On Thu, Dec 29 2016, Michal Hocko wrote:
> On Thu 29-12-16 11:28:02, Jaewon Kim wrote:
>> There are many reasons of CMA allocation failure such as EBUSY, ENOMEM, EINTR.
>> This patch prints the error value and bitmap status to know available pages
>> regarding fragmentation.
>>
>> This is an ENOMEM example with this patch.
>> [ 11.616321] [2: Binder:711_1: 740] cma: cma_alloc: alloc failed, req-size: 256 pages, ret: -12
>
>> [ 11.616365] [2: Binder:711_1: 740] number of available pages: 4+7+7+8+38+166+127=>357 pages, total: 2048 pages
>
> Could you be more specific why this part is useful?
>
>> Signed-off-by: Jaewon Kim <jaewon31.kim@xxxxxxxxxxx>
>> ---
>> mm/cma.c | 29 ++++++++++++++++++++++++++++-
>> 1 file changed, 28 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/cma.c b/mm/cma.c
>> index c960459..535aa39 100644
>> --- a/mm/cma.c
>> +++ b/mm/cma.c
>> @@ -369,7 +369,7 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align)
>> unsigned long start = 0;
>> unsigned long bitmap_maxno, bitmap_no, bitmap_count;
>> struct page *page = NULL;
>> - int ret;
>> + int ret = -ENOMEM;
>>
>> if (!cma || !cma->count)
>> return NULL;
>> @@ -427,6 +427,33 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align)
>> trace_cma_alloc(pfn, page, count, align);
>>
>> pr_debug("%s(): returned %p\n", __func__, page);
>> +
>> + if (ret != 0) {
>> + unsigned int nr, nr_total = 0;
>> + unsigned long next_set_bit;
>> +
>> + pr_info("%s: alloc failed, req-size: %zu pages, ret: %d\n",
>> + __func__, count, ret);
>> + mutex_lock(&cma->lock);
>> + printk("number of available pages: ");
>> + start = 0;
>> + for (;;) {
>> + bitmap_no = find_next_zero_bit(cma->bitmap, cma->count, start);
>> + next_set_bit = find_next_bit(cma->bitmap, cma->count, bitmap_no);
>> + nr = next_set_bit - bitmap_no;
>> + if (bitmap_no >= cma->count)
>> + break;
Put this just next to ‘bitmap_no = …’ line. No need to call
find_next_bit if we’re gonna break anyway.
>> + if (nr_total == 0)
>> + printk("%u", nr);
>> + else
>> + printk("+%u", nr);
Perhaps also include location of the hole? Something like:
pr_cont("%s%u@%u", nr_total ? "+" : "", nr, bitmap_no);
>> + nr_total += nr;
>> + start = bitmap_no + nr;
>> + }
>> + printk("=>%u pages, total: %lu pages\n", nr_total, cma->count);
>> + mutex_unlock(&cma->lock);
>> + }
>> +
I wonder if this should be wrapped in
#ifdef CMA_DEBUG
…
#endif
On one hand it’s relatively expensive (even involving mutex locking) on
the other it’s in allocation failure path.
>> return page;
>> }
>>
>> --
>> 1.9.1
>>
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>
> --
> Michal Hocko
> SUSE Labs
--
Best regards
ミハウ “𝓶𝓲𝓷𝓪86” ナザレヴイツ
«If at first you don’t succeed, give up skydiving»
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