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SubjectRe: [PATCH 1/2] aio: add vectored I/O support
Joel Becker wrote:

>>I think what happened was that the number of iocbs submitted (64 iocbs
>>of 4K each) did not merge because the device queue depth was very large;
>>no queuing occured because (I imagine) merging happens while a request
>>is waiting for disk readiness.
> Why did you submit 64 iocbs of 4K? Was every page virtually
>discontiguous, or did you arbitrarily decide to create a worst-case?
The application (a userspace filesystem with its own cache) manages
memory in 4K pages, but can perform much larger I/Os, for example during
readahead and after merging writes. After a very short while memory is
completely fragmented.

Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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