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From:   David Howells <dhowells@redhat.com>
In-Reply-To: <Y+nzO2H8AizX4lAQ@infradead.org>
References: <Y+nzO2H8AizX4lAQ@infradead.org> <Y+UJAdnllBw+uxK+@casper.infradead.org> <20230209102954.528942-1-dhowells@redhat.com> <20230209102954.528942-2-dhowells@redhat.com> <909202.1675959337@warthog.procyon.org.uk>
To:     Christoph Hellwig <hch@infradead.org>
Cc:     dhowells@redhat.com, Matthew Wilcox <willy@infradead.org>,
        Jens Axboe <axboe@kernel.dk>,
        Al Viro <viro@zeniv.linux.org.uk>, Jan Kara <jack@suse.cz>,
        Jeff Layton <jlayton@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Logan Gunthorpe <logang@deltatee.com>,
        Hillf Danton <hdanton@sina.com>, linux-fsdevel@vger.kernel.org,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org,
        syzbot+a440341a59e3b7142895@syzkaller.appspotmail.com,
        Christoph Hellwig <hch@lst.de>,
        John Hubbard <jhubbard@nvidia.com>
Subject: [PATCH] splice: Clean up direct_splice_read() a bit
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Date:   Wed, 15 Feb 2023 13:42:20 +0000
Message-ID: <3113838.1676468540@warthog.procyon.org.uk>
Precedence: bulk

How about the attached?  I won't fold it down for the moment, but it could=
 be
pushed along later.

David
---
splice: Clean up direct_splice_read() a bit

Do a couple of cleanups to direct_splice_read():

 (1) Cast to struct page **, not void *.

 (2) Simplify the calculation of the number of pages to keep/reclaim in
     direct_splice_read().

Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Christoph Hellwig <hch@lst.de>
cc: Jens Axboe <axboe@kernel.dk>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: David Hildenbrand <david@redhat.com>
cc: John Hubbard <jhubbard@nvidia.com>
cc: linux-mm@kvack.org
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org

diff --git a/fs/splice.c b/fs/splice.c
index 9e798c901087..572d3e2a669a 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -295,7 +295,7 @@ ssize_t direct_splice_read(struct file *in, loff_t *pp=
os,
 	struct kiocb kiocb;
 	struct page **pages;
 	ssize_t ret;
-	size_t used, npages, chunk, remain, reclaim;
+	size_t used, npages, chunk, remain, keep =3D 0;
 	int i;
 =

 	/* Work out how much data we can actually add into the pipe */
@@ -332,11 +332,8 @@ ssize_t direct_splice_read(struct file *in, loff_t *p=
pos,
 	kiocb.ki_pos =3D *ppos;
 	ret =3D call_read_iter(in, &kiocb, &to);
 =

-	reclaim =3D npages * PAGE_SIZE;
-	remain =3D 0;
 	if (ret > 0) {
-		reclaim -=3D ret;
-		remain =3D ret;
+		keep =3D DIV_ROUND_UP(ret, PAGE_SIZE);
 		*ppos =3D kiocb.ki_pos;
 		file_accessed(in);
 	} else if (ret < 0) {
@@ -349,14 +346,12 @@ ssize_t direct_splice_read(struct file *in, loff_t *=
ppos,
 	}
 =

 	/* Free any pages that didn't get touched at all. */
-	reclaim /=3D PAGE_SIZE;
-	if (reclaim) {
-		npages -=3D reclaim;
-		release_pages(pages + npages, reclaim);
-	}
+	if (keep < npages)
+		release_pages(pages + keep, npages - keep);
 =

 	/* Push the remaining pages into the pipe. */
-	for (i =3D 0; i < npages; i++) {
+	remain =3D ret;
+	for (i =3D 0; i < keep; i++) {
 		struct pipe_buffer *buf =3D pipe_head_buf(pipe);
 =

 		chunk =3D min_t(size_t, remain, PAGE_SIZE);