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    SubjectRe: adding swap workarounds oom - was: Re: Out of Memory: Killed process 16498 (java).
    Date
    On Wednesday 01 March 2006 15:18, Jens Axboe wrote:
    > On Wed, Mar 01 2006, Andi Kleen wrote:
    > > On Wednesday 01 March 2006 14:41, Jens Axboe wrote:
    > > > On Wed, Mar 01 2006, Andy Chittenden wrote:
    > > > > with revised patch that does:
    > > > >
    > > > > printk("sg%d: dma=%llx, dma_len=%u/%u, pfn=%lu\n", i,
    > > > > (unsigned long long) sg->dma_address, sg->dma_length, sg->offset,
    > > > > page_to_pfn(sg->page));
    > > >
    > > > That is correct, thanks!
    > > >
    > > > > hda: DMA table too small
    > > > > ide dma table, 255 entries, bounce pfn 1310720
    > > > > sg0: dma=81c8800, dma_len=4096/0, pfn=1296369
    > > >
    > > > Still the same badness here, it's 2kb into a page so straddles two pages
    > > > for one entry.
    > >
    > > That's normal if it was in the IOMMU and a merged entry.
    > >
    > > You can try iommu=nomerge.
    > >
    > > Or maybe the higher layers are passing in physically continuous pages
    > > that get merged? Not too unlikely at boot.
    >
    > But that would have to be 1kb or 512b io going in

    Yes. Why not?

    > , I would expect 4kb to
    > be the base entries for any normal type of setup (with a 4kb fs). The
    > 8kb could be one such merged entry, I agree.

    Probably yes.

    > > > Andi, any idea what is going on here? Why is this throwing up all of a
    > > > sudden??
    > >
    > > What is throwing up exactly?
    > >
    > > There was a change recently in the merging algorithm, but it shouldn't
    > > cause any bad side effects for correct users of *_map_sg()
    >
    > That the request we end up passing to blk_rq_map_sg() and then to
    > pci_map_sg() ends up with more entries than the driver advertised. So
    > far I think only Andy reported this, and then only with your
    > blk_queue_bounce_limit() patch applied.

    It shouldn't end up with more, only with less.

    Does iommu=nomerge make a difference?

    -Andi

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