On Fri, Dec 30 2016, Michal Hocko wrote:
> On Fri 30-12-16 16:24:46, Jaewon Kim wrote:
> [...]
>> >From 7577cc94da3af27907aa6eec590d2ef51e4b9d80 Mon Sep 17 00:00:00 2001
>> From: Jaewon Kim <jaewon31.kim@xxxxxxxxxxx>
>> Date: Thu, 29 Dec 2016 11:00:16 +0900
>> Subject: [PATCH] mm: cma: print allocation failure reason and bitmap status
>>
>> There are many reasons of CMA allocation failure such as EBUSY, ENOMEM, EINTR.
>> But we did not know error reason so far. This patch prints the error value.
>>
>> Additionally if CONFIG_CMA_DEBUG is enabled, this patch shows bitmap status to
>> know available pages. Actually CMA internally try all available regions because
>> some regions can be failed because of EBUSY. Bitmap status is useful to know in
>> detail on both ENONEM and EBUSY;
>> ENOMEM: not tried at all because of no available region
>> it could be too small total region or could be fragmentation issue
>> EBUSY: tried some region but all failed
>>
>> This is an ENOMEM example with this patch.
>> [ 13.250961] [1: Binder:715_1: 846] cma: cma_alloc: alloc failed, req-size: 256 pages, ret: -12
>> Avabile pages also will be shown if CONFIG_CMA_DEBUG is enabled
>> [ 13.251052] [1: Binder:715_1: 846] cma: number of available pages: 4@572+7@585+7@601+8@632+38@730+166@1114+127@1921=>357 pages, total: 2048 pages
>
> please mention how to interpret this information.
>
> some more style suggestions below
>>
>> Signed-off-by: Jaewon Kim <jaewon31.kim@xxxxxxxxxxx>
Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx>
>> ---
>> mm/cma.c | 29 ++++++++++++++++++++++++++++-
>> 1 file changed, 28 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/cma.c b/mm/cma.c
>> index c960459..1bcd9db 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);
This line should be moved after the ‘if (ret != 0)’ block, i.e. just
before return.
>> +
>> + if (ret != 0)
>
> you can simply do
> if (!ret) {
>
> pr_info("%s: alloc failed, req-size: %zu pages, ret: %d\n",
> __func__, count, ret);
> debug_show_cma_areas();
> }
>
> return page;
>
> static void debug_show_cma_areas(void)
> {
> #ifdef CONFIG_CMA_DEBUG
> unsigned int nr, nr_total = 0;
> unsigned long next_set_bit;
>
> mutex_lock(&cma->lock);
> pr_info("number of available pages: ");
> start = 0;
> for (;;) {
> bitmap_no = find_next_zero_bit(cma->bitmap, cma->count, start);
> if (bitmap_no >= cma->count)
> break;
> next_set_bit = find_next_bit(cma->bitmap, cma->count, bitmap_no);
> nr = next_set_bit - bitmap_no;
> pr_cont("%s%u@%lu", nr_total ? "+" : "", nr, bitmap_no);
> nr_total += nr;
> start = bitmap_no + nr;
> }
> pr_cont("=>%u pages, total: %lu pages\n", nr_total, cma->count);
Perhaps:
pr_cont("=> %u free of %lu total pages\n", nr_total, cma->count);
or shorter (but more cryptic):
pr_cont("=> %u/%lu pages\n", nr_total, cma->count);
> mutex_unlock(&cma->lock);
> #endif
> }
Actually, Linux style is more like:
#ifdef CONFIG_CMA_DEBUG
static void cma_debug_show_areas()
{
…
}
#else
static inline void cma_debug_show_areas() { }
#endif
>
> --
> 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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