erofs: add sysfs node to control sync decompression strategy

Although readpage is a synchronous path, there will be no additional
kworker scheduling overhead in non-atomic contexts together with
dm-verity.

Let's add a sysfs node to disable sync decompression as an option.

Link: https://lore.kernel.org/r/20211206143552.8384-1-huangjianan@oppo.com
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Huang Jianan <huangjianan@oppo.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

1 files changed, 22 insertions, 4 deletions

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 9a249bfc2770..bc765d8a6dc2 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -762,6 +762,21 @@ err_out:
 	goto out;
 }
 
+static bool z_erofs_get_sync_decompress_policy(struct erofs_sb_info *sbi,
+				       unsigned int readahead_pages)
+{
+	/* auto: enable for readpage, disable for readahead */
+	if ((sbi->opt.sync_decompress == EROFS_SYNC_DECOMPRESS_AUTO) &&
+	    !readahead_pages)
+		return true;
+
+	if ((sbi->opt.sync_decompress == EROFS_SYNC_DECOMPRESS_FORCE_ON) &&
+	    (readahead_pages <= sbi->opt.max_sync_decompress_pages))
+		return true;
+
+	return false;
+}
+
 static void z_erofs_decompressqueue_work(struct work_struct *work);
 static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
 				       bool sync, int bios)
@@ -784,7 +799,9 @@ static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
 	/* Use workqueue and sync decompression for atomic contexts only */
 	if (in_atomic() || irqs_disabled()) {
 		queue_work(z_erofs_workqueue, &io->u.work);
-		sbi->opt.readahead_sync_decompress = true;
+		/* enable sync decompression for readahead */
+		if (sbi->opt.sync_decompress == EROFS_SYNC_DECOMPRESS_AUTO)
+			sbi->opt.sync_decompress = EROFS_SYNC_DECOMPRESS_FORCE_ON;
 		return;
 	}
 	z_erofs_decompressqueue_work(&io->u.work);
@@ -1435,6 +1452,7 @@ skip:
 static int z_erofs_readpage(struct file *file, struct page *page)
 {
 	struct inode *const inode = page->mapping->host;
+	struct erofs_sb_info *const sbi = EROFS_I_SB(inode);
 	struct z_erofs_decompress_frontend f = DECOMPRESS_FRONTEND_INIT(inode);
 	struct page *pagepool = NULL;
 	int err;
@@ -1450,7 +1468,8 @@ static int z_erofs_readpage(struct file *file, struct page *page)
 	(void)z_erofs_collector_end(&f.clt);
 
 	/* if some compressed cluster ready, need submit them anyway */
-	z_erofs_runqueue(inode->i_sb, &f, &pagepool, true);
+	z_erofs_runqueue(inode->i_sb, &f, &pagepool,
+			 z_erofs_get_sync_decompress_policy(sbi, 0));
 
 	if (err)
 		erofs_err(inode->i_sb, "failed to read, err [%d]", err);
@@ -1501,8 +1520,7 @@ static void z_erofs_readahead(struct readahead_control *rac)
 	(void)z_erofs_collector_end(&f.clt);
 
 	z_erofs_runqueue(inode->i_sb, &f, &pagepool,
-			 sbi->opt.readahead_sync_decompress &&
-			 nr_pages <= sbi->opt.max_sync_decompress_pages);
+			 z_erofs_get_sync_decompress_policy(sbi, nr_pages));
 	if (f.map.mpage)
 		put_page(f.map.mpage);
 	erofs_release_pages(&pagepool);