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    SubjectRe: [PATCH 04/10] dmapool: improve accuracy of debug statistics
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    On 2022-05-31 19:17, Tony Battersby wrote:
    > The "total number of blocks in pool" debug statistic currently does not
    > take the boundary value into account, so it diverges from the "total
    > number of blocks in use" statistic when a boundary is in effect. Add a
    > calculation for the number of blocks per allocation that takes the
    > boundary into account, and use it to replace the inaccurate calculation.
    >
    > This depends on the patch "dmapool: fix boundary comparison" for the
    > calculated blks_per_alloc value to be correct.
    >
    > Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
    > ---
    > mm/dmapool.c | 7 +++++--
    > 1 file changed, 5 insertions(+), 2 deletions(-)
    >
    > diff --git a/mm/dmapool.c b/mm/dmapool.c
    > index 782143144a32..9e30f4425dea 100644
    > --- a/mm/dmapool.c
    > +++ b/mm/dmapool.c
    > @@ -47,6 +47,7 @@ struct dma_pool { /* the pool */
    > struct device *dev;
    > unsigned int allocation;
    > unsigned int boundary;
    > + unsigned int blks_per_alloc;
    > char name[32];
    > struct list_head pools;
    > };
    > @@ -92,8 +93,7 @@ static ssize_t pools_show(struct device *dev, struct device_attribute *attr, cha
    > /* per-pool info, no real statistics yet */
    > temp = scnprintf(next, size, "%-16s %4zu %4zu %4u %2u\n",

    Nit: if we're tinkering with this, it's probably worth updating the
    whole function to use sysfs_emit{_at}().

    > pool->name, blocks,
    > - (size_t) pages *
    > - (pool->allocation / pool->size),
    > + (size_t) pages * pool->blks_per_alloc,
    > pool->size, pages);
    > size -= temp;
    > next += temp;
    > @@ -168,6 +168,9 @@ struct dma_pool *dma_pool_create(const char *name, struct device *dev,
    > retval->size = size;
    > retval->boundary = boundary;
    > retval->allocation = allocation;
    > + retval->blks_per_alloc =
    > + (allocation / boundary) * (boundary / size) +
    > + (allocation % boundary) / size;

    Do we really need to store this? Sure, 4 divisions (which could possibly
    be fewer given the constraints on boundary) isn't the absolute cheapest
    calculation, but I still can't imagine anyone would be polling sysfs
    stats hard enough to even notice.

    Thanks,
    Robin.

    >
    > INIT_LIST_HEAD(&retval->pools);
    >

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