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From:   Huang Jianan <huangjianan@oppo.com>
To:     linux-erofs@lists.ozlabs.org
Cc:     huangjianan@oppo.com, guoweichao@oppo.com, guanyuwei@oppo.com,
        yh@oppo.com, zhangshiming@oppo.com, linux-kernel@vger.kernel.org
Subject: [PATCH v2 2/2] erofs: add sysfs node to control sync decompression strategy
Date:   Tue,  9 Nov 2021 15:45:36 +0800
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Although readpage is a synchronous path, there will be no additional
kworker scheduling overhead in non-atomic contexts. So add a sysfs
node to allow disable sync decompression.

Signed-off-by: Huang Jianan <huangjianan@oppo.com>
---
changes since v1:
- leave auto default
- add a disable strategy for sync_decompress

 Documentation/ABI/testing/sysfs-fs-erofs |  9 +++++++++
 fs/erofs/internal.h                      |  4 ++--
 fs/erofs/super.c                         |  2 +-
 fs/erofs/sysfs.c                         | 10 ++++++++++
 fs/erofs/zdata.c                         | 19 ++++++++++++++-----
 5 files changed, 36 insertions(+), 8 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-fs-erofs b/Documentation/ABI/testing/sysfs-fs-erofs
index 86d0d0234473..c84f12004f02 100644
--- a/Documentation/ABI/testing/sysfs-fs-erofs
+++ b/Documentation/ABI/testing/sysfs-fs-erofs
@@ -5,3 +5,12 @@ Description:	Shows all enabled kernel features.
 		Supported features:
 		lz4_0padding, compr_cfgs, big_pcluster, device_table,
 		sb_chksum.
+
+What:		/sys/fs/erofs/<disk>/sync_decompress
+Date:		November 2021
+Contact:	"Huang Jianan" <huangjianan@oppo.com>
+Description:	Control strategy of sync decompression
+		- 0 (defalut, auto): enable for readpage, and enable for
+				     readahead on atomic contexts only,
+		- 1 (force on): enable for readpage and readahead.
+		- 2 (disable): disable for all situations.
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index d0cd712dc222..06a8bbdb378f 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -60,8 +60,8 @@ 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) */
-	bool readahead_sync_decompress;
+	/* strategy of sync decompression (0 - auto, 1 - force on, 2 - disable) */
+	unsigned int sync_decompress;
 
 	/* threshold for decompression synchronously */
 	unsigned int max_sync_decompress_pages;
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index abc1da5d1719..ea223d6c7985 100644
--- a/fs/erofs/super.c
+++ b/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.sync_decompress = 0;
 #endif
 #ifdef CONFIG_EROFS_FS_XATTR
 	set_opt(&ctx->opt, XATTR_USER);
diff --git a/fs/erofs/sysfs.c b/fs/erofs/sysfs.c
index dd328d20c451..a8889b2b65f3 100644
--- a/fs/erofs/sysfs.c
+++ b/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_ATTR_RW_UI(sync_decompress, erofs_mount_opts);
+
 static struct attribute *erofs_attrs[] = {
+	ATTR_LIST(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;
 }
 
@@ -126,6 +132,10 @@ static ssize_t erofs_attr_store(struct kobject *kobj, struct attribute *attr,
 		ret = kstrtoul(skip_spaces(buf), 0, &t);
 		if (ret)
 			return ret;
+		
+		if (!strcmp(a->attr.name, "sync_decompress") && (t > 2))
+			return -EINVAL;
+
 		*((unsigned int *) ptr) = t;
 		return len;
 	case attr_pointer_bool:
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index bcb1b91b234f..70ec51fa7131 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -794,7 +794,8 @@ 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;
+		if (sbi->opt.sync_decompress == 0)
+			sbi->opt.sync_decompress = 1;
 		return;
 	}
 	z_erofs_decompressqueue_work(&io->u.work);
@@ -1454,9 +1455,11 @@ 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;
+	bool force_fg = true;
 
 	trace_erofs_readpage(page, false);
 	f.headoffset = (erofs_off_t)page->index << PAGE_SHIFT;
@@ -1468,8 +1471,11 @@ static int z_erofs_readpage(struct file *file, struct page *page)
 
 	(void)z_erofs_collector_end(&f.clt);
 
+	if (sbi->opt.sync_decompress == 2)
+		force_fg = false;
+
 	/* 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, force_fg);
 
 	if (err)
 		erofs_err(inode->i_sb, "failed to read, err [%d]", err);
@@ -1488,6 +1494,7 @@ static void z_erofs_readahead(struct readahead_control *rac)
 	struct z_erofs_decompress_frontend f = DECOMPRESS_FRONTEND_INIT(inode);
 	struct page *pagepool = NULL, *head = NULL, *page;
 	unsigned int nr_pages;
+	bool force_fg = false;
 
 	f.readahead = true;
 	f.headoffset = readahead_pos(rac);
@@ -1519,9 +1526,11 @@ static void z_erofs_readahead(struct readahead_control *rac)
 	z_erofs_pcluster_readmore(&f, rac, 0, &pagepool, false);
 	(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);
+	if (sbi->opt.sync_decompress == 1)
+		force_fg = true;
+
+	z_erofs_runqueue(inode->i_sb, &f, &pagepool, force_fg
+			 && nr_pages <= sbi->opt.max_sync_decompress_pages);
 	if (f.map.mpage)
 		put_page(f.map.mpage);
 	erofs_release_pages(&pagepool);
-- 
2.25.1