linux-kernel - Fixup patch for [PATCH 0/2] generic_file_buffered

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Message-ID: <20200630001233.GA39358@moria.home.lan>
Date:   Mon, 29 Jun 2020 20:12:33 -0400
From:   Kent Overstreet <kent.overstreet@...il.com>
To:     linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        viro@...iv.linux.org.uk, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org
Subject: Fixup patch for [PATCH 0/2] generic_file_buffered_read() refactoring
 & optimization

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@...il.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