erofs: get rid of `z_pagemap_global'

In order to introduce multi-reference pclusters for compressed data
deduplication, let's get rid of the global page array for now since
it needs to be re-designed then at least.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

fs/erofs/zdata.c

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 6a7a45a..6410ba2 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -292,9 +292,6 @@ struct z_erofs_decompress_frontend {
 	.inode = __i, .owned_head = Z_EROFS_PCLUSTER_TAIL, \
 	.mode = Z_EROFS_PCLUSTER_FOLLOWED, .backmost = true }
 
-static struct page *z_pagemap_global[Z_EROFS_VMAP_GLOBAL_PAGES];
-static DEFINE_MUTEX(z_pagemap_global_lock);
-
 static void z_erofs_bind_cache(struct z_erofs_decompress_frontend *fe,
 			       enum z_erofs_cache_alloctype type,
 			       struct page **pagepool)
@@ -965,26 +962,11 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
 	mutex_lock(&pcl->lock);
 	nr_pages = pcl->nr_pages;
 
-	if (nr_pages <= Z_EROFS_VMAP_ONSTACK_PAGES) {
+	if (nr_pages <= Z_EROFS_VMAP_ONSTACK_PAGES)
 		pages = pages_onstack;
-	} else if (nr_pages <= Z_EROFS_VMAP_GLOBAL_PAGES &&
-		   mutex_trylock(&z_pagemap_global_lock)) {
-		pages = z_pagemap_global;
-	} else {
-		gfp_t gfp_flags = GFP_KERNEL;
-
-		if (nr_pages > Z_EROFS_VMAP_GLOBAL_PAGES)
-			gfp_flags |= __GFP_NOFAIL;
-
+	else
 		pages = kvmalloc_array(nr_pages, sizeof(struct page *),
-				       gfp_flags);
-
-		/* fallback to global pagemap for the lowmem scenario */
-		if (!pages) {
-			mutex_lock(&z_pagemap_global_lock);
-			pages = z_pagemap_global;
-		}
-	}
+				       GFP_KERNEL | __GFP_NOFAIL);
 
 	for (i = 0; i < nr_pages; ++i)
 		pages[i] = NULL;
@@ -1062,9 +1044,7 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
 		z_erofs_onlinepage_endio(page);
 	}
 
-	if (pages == z_pagemap_global)
-		mutex_unlock(&z_pagemap_global_lock);
-	else if (pages != pages_onstack)
+	if (pages != pages_onstack)
 		kvfree(pages);
 
 	pcl->nr_pages = 0;

fs/erofs/zdata.h

diff --git a/fs/erofs/zdata.h b/fs/erofs/zdata.h
index 8ecb69e..b3b3402 100644
--- a/fs/erofs/zdata.h
+++ b/fs/erofs/zdata.h
@@ -174,6 +174,5 @@ static inline void z_erofs_onlinepage_endio(struct page *page)
 
 #define Z_EROFS_VMAP_ONSTACK_PAGES	\
 	min_t(unsigned int, THREAD_SIZE / 8 / sizeof(struct page *), 96U)
-#define Z_EROFS_VMAP_GLOBAL_PAGES	2048
 
 #endif