Re: [PATCH] knfsd: Stop NFSD writes from being broken into lots of little writes to filesystem.

NeilBrown wrote:

Another nfsd patch for 2.6.21...

### Comments for Changeset

When NFSD receives a write request, the data is typically in a number
of 1448 byte segments and writev is used to collect them together.

Unfortunately, generic_file_buffered_write passes these to the filesystem
one at a time, so an e.g. 32K over-write becomes a series of partial-page
writes to each page, causing the filesystem to have to pre-read those
pages - wasted effort.

generic_file_buffered_write handles one segment of the vector at a
time as it has to pre-fault in each segment to avoid deadlocks.  When
writing from kernel-space (and nfsd does) this is not an issue, so
generic_file_buffered_write does not need to break and iovec from nfsd
into little pieces.

This patch avoids the splitting when  get_fs is KERNEL_DS as it is
from NFSd.

This issue was introduced by commit 6527c2bdf1f833cc18e8f42bd97973d583e4aa83

Cc: Nick Piggin <[email protected]>

FWIW, you can put Acked-by: me there if you'd like.

Thanks,
Nick

--
SUSE Labs, Novell Inc.

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