Fixup patch for [PATCH 0/2] generic_file_buffered_read() refactoring & optimization

Kent Overstreet
2020-06-30T00:12:40Z

Andrew - fixup patch because I got a bug report where we were trying to do an
order 7 allocation here:

-- >8 --
Subject: [PATCH] fixup! fs: generic_file_buffered_read() now uses
find_get_pages_contig

We shouldn't try to pin too many pages at once, reads can be almost
arbitrarily big.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
---
mm/filemap.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index d8bd5e9647..b3a2aad1b7 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2220,8 +2220,9 @@ static ssize_t generic_file_buffered_read(struct kiocb *iocb,
struct inode *inode = mapping->host;
size_t orig_count = iov_iter_count(iter);
struct page *pages_onstack[8], **pages = NULL;
- unsigned int nr_pages = ((iocb->ki_pos + iter->count + PAGE_SIZE - 1) >> PAGE_SHIFT) -
- (iocb->ki_pos >> PAGE_SHIFT);
+ unsigned int nr_pages = min_t(unsigned int, 512,
+ ((iocb->ki_pos + iter->count + PAGE_SIZE - 1) >> PAGE_SHIFT) -
+ (iocb->ki_pos >> PAGE_SHIFT));
int i, pg_nr, error = 0;
bool writably_mapped;
loff_t isize, end_offset;
--
2.27.0