erofs: allocate extra bvec pages directly instead of retrying

If non-bootstrap bvecs cannot be kept in place (very rarely), an extra
short-lived page is allocated.

Let's just allocate it immediately rather than do unnecessary -EAGAIN
return first and retry as a cleanup.  Also it's unnecessary to use
__GFP_NOFAIL here since we could gracefully fail out this case instead.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Link: https://lore.kernel.org/r/20230526201459.128169-2-hsiangkao@linux.alibaba.com

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 305426a717925cc74db1af332a1864f92ff0610d..9d04fa29b74279ac6fdf5afd7f4c03f9066be43c 100644 (file)
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -242,12 +242,17 @@ static int z_erofs_bvec_enqueue(struct z_erofs_bvec_iter *iter,
                                struct z_erofs_bvec *bvec,
                                struct page **candidate_bvpage)
 {
-       if (iter->cur == iter->nr) {
-               if (!*candidate_bvpage)
-                       return -EAGAIN;
-
+       if (iter->cur >= iter->nr) {
+               struct page *nextpage = *candidate_bvpage;
+
+               if (!nextpage) {
+                       nextpage = alloc_page(GFP_NOFS);
+                       if (!nextpage)
+                               return -ENOMEM;
+                       set_page_private(nextpage, Z_EROFS_SHORTLIVED_PAGE);
+               }
                DBG_BUGON(iter->bvset->nextpage);
-               iter->bvset->nextpage = *candidate_bvpage;
+               iter->bvset->nextpage = nextpage;
                z_erofs_bvset_flip(iter);
 
                iter->bvset->nextpage = NULL;
@@ -906,10 +911,8 @@ static bool z_erofs_collector_end(struct z_erofs_decompress_frontend *fe)
        z_erofs_bvec_iter_end(&fe->biter);
        mutex_unlock(&pcl->lock);
 
-       if (fe->candidate_bvpage) {
-               DBG_BUGON(z_erofs_is_shortlived_page(fe->candidate_bvpage));
+       if (fe->candidate_bvpage)
                fe->candidate_bvpage = NULL;
-       }
 
        /*
         * if all pending pages are added, don't hold its reference
@@ -1054,24 +1057,13 @@ hitted:
        if (cur)
                tight &= (fe->mode >= Z_EROFS_PCLUSTER_FOLLOWED);
 
-retry:
        err = z_erofs_attach_page(fe, &((struct z_erofs_bvec) {
                                        .page = page,
                                        .offset = offset - map->m_la,
                                        .end = end,
                                  }), exclusive);
-       /* should allocate an additional short-lived page for bvset */
-       if (err == -EAGAIN && !fe->candidate_bvpage) {
-               fe->candidate_bvpage = alloc_page(GFP_NOFS | __GFP_NOFAIL);
-               set_page_private(fe->candidate_bvpage,
-                                Z_EROFS_SHORTLIVED_PAGE);
-               goto retry;
-       }
-
-       if (err) {
-               DBG_BUGON(err == -EAGAIN && fe->candidate_bvpage);
+       if (err)
                goto out;
-       }
 
        z_erofs_onlinepage_split(page);
        /* bump up the number of spiltted parts of a page */