On Fri, 2008-04-25 at 12:29 -0500, James Bottomley wrote: > On Thu, 2008-04-24 at 23:33 +0200, Miquel van Smoorenburg wrote: > > > > > memset(msg, 0, sizeof(msg)); > > - buf = kmalloc(80,GFP_KERNEL|ADDR32); > > + buf = pci_alloc_consistent(pHba->pDev, 80, &addr); > > You probably want to use dma_alloc_coherent here ... it's identical to > pci_alloc_consistent in almost every way, except that it allows you to > pass in the GFP_KERNEL flag (pci_alloc_consistent has to assume > GFP_ATOMIC and thus you can get unexpected failures if SLUB is having a > bad day) and you have to call it on &pHba->pDev->dev and use the > corresponding dma_free_coherent(). I actually did that in the next patch, but I have been looking a bit deeper into this and it might not be such a good idea. That, or there is a bug in pci-dma_64.c. In arch/x86/kernel/pci-dma_64.c , dma_alloc_coherent() adds __GFP_NORETRY to the gfp flags before it calls __get_free_pages (through dma_alloc_pages). That means dma_alloc_coherent() -> __get_free_pages() can fail quite easily on x86_64 with GFP_KERNEL. If in __get_free_pages() try_to_free_pages() fails once, and __GFP_NORETRY is set, there is .. well .. no retry :) But why does dma_alloc_coherent() on x86_64 set __GFP_NORETRY ? It says "don't invoke OOM killer" but I think it has more side affects than that: easier failure. Now I think I know why the 3ware management utility tw_cli crashes a lot on my 64-bit boxes with a large diskwrite load ... I've fixed that now by commenting out gfp |= __GFP_NORETRY . Note that pci-dma_32.c in 2.6.25 does not do this, but in 2.6.26-rc3 the two have been merged and __GFP_NORETRY is set for x86_32 as well now. Is that a good idea ? Perhaps a __GFP_NO_OOMKILL ? Mike. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
