erofs: use sync decompression for atomic contexts only

Sync decompression was introduced to get rid of additional kworker
scheduling overhead. But there is no such overhead in non-atomic
contexts. Therefore, it should be better to turn off sync decompression
to avoid the current thread waiting in z_erofs_runqueue.

Link: https://lore.kernel.org/r/20210317035448.13921-3-huangjianan@oppo.comReviewed-by: Gao Xiang <hsiangkao@redhat.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Huang Jianan <huangjianan@oppo.com>
Signed-off-by: Guo Weichao <guoweichao@oppo.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

fs/erofs/internal.h

@@ -50,6 +50,8 @@ struct erofs_fs_context {
 #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) */
+	bool readahead_sync_decompress;
 
 	/* threshold for decompression synchronously */
 	unsigned int max_sync_decompress_pages;

fs/erofs/super.c

@@ -200,6 +200,7 @@ static void erofs_default_options(struct erofs_fs_context *ctx)
 #ifdef CONFIG_EROFS_FS_ZIP
 	ctx->cache_strategy = EROFS_ZIP_CACHE_READAROUND;
 	ctx->max_sync_decompress_pages = 3;
+	ctx->readahead_sync_decompress = false;
 #endif
 #ifdef CONFIG_EROFS_FS_XATTR
 	set_opt(ctx, XATTR_USER);

fs/erofs/zdata.c

@@ -710,6 +710,8 @@ 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;
@@ -723,9 +725,10 @@ static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
 
 	if (atomic_add_return(bios, &io->pending_bios))
 		return;
-	/* Use workqueue decompression for atomic contexts only */
+	/* Use workqueue and sync decompression for atomic contexts only */
 	if (in_atomic() || irqs_disabled()) {
 		queue_work(z_erofs_workqueue, &io->u.work);
+		sbi->ctx.readahead_sync_decompress = true;
 		return;
 	}
 	z_erofs_decompressqueue_work(&io->u.work);
@@ -1340,7 +1343,8 @@ static void z_erofs_readahead(struct readahead_control *rac)
 	struct erofs_sb_info *const sbi = EROFS_I_SB(inode);
 
 	unsigned int nr_pages = readahead_count(rac);
-	bool sync = (nr_pages <= sbi->ctx.max_sync_decompress_pages);
+	bool sync = (sbi->ctx.readahead_sync_decompress &&
+			nr_pages <= sbi->ctx.max_sync_decompress_pages);
 	struct z_erofs_decompress_frontend f = DECOMPRESS_FRONTEND_INIT(inode);
 	struct page *page, *head = NULL;
 	LIST_HEAD(pagepool);