Re: [PATCH v7] NVMe: conversion to blk-mq

Matthew Wilcox
2014-06-11T17:09:26Z

On Wed, Jun 11, 2014 at 10:54:52AM -0600, Jens Axboe wrote:
> OK, so essentially any single request must be a virtually contig piece
> of memory. Is there any size limitations to how big this contig segment
> can be?

The maximum size of an I/O is 65536 sectors. So on a 512-byte sector
device, that's 32MB, but on a 4k sector size device, that's 128MB.

> I think this is unique requirement, at least I haven't seen other pieces
> of hardware have it. But it would be pretty trivial to add a setting to
> limit merges based on virtually contig, similarly to what is done for
> number of physical segments.

I think there might be an FCoE device with that requirement too.