Messages in this thread | | | Date | Wed, 1 Mar 2006 16:57:40 +0100 | From | Jens Axboe <> | Subject | Re: adding swap workarounds oom - was: Re: Out of Memory: Killed process 16498 (java). |
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On Wed, Mar 01 2006, Andy Chittenden wrote: > > On Wed, Mar 01 2006, Andi Kleen wrote: > > > On Wednesday 01 March 2006 15:34, Jens Axboe wrote: > > > > > > > > > > > It shouldn't end up with more, only with less. > > > > > > > > Sure yes, but if that 'less' is still more than what the > > driver can > > > > handle, then there's a problem. > > > > > > The driver needs to handle the full list it passed in. It's quite > > > possible that the iommu layer is unable to merge anything. > > > > > > > > > This isn't the block layer based merging where we guarantee > > > to be able to merge in advance - just lazy after the fact merging. > > > > Yes I realize that, I wonder if the bounce patch screwed something up > > that destroys the block layer merging/accounting. We'll know when Andy > > posts results that dump the request as well. > > And here's the dmesg o/p (I had to gather it from /var/log/kern.log as > there was so much output):
Thanks!
> hda: DMA table too small > ide dma table, 256 entries, bounce pfn 1310720 > sg0: dma=830e800, len=4096/0, pfn=1202633 > sg1: dma=830f800, len=4096/0, pfn=1202590 > sg2: dma=8310800, len=4096/0, pfn=1202548 > sg3: dma=8311800, len=4096/0, pfn=1202506
Alright Andi, take a look at this then. We have the same thing again, mid page start of the sg entries. The block layer has done no merging, it's 256 separate segments. The pci_map_sg() output is the same, except that the IDE driver now needs to split the entries. The corresponding rq entries for the first four above are:
> request: phys seg 256, hw seg 256, nr_sectors 2048 > bio0: bytes=4096, phys seg 1, hw seg 1 > bvec0: addr=ffff8101259c9000, size=4096, off=0 > bio1: bytes=4096, phys seg 1, hw seg 1 > bvec0: addr=ffff81012599e000, size=4096, off=0 > bio2: bytes=4096, phys seg 1, hw seg 1 > bvec0: addr=ffff810125974000, size=4096, off=0 > bio3: bytes=4096, phys seg 1, hw seg 1 > bvec0: addr=ffff81012594a000, size=4096, off=0
these here. Totally plain 4kb bios strung to the request, no funky offsets or anything. 256 hardware and physical segments, for a total of a 1MB request.
So what is going wrong? Why does the pci mapping output looks so "strange"?
-- Jens Axboe
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