erofs: clean up cached I/O strategies

After commit 4c7e42552b ("erofs: remove useless cache strategy of
DELAYEDALLOC"), only one cached I/O allocation strategy is supported:

  When cached I/O is preferred, page allocation is applied without
  direct reclaim.  If allocation fails, fall back to inplace I/O.

Let's get rid of z_erofs_cache_alloctype.  No logical changes.

Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Yue Hu <huyue2@coolpad.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20221206060352.152830-1-xiang@kernel.org

fs/erofs/zdata.c

@@ -175,16 +175,6 @@ static void z_erofs_free_pcluster(struct z_erofs_pcluster *pcl)
 	DBG_BUGON(1);
 }
 
-/* how to allocate cached pages for a pcluster */
-enum z_erofs_cache_alloctype {
-	DONTALLOC,	/* don't allocate any cached pages */
-	/*
-	 * try to use cached I/O if page allocation succeeds or fallback
-	 * to in-place I/O instead to avoid any direct reclaim.
-	 */
-	TRYALLOC,
-};
-
 /*
  * tagged pointer with 1-bit tag for all compressed pages
  * tag 0 - the page is just found with an extra page reference
@@ -292,12 +282,29 @@ struct z_erofs_decompress_frontend {
 	.inode = __i, .owned_head = Z_EROFS_PCLUSTER_TAIL, \
 	.mode = Z_EROFS_PCLUSTER_FOLLOWED, .backmost = true }
 
+static bool z_erofs_should_alloc_cache(struct z_erofs_decompress_frontend *fe)
+{
+	unsigned int cachestrategy = EROFS_I_SB(fe->inode)->opt.cache_strategy;
+
+	if (cachestrategy <= EROFS_ZIP_CACHE_DISABLED)
+		return false;
+
+	if (fe->backmost)
+		return true;
+
+	if (cachestrategy >= EROFS_ZIP_CACHE_READAROUND &&
+	    fe->map.m_la < fe->headoffset)
+		return true;
+
+	return false;
+}
+
 static void z_erofs_bind_cache(struct z_erofs_decompress_frontend *fe,
-			       enum z_erofs_cache_alloctype type,
 			       struct page **pagepool)
 {
 	struct address_space *mc = MNGD_MAPPING(EROFS_I_SB(fe->inode));
 	struct z_erofs_pcluster *pcl = fe->pcl;
+	bool shouldalloc = z_erofs_should_alloc_cache(fe);
 	bool standalone = true;
 	/*
 	 * optimistic allocation without direct reclaim since inplace I/O
@@ -326,18 +333,19 @@ static void z_erofs_bind_cache(struct z_erofs_decompress_frontend *fe,
 		} else {
 			/* I/O is needed, no possible to decompress directly */
 			standalone = false;
-			switch (type) {
+			if (!shouldalloc)
-			case TRYALLOC:
-				newpage = erofs_allocpage(pagepool, gfp);
-				if (!newpage)
-					continue;
-				set_page_private(newpage,
-						 Z_EROFS_PREALLOCATED_PAGE);
-				t = tag_compressed_page_justfound(newpage);
-				break;
-			default:        /* DONTALLOC */
 				continue;
-			}
+
+			/*
+			 * try to use cached I/O if page allocation
+			 * succeeds or fallback to in-place I/O instead
+			 * to avoid any direct reclaim.
+			 */
+			newpage = erofs_allocpage(pagepool, gfp);
+			if (!newpage)
+				continue;
+			set_page_private(newpage, Z_EROFS_PREALLOCATED_PAGE);
+			t = tag_compressed_page_justfound(newpage);
 		}
 
 		if (!cmpxchg_relaxed(&pcl->compressed_bvecs[i].page, NULL,
@@ -637,20 +645,6 @@ static bool z_erofs_collector_end(struct z_erofs_decompress_frontend *fe)
 	return true;
 }
 
-static bool should_alloc_managed_pages(struct z_erofs_decompress_frontend *fe,
-				       unsigned int cachestrategy,
-				       erofs_off_t la)
-{
-	if (cachestrategy <= EROFS_ZIP_CACHE_DISABLED)
-		return false;
-
-	if (fe->backmost)
-		return true;
-
-	return cachestrategy >= EROFS_ZIP_CACHE_READAROUND &&
-		la < fe->headoffset;
-}
-
 static int z_erofs_read_fragment(struct inode *inode, erofs_off_t pos,
 				 struct page *page, unsigned int pageofs,
 				 unsigned int len)
@@ -687,12 +681,9 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
 				struct page *page, struct page **pagepool)
 {
 	struct inode *const inode = fe->inode;
-	struct erofs_sb_info *const sbi = EROFS_I_SB(inode);
 	struct erofs_map_blocks *const map = &fe->map;
 	const loff_t offset = page_offset(page);
 	bool tight = true, exclusive;
-
-	enum z_erofs_cache_alloctype cache_strategy;
 	unsigned int cur, end, spiltted;
 	int err = 0;
 
@@ -746,13 +737,7 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
 		fe->mode = Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE;
 	} else {
 		/* bind cache first when cached decompression is preferred */
-		if (should_alloc_managed_pages(fe, sbi->opt.cache_strategy,
+		z_erofs_bind_cache(fe, pagepool);
-					       map->m_la))
-			cache_strategy = TRYALLOC;
-		else
-			cache_strategy = DONTALLOC;
-
-		z_erofs_bind_cache(fe, cache_strategy, pagepool);
 	}
 hitted:
 	/*