[PATCH v4 19/24] erofs: add erofs_allocpage()

[Gao Xiang]

This patch introduces an temporary _on-stack_ page
pool to reuse the freed page directly as much as
it can for better performance and release all pages
at a time, it also slightly reduces the possibility of
the potential memory allocation failure.

Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx>
---
 fs/erofs/internal.h |  2 ++
 fs/erofs/utils.c    | 14 ++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 410e1b7ef82e..d450ab130d5e 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -492,6 +492,8 @@ int erofs_namei(struct inode *dir, struct qstr *name,
 extern const struct file_operations erofs_dir_fops;
 
 /* utils.c */
+struct page *erofs_allocpage(struct list_head *pool, gfp_t gfp, bool nofail);
+
 #if (EROFS_PCPUBUF_NR_PAGES > 0)
 void *erofs_get_pcpubuf(unsigned int pagenr);
 #define erofs_put_pcpubuf(buf) do { \
diff --git a/fs/erofs/utils.c b/fs/erofs/utils.c
index ffaa226746b8..34d0aad1af83 100644
--- a/fs/erofs/utils.c
+++ b/fs/erofs/utils.c
@@ -9,6 +9,20 @@
 #include "internal.h"
 #include <linux/pagevec.h>
 
+struct page *erofs_allocpage(struct list_head *pool, gfp_t gfp, bool nofail)
+{
+	struct page *page;
+
+	if (!list_empty(pool)) {
+		page = lru_to_page(pool);
+		DBG_BUGON(page_ref_count(page) != 1);
+		list_del(&page->lru);
+	} else {
+		page = alloc_pages(gfp | (nofail ? __GFP_NOFAIL : 0), 0);
+	}
+	return page;
+}
+
 #if (EROFS_PCPUBUF_NR_PAGES > 0)
 static struct {
 	u8 data[PAGE_SIZE * EROFS_PCPUBUF_NR_PAGES];
-- 
2.17.1