On Mon, Oct 31, 2011 at 11:16:59AM -0500, Shawn Bohrer wrote:

Previously POSIX_FADV_DONTNEED would start writeback for the entire file
when the bdi was not write congested.  This negatively impacts
performance if the file contians dirty pages outside of the requested
range.  This change uses __filemap_fdatawrite_range() to only initiate
writeback for the requested range.

Signed-off-by: Shawn Bohrer <redacted>

It probably makes sense for some cases to take advantage of the disk
head being nearby and flush more than requested.

But I can certainly see this go wrong by taking away the write-caching
benefits for the rest of the file just because a small part of it was
fadvised.

Acked-by: Johannes Weiner <redacted>

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