erofs: rename per-CPU buffers to global buffer pool and make it configurable

It will cost more time if compressed buffers are allocated on demand for
low-latency algorithms (like lz4) so EROFS uses per-CPU buffers to keep
compressed data if in-place decompression is unfulfilled.  While it is kind
of wasteful of memory for a device with hundreds of CPUs, and only a small
number of CPUs concurrently decompress most of the time.

This patch renames it as 'global buffer pool' and makes it configurable.
This allows two or more CPUs to share a common buffer to reduce memory
occupation.

Suggested-by: Gao Xiang <xiang@kernel.org>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Chunhai Guo <guochunhai@vivo.com>
Link: https://lore.kernel.org/r/20240402100036.2673604-1-guochunhai@vivo.com
Signed-off-by: Sandeep Dhavale <dhavale@google.com>
Link: https://lore.kernel.org/r/20240408215231.3376659-1-dhavale@google.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Author: Chunhai Guo

fs/erofs/Makefile

@@ -3,7 +3,7 @@
 obj-$(CONFIG_EROFS_FS) += erofs.o
 erofs-objs := super.o inode.o data.o namei.o dir.o sysfs.o
 erofs-$(CONFIG_EROFS_FS_XATTR) += xattr.o
-erofs-$(CONFIG_EROFS_FS_ZIP) += decompressor.o zmap.o zdata.o pcpubuf.o zutil.o
+erofs-$(CONFIG_EROFS_FS_ZIP) += decompressor.o zmap.o zdata.o zutil.o
 erofs-$(CONFIG_EROFS_FS_ZIP_LZMA) += decompressor_lzma.o
 erofs-$(CONFIG_EROFS_FS_ZIP_DEFLATE) += decompressor_deflate.o
 erofs-$(CONFIG_EROFS_FS_ONDEMAND) += fscache.o

fs/erofs/decompressor.c

@@ -54,7 +54,7 @@ static int z_erofs_load_lz4_config(struct super_block *sb,
 	sbi->lz4.max_distance_pages = distance ?
 					DIV_ROUND_UP(distance, PAGE_SIZE) + 1 :
 					LZ4_MAX_DISTANCE_PAGES;
-	return erofs_pcpubuf_growsize(sbi->lz4.max_pclusterblks);
+	return z_erofs_gbuf_growsize(sbi->lz4.max_pclusterblks);
 }
 
 /*
@@ -159,7 +159,7 @@ static void *z_erofs_lz4_handle_overlap(struct z_erofs_lz4_decompress_ctx *ctx,
 docopy:
 	/* Or copy compressed data which can be overlapped to per-CPU buffer */
 	in = rq->in;
-	src = erofs_get_pcpubuf(ctx->inpages);
+	src = z_erofs_get_gbuf(ctx->inpages);
 	if (!src) {
 		DBG_BUGON(1);
 		kunmap_local(inpage);
@@ -260,7 +260,7 @@ static int z_erofs_lz4_decompress_mem(struct z_erofs_lz4_decompress_ctx *ctx,
 	} else if (maptype == 1) {
 		vm_unmap_ram(src, ctx->inpages);
 	} else if (maptype == 2) {
-		erofs_put_pcpubuf(src);
+		z_erofs_put_gbuf(src);
 	} else if (maptype != 3) {
 		DBG_BUGON(1);
 		return -EFAULT;

fs/erofs/internal.h

@@ -463,11 +463,11 @@ int erofs_try_to_free_all_cached_folios(struct erofs_sb_info *sbi,
 					struct erofs_workgroup *egrp);
 int z_erofs_map_blocks_iter(struct inode *inode, struct erofs_map_blocks *map,
 			    int flags);
-void *erofs_get_pcpubuf(unsigned int requiredpages);
-void erofs_put_pcpubuf(void *ptr);
-int erofs_pcpubuf_growsize(unsigned int nrpages);
-void __init erofs_pcpubuf_init(void);
-void erofs_pcpubuf_exit(void);
+void *z_erofs_get_gbuf(unsigned int requiredpages);
+void z_erofs_put_gbuf(void *ptr);
+int z_erofs_gbuf_growsize(unsigned int nrpages);
+int __init z_erofs_gbuf_init(void);
+void z_erofs_gbuf_exit(void);
 int erofs_init_managed_cache(struct super_block *sb);
 int z_erofs_parse_cfgs(struct super_block *sb, struct erofs_super_block *dsb);
 #else
@@ -477,8 +477,8 @@ static inline int erofs_init_shrinker(void) { return 0; }
 static inline void erofs_exit_shrinker(void) {}
 static inline int z_erofs_init_zip_subsystem(void) { return 0; }
 static inline void z_erofs_exit_zip_subsystem(void) {}
-static inline void erofs_pcpubuf_init(void) {}
-static inline void erofs_pcpubuf_exit(void) {}
+static inline int z_erofs_gbuf_init(void) { return 0; }
+static inline void z_erofs_gbuf_exit(void) {}
 static inline int erofs_init_managed_cache(struct super_block *sb) { return 0; }
 #endif	/* !CONFIG_EROFS_FS_ZIP */
 

fs/erofs/pcpubuf.c

@@ -859,7 +859,10 @@ static int __init erofs_module_init(void)
 	if (err)
 		goto deflate_err;
 
-	erofs_pcpubuf_init();
+	err = z_erofs_gbuf_init();
+	if (err)
+		goto gbuf_err;
+
 	err = z_erofs_init_zip_subsystem();
 	if (err)
 		goto zip_err;
@@ -879,6 +882,8 @@ static int __init erofs_module_init(void)
 sysfs_err:
 	z_erofs_exit_zip_subsystem();
 zip_err:
+	z_erofs_gbuf_exit();
+gbuf_err:
 	z_erofs_deflate_exit();
 deflate_err:
 	z_erofs_lzma_exit();
@@ -902,7 +907,7 @@ static void __exit erofs_module_exit(void)
 	z_erofs_lzma_exit();
 	erofs_exit_shrinker();
 	kmem_cache_destroy(erofs_inode_cachep);
-	erofs_pcpubuf_exit();
+	z_erofs_gbuf_exit();
 }
 
 static int erofs_statfs(struct dentry *dentry, struct kstatfs *buf)