On Monday 21 January 2013, Greg KH wrote: > > > > I don't know a lot about USB, but I always assumed that this was not > > a normal condition and that there are only a couple of URBs per endpoint > > used at a time. Maybe Greg or someone else with a USB background can > > shed some light on this. > > There's no restriction on how many URBs a driver can have outstanding at > once, and if you have a system with a lot of USB devices running at the > same time, there could be lots of URBs in flight depending on the number > of host controllers and devices and drivers being used.
Ok, thanks for clarifying that. I read some more of the em28xx driver, and while it does have a bunch of URBs in flight, there are only five audio and five video URBs that I see simultaneously being submitted, and then resubmitted from their completion handlers. I think this means that there should be 10 URBs active at any given time in this driver, which does not explain why we get 256 allocations. I also noticed that the initial submissions are all atomic but don't need to, so it may be worth trying the patch below, which should also help in low-memory situations. We could also try moving the resubmission into a workqueue in order to let those be GFP_KERNEL, but I don't think that will help. Arnd diff --git a/drivers/media/usb/em28xx/em28xx-audio.c b/drivers/media/usb/em28xx/em28xx-audio.c index 2fdb66e..8b789f4 100644 --- a/drivers/media/usb/em28xx/em28xx-audio.c +++ b/drivers/media/usb/em28xx/em28xx-audio.c @@ -177,12 +177,12 @@ static int em28xx_init_audio_isoc(struct em28xx *dev) struct urb *urb; int j, k; - dev->adev.transfer_buffer[i] = kmalloc(sb_size, GFP_ATOMIC); + dev->adev.transfer_buffer[i] = kmalloc(sb_size, GFP_KERNEL); if (!dev->adev.transfer_buffer[i]) return -ENOMEM; memset(dev->adev.transfer_buffer[i], 0x80, sb_size); - urb = usb_alloc_urb(EM28XX_NUM_AUDIO_PACKETS, GFP_ATOMIC); + urb = usb_alloc_urb(EM28XX_NUM_AUDIO_PACKETS, GFP_KERNEL); if (!urb) { em28xx_errdev("usb_alloc_urb failed!\n"); for (j = 0; j < i; j++) { @@ -212,7 +212,7 @@ static int em28xx_init_audio_isoc(struct em28xx *dev) } for (i = 0; i < EM28XX_AUDIO_BUFS; i++) { - errCode = usb_submit_urb(dev->adev.urb[i], GFP_ATOMIC); + errCode = usb_submit_urb(dev->adev.urb[i], GFP_KERNEL); if (errCode) { em28xx_errdev("submit of audio urb failed\n"); em28xx_deinit_isoc_audio(dev); diff --git a/drivers/media/usb/em28xx/em28xx-core.c b/drivers/media/usb/em28xx/em28xx-core.c index bed07a6..c5a2c4b 100644 --- a/drivers/media/usb/em28xx/em28xx-core.c +++ b/drivers/media/usb/em28xx/em28xx-core.c @@ -1166,7 +1166,7 @@ int em28xx_init_isoc(struct em28xx *dev, enum em28xx_mode mode, /* submit urbs and enables IRQ */ for (i = 0; i < isoc_bufs->num_bufs; i++) { - rc = usb_submit_urb(isoc_bufs->urb[i], GFP_ATOMIC); + rc = usb_submit_urb(isoc_bufs->urb[i], GFP_KERNEL); if (rc) { em28xx_err("submit of urb %i failed (error=%i)\n", i, rc); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/