problem with bus_dmamap_load_uio

[Patrick Lamaizière]

Hello,

(8-Current/i386)

I've got a problem with bus_dmamap_load_uio(9). I want to use it to
map an uio for DMA with the Geode security block (glxsb(4)).

It works, i can make milions of crypto operations with cryptotest.

But when (i guess, i'm not sure) the free memory becomes low,
bus_dmamap_load_uio() fails with errno == EFBIG.

I can reproduce the problem by running "periodic daily", "dd
if=/dev/zero of=foo", ...

By sample i run into problems with Mem: 33M Active, 310M Inact, 82M
Wired, 60M Buf, 69M Free.

When it fails the uio is :
uio_segflg = UIO_SYSSPACE
uio_iovcnt = 1, 
totlen = 16384 (the total length for iov)
uio_resid = 16384

(i've got some failure with size between 4000 and 16384)

I don't understand why bus_dmamap_load_uio() cannot load the uio. Also
when it fails, i copy the uio into a buffer and then a
bus_dmamap_load() of the buffer always works.

The dma tag is allocated with:

bus_dma_tag_create(bus_get_dma_tag(sc->sc_dev),/* parent */
 16, 0,                   /* alignments, bounds */
 BUS_SPACE_MAXADDR_32BIT, /* lowaddr */
 BUS_SPACE_MAXADDR,       /* highaddr */
 NULL, NULL,              /* filter, filterarg */
 16384,                   /* maxsize */
 1,                       /* nsegments */
 16384,                   /* maxsegsize */
 BUS_DMA_ALLOCNOW,        /* flags */
 NULL, NULL,              /* lockfunc, lockarg */
 &sc->sc_dmat);

The dma map is created just before the bus_dmamap_load_uio() and
destroyed later.

(source : http://user.lamaiziere.net/patrick/glxsb.c , see
glxsb_crypto_encdec() ).

I'm trying to understand and fix this problem for several days, so any
idea will be very cool...

thanks, regards.