linux-kernel - Re: [PATCH] mm: cma: print allocation failure reason and bitmap status

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Message-ID: <xa1tmvfahscn.fsf@mina86.com>
Date:   Mon, 02 Jan 2017 07:46:16 +0100
From:   Michal Nazarewicz <mina86@...a86.com>
To:     Jaewon Kim <jaewon31.kim@...sung.com>,
        Michal Hocko <mhocko@...nel.org>
Cc:     gregkh@...uxfoundation.org, akpm@...ux-foundation.org,
        labbott@...hat.com, m.szyprowski@...sung.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, jaewon31.kim@...il.com
Subject: Re: [PATCH] mm: cma: print allocation failure reason and bitmap status

On Mon, Jan 02 2017, Jaewon Kim wrote:
> 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 tries on 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.
> [   12.415458]  [2:   Binder:714_1:  744] cma: cma_alloc: alloc failed, req-size: 256 pages, ret: -12
> If CONFIG_CMA_DEBUG is enabled, avabile pages also will be shown as concatenated
> size@...ition format. So 4@572 means that there are 4 available pages at 572
> position starting from 0 position.
> [   12.415503]  [2:   Binder:714_1:  744] cma: number of available pages: 4@...+7@...+7@...+8@...+38@...+166@...4+127@...1=> 357 free of 2048 total pages
>
> Signed-off-by: Jaewon Kim <jaewon31.kim@...sung.com>
> Acked-by: Michal Nazarewicz <mina86@...a86.com>
> ---
>  mm/cma.c | 34 +++++++++++++++++++++++++++++++++-
>  1 file changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/mm/cma.c b/mm/cma.c
> index c960459..9e037541 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -353,6 +353,32 @@ int __init cma_declare_contiguous(phys_addr_t base,
>      return ret;
>  }
>  
> +#ifdef CONFIG_CMA_DEBUG
> +static void debug_show_cma_areas(struct cma *cma)

Make it ‘cma_debug_show_areas’.  All other functions have ‘cma’ as
prefix so that’s more consistent.

> +{
> +    unsigned long next_zero_bit, next_set_bit;
> +    unsigned long start = 0;
> +    unsigned int nr_zero, nr_total = 0;
> +
> +    mutex_lock(&cma->lock);
> +    pr_info("number of available pages: ");
> +    for (;;) {
> +        next_zero_bit = find_next_zero_bit(cma->bitmap, cma->count, start);
> +        if (next_zero_bit >= cma->count)
> +            break;
> +        next_set_bit = find_next_bit(cma->bitmap, cma->count, next_zero_bit);
> +        nr_zero = next_set_bit - next_zero_bit;
> +        pr_cont("%s%u@%lu", nr_total ? "+" : "", nr_zero, next_zero_bit);
> +        nr_total += nr_zero;
> +        start = next_zero_bit + nr_zero;
> +    }
> +    pr_cont("=> %u free of %lu total pages\n", nr_total, cma->count);
> +    mutex_unlock(&cma->lock);
> +}
> +#else
> +static inline void debug_show_cma_areas(struct cma *cma) { }
> +#endif
> +
>  /**
>   * cma_alloc() - allocate pages from contiguous area
>   * @cma:   Contiguous memory region for which the allocation is performed.
> @@ -369,7 +395,7 @@ 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;
> @@ -426,6 +452,12 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align)
>  
>      trace_cma_alloc(pfn, page, count, align);
>  
> +    if (ret) {
> +        pr_info("%s: alloc failed, req-size: %zu pages, ret: %d\n",
> +            __func__, count, ret);
> +        debug_show_cma_areas(cma);
> +    }
> +
>      pr_debug("%s(): returned %p\n", __func__, page);
>      return page;
>  }
> -- 
>

-- 
Best regards
ミハウ “𝓶𝓲𝓷𝓪86” ナザレヴイツ
«If at first you don’t succeed, give up skydiving»