mm: refactor readahead defines in mm.h

All users of VM_MAX_READAHEAD actually convert it to kbytes and then to
pages. Define the macro explicitly as (SZ_128K / PAGE_SIZE). This
simplifies the expression in every filesystem. Also rename the macro to
VM_READAHEAD_PAGES to properly convey its meaning. Finally remove unused
VM_MIN_READAHEAD

[akpm@linux-foundation.org: fix fs/io_uring.c, per Stephen]
Link: http://lkml.kernel.org/r/20181221144053.24318-1-nborisov@suse.com
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Matthew Wilcox <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Cc: Dominique Martinet <asmadeus@codewreck.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: David Sterba <dsterba@suse.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 5d99376d2369..c88088d92613 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -923,7 +923,7 @@ static void io_async_list_note(int rw, struct io_kiocb *req, size_t len)
 		/* Use 8x RA size as a decent limiter for both reads/writes */
 		max_pages = filp->f_ra.ra_pages;
 		if (!max_pages)
-			max_pages = VM_MAX_READAHEAD >> (PAGE_SHIFT - 10);
+			max_pages = VM_READAHEAD_PAGES;
 		max_pages *= 8;
 
 		/* If max pages are exceeded, reset the state */