[PATCH v6 17/24] erofs: introduce per-CPU buffers implementation

[Gao Xiang]

This patch introduces per-CPU buffers in order for
the upcoming generic decompression framework to use.

Note that I tried to use in-kernel per-CPU buffer or
per-CPU page approaches to clean up further, however
noticeable performanace regression (about 2% for
sequential read) was observed.

Let's leave it as-is for now.

Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx>
---
 fs/erofs/Kconfig    | 14 ++++++++++++++
 fs/erofs/internal.h | 21 +++++++++++++++++++++
 fs/erofs/utils.c    | 12 ++++++++++++
 3 files changed, 47 insertions(+)

diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
index a475fbebb831..5f8787c0cf89 100644
--- a/fs/erofs/Kconfig
+++ b/fs/erofs/Kconfig
@@ -81,3 +81,17 @@ config EROFS_FS_ZIP
 
 	  If you don't want to enable compression feature, say N.
 
+config EROFS_FS_CLUSTER_PAGE_LIMIT
+	int "EROFS Cluster Pages Hard Limit"
+	depends on EROFS_FS_ZIP
+	range 1 256
+	default "1"
+	help
+	  Indicates maximum # of pages of a compressed
+	  physical cluster.
+
+	  For example, if files in a image were compressed
+	  into 8k-unit, hard limit should not be configured
+	  less than 2. Otherwise, the image will be refused
+	  to mount on this kernel.
+
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 6f0384c3f07a..19694886dda9 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -223,6 +223,12 @@ static inline int erofs_wait_on_workgroup_freezed(struct erofs_workgroup *grp)
 	return v;
 }
 #endif	/* !CONFIG_SMP */
+
+/* hard limit of pages per compressed cluster */
+#define Z_EROFS_CLUSTER_MAX_PAGES       (CONFIG_EROFS_FS_CLUSTER_PAGE_LIMIT)
+#define EROFS_PCPUBUF_NR_PAGES          Z_EROFS_CLUSTER_MAX_PAGES
+#else
+#define EROFS_PCPUBUF_NR_PAGES          0
 #endif	/* !CONFIG_EROFS_FS_ZIP */
 
 /* we strictly follow PAGE_SIZE and no buffer head yet */
@@ -483,6 +489,21 @@ int erofs_namei(struct inode *dir, struct qstr *name,
 extern const struct file_operations erofs_dir_fops;
 
 /* utils.c */
+#if (EROFS_PCPUBUF_NR_PAGES > 0)
+void *erofs_get_pcpubuf(unsigned int pagenr);
+#define erofs_put_pcpubuf(buf) do { \
+	(void)&(buf);	\
+	preempt_enable();	\
+} while (0)
+#else
+static inline void *erofs_get_pcpubuf(unsigned int pagenr)
+{
+	return ERR_PTR(-ENOTSUPP);
+}
+
+#define erofs_put_pcpubuf(buf) do {} while (0)
+#endif
+
 #ifdef CONFIG_EROFS_FS_ZIP
 int erofs_workgroup_put(struct erofs_workgroup *grp);
 struct erofs_workgroup *erofs_find_workgroup(struct super_block *sb,
diff --git a/fs/erofs/utils.c b/fs/erofs/utils.c
index 628178261056..f3eed9af24d6 100644
--- a/fs/erofs/utils.c
+++ b/fs/erofs/utils.c
@@ -9,6 +9,18 @@
 #include "internal.h"
 #include <linux/pagevec.h>
 
+#if (EROFS_PCPUBUF_NR_PAGES > 0)
+static struct {
+	u8 data[PAGE_SIZE * EROFS_PCPUBUF_NR_PAGES];
+} ____cacheline_aligned_in_smp erofs_pcpubuf[NR_CPUS];
+
+void *erofs_get_pcpubuf(unsigned int pagenr)
+{
+	preempt_disable();
+	return &erofs_pcpubuf[smp_processor_id()].data[pagenr * PAGE_SIZE];
+}
+#endif
+
 #ifdef CONFIG_EROFS_FS_ZIP
 /* global shrink count (for all mounted EROFS instances) */
 static atomic_long_t erofs_global_shrink_cnt;
-- 
2.17.1