squashfs: migrate from ll_rw_block usage to BIO

ll_rw_block() function has been deprecated in favor of BIO which appears
to come with large performance improvements.

This patch decreases boot time by close to 40% when using squashfs for
the root file-system.  This is observed at least in the context of
starting an Android VM on Chrome OS using crosvm.  The patch was tested
on 4.19 as well as master.

This patch is largely based on Adrien Schildknecht's patch that was
originally sent as https://lkml.org/lkml/2017/9/22/814 though with some
significant changes and simplifications while also taking Phillip
Lougher's feedback into account, around preserving support for
FILE_CACHE in particular.

[akpm@linux-foundation.org: fix build error reported by Randy]
  Link: http://lkml.kernel.org/r/319997c2-5fc8-f889-2ea3-d913308a7c1f@infradead.org
Signed-off-by: Philippe Liard <pliard@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Adrien Schildknecht <adrien+dev@schischi.me>
Cc: Phillip Lougher <phillip@squashfs.org.uk>
Cc: Guenter Roeck <groeck@chromium.org>
Cc: Daniel Rosenberg <drosen@google.com>
Link: https://chromium.googlesource.com/chromiumos/platform/crosvm
Link: http://lkml.kernel.org/r/20191106074238.186023-1-pliard@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 33 insertions, 31 deletions

diff --git a/fs/squashfs/zstd_wrapper.c b/fs/squashfs/zstd_wrapper.c
index b448c2a1d0ed..b7cb1faa652d 100644
--- a/fs/squashfs/zstd_wrapper.c
+++ b/fs/squashfs/zstd_wrapper.c
@@ -9,7 +9,7 @@
  */
 
 #include <linux/mutex.h>
-#include <linux/buffer_head.h>
+#include <linux/bio.h>
 #include <linux/slab.h>
 #include <linux/zstd.h>
 #include <linux/vmalloc.h>
@@ -59,33 +59,44 @@ static void zstd_free(void *strm)
 
 
 static int zstd_uncompress(struct squashfs_sb_info *msblk, void *strm,
-	struct buffer_head **bh, int b, int offset, int length,
+	struct bio *bio, int offset, int length,
 	struct squashfs_page_actor *output)
 {
 	struct workspace *wksp = strm;
 	ZSTD_DStream *stream;
 	size_t total_out = 0;
-	size_t zstd_err;
-	int k = 0;
+	int error = 0;
 	ZSTD_inBuffer in_buf = { NULL, 0, 0 };
 	ZSTD_outBuffer out_buf = { NULL, 0, 0 };
+	struct bvec_iter_all iter_all = {};
+	struct bio_vec *bvec = bvec_init_iter_all(&iter_all);
 
 	stream = ZSTD_initDStream(wksp->window_size, wksp->mem, wksp->mem_size);
 
 	if (!stream) {
 		ERROR("Failed to initialize zstd decompressor\n");
-		goto out;
+		return -EIO;
 	}
 
 	out_buf.size = PAGE_SIZE;
 	out_buf.dst = squashfs_first_page(output);
 
-	do {
-		if (in_buf.pos == in_buf.size && k < b) {
-			int avail = min(length, msblk->devblksize - offset);
+	for (;;) {
+		size_t zstd_err;
 
+		if (in_buf.pos == in_buf.size) {
+			const void *data;
+			int avail;
+
+			if (!bio_next_segment(bio, &iter_all)) {
+				error = -EIO;
+				break;
+			}
+
+			avail = min(length, ((int)bvec->bv_len) - offset);
+			data = page_address(bvec->bv_page) + bvec->bv_offset;
 			length -= avail;
-			in_buf.src = bh[k]->b_data + offset;
+			in_buf.src = data + offset;
 			in_buf.size = avail;
 			in_buf.pos = 0;
 			offset = 0;
@@ -97,8 +108,8 @@ static int zstd_uncompress(struct squashfs_sb_info *msblk, void *strm,
 				/* Shouldn't run out of pages
 				 * before stream is done.
 				 */
-				squashfs_finish_page(output);
-				goto out;
+				error = -EIO;
+				break;
 			}
 			out_buf.pos = 0;
 			out_buf.size = PAGE_SIZE;
@@ -107,29 +118,20 @@ static int zstd_uncompress(struct squashfs_sb_info *msblk, void *strm,
 		total_out -= out_buf.pos;
 		zstd_err = ZSTD_decompressStream(stream, &out_buf, &in_buf);
 		total_out += out_buf.pos; /* add the additional data produced */
-
-		if (in_buf.pos == in_buf.size && k < b)
-			put_bh(bh[k++]);
-	} while (zstd_err != 0 && !ZSTD_isError(zstd_err));
-
-	squashfs_finish_page(output);
-
-	if (ZSTD_isError(zstd_err)) {
-		ERROR("zstd decompression error: %d\n",
-				(int)ZSTD_getErrorCode(zstd_err));
-		goto out;
+		if (zstd_err == 0)
+			break;
+
+		if (ZSTD_isError(zstd_err)) {
+			ERROR("zstd decompression error: %d\n",
+					(int)ZSTD_getErrorCode(zstd_err));
+			error = -EIO;
+			break;
+		}
 	}
 
-	if (k < b)
-		goto out;
-
-	return (int)total_out;
-
-out:
-	for (; k < b; k++)
-		put_bh(bh[k]);
+	squashfs_finish_page(output);
 
-	return -EIO;
+	return error ? error : total_out;
 }
 
 const struct squashfs_decompressor squashfs_zstd_comp_ops = {