• Jens Axboe's avatar
    nvme-pci: limit max IO size and segments to avoid high order allocations · 943e942e
    Jens Axboe authored
    nvme requires an sg table allocation for each request. If the request
    is large, then the allocation can become quite large. For instance,
    with our default software settings of 1280KB IO size, we'll need
    10248 bytes of sg table. That turns into a 2nd order allocation,
    which we can't always guarantee. If we fail the allocation, blk-mq
    will retry it later. But there's no guarantee that we'll EVER be
    able to allocate that much contigious memory.
    
    Limit the IO size such that we never need more than a single page
    of memory. That's a lot faster and more reliable. Then back that
    allocation with a mempool, so that we know we'll always be able
    to succeed the allocation at some point.
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
    Acked-by: default avatarKeith Busch <keith.busch@intel.com>
    Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
    943e942e
nvme.h 14.2 KB