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    SubjectRe: [PATCH] mm: cma: print allocation failure reason and bitmap status
    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@samsung.com>
    > 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@samsung.com>
    > ---
    > 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);
    > +
    > + 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);
    mutex_unlock(&cma->lock);
    #endif
    }

    --
    Michal Hocko
    SUSE Labs

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