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. So we can add a
sysfs node to allow disable sync decompression.

Signed-off-by: Huang Jianan <huangjianan@oppo.com>

fs/erofs/internal.h

@@ -60,7 +60,7 @@ struct erofs_mount_opts {
 #ifdef CONFIG_EROFS_FS_ZIP
 	/* current strategy of how to use managed cache */
 	unsigned char cache_strategy;
-	/* strategy of sync decompression (false - auto, true - force on) */
+	/* strategy of sync decompression (false - disable, true - force on) */
 	bool readahead_sync_decompress;
 
 	/* threshold for decompression synchronously */

fs/erofs/super.c

@@ -423,7 +423,7 @@ static void erofs_default_options(struct erofs_fs_context *ctx)
 #ifdef CONFIG_EROFS_FS_ZIP
 	ctx->opt.cache_strategy = EROFS_ZIP_CACHE_READAROUND;
 	ctx->opt.max_sync_decompress_pages = 3;
-	ctx->opt.readahead_sync_decompress = false;
+	ctx->opt.readahead_sync_decompress = true;
 #endif
 #ifdef CONFIG_EROFS_FS_XATTR
 	set_opt(&ctx->opt, XATTR_USER);

fs/erofs/sysfs.c

@@ -16,6 +16,7 @@ enum {
 
 enum {
 	struct_erofs_sb_info,
+	struct_erofs_mount_opts,
 };
 
 struct erofs_attr {
@@ -55,7 +56,10 @@ static struct erofs_attr erofs_attr_##_name = {			\
 
 #define ATTR_LIST(name) (&erofs_attr_##name.attr)
 
+EROFS_RW_ATTR_BOOL(readahead_sync_decompress, erofs_mount_opts);
+
 static struct attribute *erofs_attrs[] = {
+	ATTR_LIST(readahead_sync_decompress),
 	NULL,
 };
 ATTRIBUTE_GROUPS(erofs);
@@ -82,6 +86,8 @@ static unsigned char *__struct_ptr(struct erofs_sb_info *sbi,
 {
 	if (struct_type == struct_erofs_sb_info)
 		return (unsigned char *)sbi + offset;
+	if (struct_type == struct_erofs_mount_opts)
+		return (unsigned char *)&sbi->opt + offset;
 	return NULL;
 }
 

fs/erofs/zdata.c

@@ -776,8 +776,6 @@ 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)
 {
-	struct erofs_sb_info *const sbi = EROFS_SB(io->sb);
-
 	/* wake up the caller thread for sync decompression */
 	if (sync) {
 		unsigned long flags;
@@ -791,10 +789,9 @@ static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
 
 	if (atomic_add_return(bios, &io->pending_bios))
 		return;
-	/* Use workqueue and sync decompression for atomic contexts only */
+	/* Use workqueue decompression for atomic contexts only */
 	if (in_atomic() || irqs_disabled()) {
 		queue_work(z_erofs_workqueue, &io->u.work);
-		sbi->opt.readahead_sync_decompress = true;
 		return;
 	}
 	z_erofs_decompressqueue_work(&io->u.work);
@@ -1454,6 +1451,7 @@ static void z_erofs_pcluster_readmore(struct z_erofs_decompress_frontend *f,
 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;
@@ -1469,7 +1467,8 @@ 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,
+			 sbi->opt.readahead_sync_decompress);
 
 	if (err)
 		erofs_err(inode->i_sb, "failed to read, err [%d]", err);