mm/filemap.c: generic_file_buffered_read() now uses find_get_pages_contig

Convert generic_file_buffered_read() to get pages to read from in batches,
and then copy data to userspace from many pages at once - in particular,
we now don't touch any cachelines that might be contended while we're in
the loop to copy data to userspace.

This is is a performance improvement on workloads that do buffered reads
with large blocksizes, and a very large performance improvement if that
file is also being accessed concurrently by different threads.

On smaller reads (512 bytes), there's a very small performance improvement
(1%, within the margin of error).

akpm: kernel test robot found a 32% speedup on one test:
https://lkml.kernel.org/r/20201030081456.GY31092@shao2-debian

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Kent Overstreet <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: kernel test robot <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions