NFS: Fix /proc/PID/io read_bytes for buffered reads

Prior to commit 8786fde8421c ("Convert NFS from readpages to
readahead"), nfs_readpages() used the old mm interface read_cache_pages()
which called task_io_account_read() for each NFS page read. After
this commit, nfs_readpages() is converted to nfs_readahead(), which
now uses the new mm interface readahead_page(). The new interface
requires callers to call task_io_account_read() themselves.
In addition, to nfs_readahead() task_io_account_read() should also
be called from nfs_read_folio().

Fixes: 8786fde8421c ("Convert NFS from readpages to readahead")
Link: https://lore.kernel.org/linux-nfs/CAPt2mGNEYUk5u8V4abe=5MM5msZqmvzCVrtCP4Qw1n=[e-mail]/
Signed-off-by: Dave Wysochanski <[e-mail]>
Signed-off-by: Anna Schumaker <[e-mail]>

fs/nfs/read.c

···
 #include <linux/stat.h>
 #include <linux/mm.h>
 #include <linux/slab.h>
+#include <linux/task_io_accounting_ops.h>
 #include <linux/pagemap.h>
 #include <linux/sunrpc/clnt.h>
 #include <linux/nfs_fs.h>
···
 
 	trace_nfs_aop_readpage(inode, folio);
 	nfs_inc_stats(inode, NFSIOS_VFSREADPAGE);
+	task_io_account_read(folio_size(folio));
 
 	/*
 	 * Try to flush any pending writes to the file..
···
 
 	trace_nfs_aop_readahead(inode, readahead_pos(ractl), nr_pages);
 	nfs_inc_stats(inode, NFSIOS_VFSREADPAGES);
+	task_io_account_read(readahead_length(ractl));
 
 	ret = -ESTALE;
 	if (NFS_STALE(inode))