cma_buffer_list_del(struct cma *cma, unsigned long pfn)
> +{
> + struct cma_buffer *cmabuf;
> +
> + mutex_lock(&cma->list_lock);
> +
> + list_for_each_entry(cmabuf, &cma->buffers_list, list)
> + if (cmabuf->pfn == pfn) {
> + list_del(&cmabuf->list);
> + kfree(cmabuf);
> + goto out;
> + }
> +

Is there more elegant way to find buffer? This linear search overhead
would change system behaviour if there are lots of buffers.

> + pr_err("%s(pfn %lu): couldn't find buffers list entry\n",
> + __func__, pfn);
> +
> +out:
> + mutex_unlock(&cma->list_lock);
> +}
> +#else
> +static int cma_buffer_list_add(struct cma *cma, unsigned long pfn,
> + int count, s64 latency)
> +{
> + return 0;
> +}
> +
> +static void cma_buffer_list_del(struct cma *cma, unsigned long pfn)
> +{
> +}
> +#endif /* CONFIG_CMA_DEBUG */
> +
> /**
> * cma_alloc() - allocate pages from contiguous area
> * @cma: Contiguous memory region for which the allocation is performed.
> @@ -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);
> +
> pr_debug("%s(cma %p, count %d, align %d)\n", __func__, (void *)cma,
> count, align);
>
> @@ -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) {
> + ret = cma_buffer_list_add(cma, pfn, count, latency);
> + if (ret) {
> + pr_warn("%s(): cma_buffer_list_add() returned %d\n",
> + __func__, ret);
> + cma_release(cma, page, count);
> + page = NULL;
> + }

So, we would fail to allocate CMA memory if we can't allocate buffer
for debugging. I don't think it makes sense. With tracepoint,
we don't need to allocate buffer in runtime.

Thanks.



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