fs: remove mpage_alloc

open code mpage_alloc in it's two callers and simplify the results
because of the context:

 - __mpage_writepage always passes GFP_NOFS and can thus always sleep and
    will never get a NULL return from bio_alloc at all.
 - do_mpage_readpage can only get a non-sleeping context for readahead
   which never sets PF_MEMALLOC and thus doesn't need the retry loop
   either.

Both cases will never have __GFP_HIGH set.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220124091107.642561-2-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/mpage.c

@@ -66,29 +66,6 @@ static struct bio *mpage_bio_submit(int op, int op_flags, struct bio *bio)
 	return NULL;
 }
 
-static struct bio *
-mpage_alloc(struct block_device *bdev,
-		sector_t first_sector, int nr_vecs,
-		gfp_t gfp_flags)
-{
-	struct bio *bio;
-
-	/* Restrict the given (page cache) mask for slab allocations */
-	gfp_flags &= GFP_KERNEL;
-	bio = bio_alloc(gfp_flags, nr_vecs);
-
-	if (bio == NULL && (current->flags & PF_MEMALLOC)) {
-		while (!bio && (nr_vecs /= 2))
-			bio = bio_alloc(gfp_flags, nr_vecs);
-	}
-
-	if (bio) {
-		bio_set_dev(bio, bdev);
-		bio->bi_iter.bi_sector = first_sector;
-	}
-	return bio;
-}
-
 /*
  * support function for mpage_readahead.  The fs supplied get_block might
  * return an up to date buffer.  This is used to map that buffer into
@@ -296,10 +273,11 @@ static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
 								page))
 				goto out;
 		}
-		args->bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
-					bio_max_segs(args->nr_pages), gfp);
+		args->bio = bio_alloc(gfp, bio_max_segs(args->nr_pages));
 		if (args->bio == NULL)
 			goto confused;
+		bio_set_dev(args->bio, bdev);
+		args->bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
 	}
 
 	length = first_hole << blkbits;
@@ -608,10 +586,9 @@ static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
 								page, wbc))
 				goto out;
 		}
-		bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
-				BIO_MAX_VECS, GFP_NOFS|__GFP_HIGH);
-		if (bio == NULL)
-			goto confused;
+		bio = bio_alloc(GFP_NOFS, BIO_MAX_VECS);
+		bio_set_dev(bio, bdev);
+		bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
 
 		wbc_init_bio(wbc, bio);
 		bio->bi_write_hint = inode->i_write_hint;