Increasing the batch size runs into diminishing returns.  It's probably
better to make, eg, three calls to filemap_get_pages() than it is to call
into kmalloc().

Link: https://lkml.kernel.org/r/20210122160140.223228-3-willy@infradead.orgSigned-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NMiaohe Lin <linmiaohe@huawei.com>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>