[PATCH 0/2] generic_file_buffered_read improvements

[Kent Overstreet]

Small patch series to
 - firstly, refactor generic_file_buffered_read enough that it can be modified
   in more interesting ways without going insane, and then

 - secondly, change it to use find_get_pages_contig() to batch up the page
   operations, and then copy data to userspace in a separate loop that touches
   no other shared cachelines.

I've been seeing profiles where the radix tree lookups in the buffered read path
are a shockingly large portion of the profile (around 25%, if memory serves) -
that's what this patch series is addressing. I've benchmarked small block reads
as well, performance there is unaffected or slightly improved (it's within the
margin of error).

And as a bonus, the code that was all in generic_file_buffered_read() is now
_drastically_ easier to follow and modify. I haven't done as much refactoring as
I could have, I kept as much of the structure of the old code as I could just to
make things easier on myself, but I'm still pretty happy with the result.

Kent Overstreet (2):
  fs: Break generic_file_buffered_read up into multiple functions
  fs: generic_file_buffered_read() now uses find_get_pages_contig

 mm/filemap.c | 486 +++++++++++++++++++++++++++++----------------------
 1 file changed, 273 insertions(+), 213 deletions(-)

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2.18.0