From owner-freebsd-hackers  Wed Mar 13 12:20:51 2002
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Date: Wed, 13 Mar 2002 14:19:47 -0600 (CST)
From: mark tinguely <tinguely@web.cs.ndsu.nodak.edu>
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To: freebsd-hackers@FreeBSD.ORG, gjohnson@research.canon.com.au
Subject: Re: DMA memory allocation/deallocation
In-Reply-To: <20020313000243.0B01F540D0@brixi.research.canon.com.au>
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>  I am having some memory allocation woes in my FreeBSD kernel
>  device driver. I allocate DMAable memory with something like:
>
>      retval = bus_dma_tag_create
...
>          (1 << 20),
>          1,
>          (1 << 20),
...

>  which seems to succeed/work. But when I attempt to release the
>  allocated memory like this:
>
>      bus_dmamap_unload(memtag, memmap);
>
>      bus_dmamem_free(memtag, (void *) vaddr, memmap);
>
>      bus_dmamap_destroy(memtag, memmap);
>
>      bus_dma_tag_destroy(memtag);

there was a contig_free bug that was squashed between 4.4 and 4.5,
by Matt Dillon. If I remember correctly there is a slight leak if
the contig_malloc failed, but that would not be your problem.

it is possible that something else on the system is allocating at least
single block in that now freed, but perfect sized chunk. as a result,
the new allocation can no longer use that memory and has to search higher
in RAM.

try a few back to back bus_dmamem_alloc() and bus_dmamem_free() without
any other operations and if that is sliding up in RAM there is a(nother)
problem in the contiguous free...my guess it will operate normally and
the problem is related to someone allocating a block and breaking up
that nice contiguous chunk.

--mark tinguely.

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